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README

1# SPDX-License-Identifier: GPL-2.0+
2#
3# (C) Copyright 2000 - 2013
4# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
5
6Summary:
7========
8
9This directory contains the source code for U-Boot, a boot loader for
10Embedded boards based on PowerPC, ARM, MIPS and several other
11processors, which can be installed in a boot ROM and used to
12initialize and test the hardware or to download and run application
13code.
14
15The development of U-Boot is closely related to Linux: some parts of
16the source code originate in the Linux source tree, we have some
17header files in common, and special provision has been made to
18support booting of Linux images.
19
20Some attention has been paid to make this software easily
21configurable and extendable. For instance, all monitor commands are
22implemented with the same call interface, so that it's very easy to
23add new commands. Also, instead of permanently adding rarely used
24code (for instance hardware test utilities) to the monitor, you can
25load and run it dynamically.
26
27
28Status:
29=======
30
31In general, all boards for which a configuration option exists in the
32Makefile have been tested to some extent and can be considered
33"working". In fact, many of them are used in production systems.
34
35In case of problems see the CHANGELOG file to find out who contributed
36the specific port. In addition, there are various MAINTAINERS files
37scattered throughout the U-Boot source identifying the people or
38companies responsible for various boards and subsystems.
39
40Note: As of August, 2010, there is no longer a CHANGELOG file in the
41actual U-Boot source tree; however, it can be created dynamically
42from the Git log using:
43
44	make CHANGELOG
45
46
47Where to get help:
48==================
49
50In case you have questions about, problems with or contributions for
51U-Boot, you should send a message to the U-Boot mailing list at
52<u-boot@lists.denx.de>. There is also an archive of previous traffic
53on the mailing list - please search the archive before asking FAQ's.
54Please see http://lists.denx.de/pipermail/u-boot and
55http://dir.gmane.org/gmane.comp.boot-loaders.u-boot
56
57
58Where to get source code:
59=========================
60
61The U-Boot source code is maintained in the Git repository at
62git://www.denx.de/git/u-boot.git ; you can browse it online at
63http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary
64
65The "snapshot" links on this page allow you to download tarballs of
66any version you might be interested in. Official releases are also
67available for FTP download from the ftp://ftp.denx.de/pub/u-boot/
68directory.
69
70Pre-built (and tested) images are available from
71ftp://ftp.denx.de/pub/u-boot/images/
72
73
74Where we come from:
75===================
76
77- start from 8xxrom sources
78- create PPCBoot project (http://sourceforge.net/projects/ppcboot)
79- clean up code
80- make it easier to add custom boards
81- make it possible to add other [PowerPC] CPUs
82- extend functions, especially:
83  * Provide extended interface to Linux boot loader
84  * S-Record download
85  * network boot
86  * ATA disk / SCSI ... boot
87- create ARMBoot project (http://sourceforge.net/projects/armboot)
88- add other CPU families (starting with ARM)
89- create U-Boot project (http://sourceforge.net/projects/u-boot)
90- current project page: see http://www.denx.de/wiki/U-Boot
91
92
93Names and Spelling:
94===================
95
96The "official" name of this project is "Das U-Boot". The spelling
97"U-Boot" shall be used in all written text (documentation, comments
98in source files etc.). Example:
99
100	This is the README file for the U-Boot project.
101
102File names etc. shall be based on the string "u-boot". Examples:
103
104	include/asm-ppc/u-boot.h
105
106	#include <asm/u-boot.h>
107
108Variable names, preprocessor constants etc. shall be either based on
109the string "u_boot" or on "U_BOOT". Example:
110
111	U_BOOT_VERSION		u_boot_logo
112	IH_OS_U_BOOT		u_boot_hush_start
113
114
115Versioning:
116===========
117
118Starting with the release in October 2008, the names of the releases
119were changed from numerical release numbers without deeper meaning
120into a time stamp based numbering. Regular releases are identified by
121names consisting of the calendar year and month of the release date.
122Additional fields (if present) indicate release candidates or bug fix
123releases in "stable" maintenance trees.
124
125Examples:
126	U-Boot v2009.11	    - Release November 2009
127	U-Boot v2009.11.1   - Release 1 in version November 2009 stable tree
128	U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release
129
130
131Directory Hierarchy:
132====================
133
134/arch			Architecture specific files
135  /arc			Files generic to ARC architecture
136  /arm			Files generic to ARM architecture
137  /m68k			Files generic to m68k architecture
138  /microblaze		Files generic to microblaze architecture
139  /mips			Files generic to MIPS architecture
140  /nds32		Files generic to NDS32 architecture
141  /nios2		Files generic to Altera NIOS2 architecture
142  /openrisc		Files generic to OpenRISC architecture
143  /powerpc		Files generic to PowerPC architecture
144  /riscv		Files generic to RISC-V architecture
145  /sandbox		Files generic to HW-independent "sandbox"
146  /sh			Files generic to SH architecture
147  /x86			Files generic to x86 architecture
148/api			Machine/arch independent API for external apps
149/board			Board dependent files
150/cmd			U-Boot commands functions
151/common			Misc architecture independent functions
152/configs		Board default configuration files
153/disk			Code for disk drive partition handling
154/doc			Documentation (don't expect too much)
155/drivers		Commonly used device drivers
156/dts			Contains Makefile for building internal U-Boot fdt.
157/examples		Example code for standalone applications, etc.
158/fs			Filesystem code (cramfs, ext2, jffs2, etc.)
159/include		Header Files
160/lib			Library routines generic to all architectures
161/Licenses		Various license files
162/net			Networking code
163/post			Power On Self Test
164/scripts		Various build scripts and Makefiles
165/test			Various unit test files
166/tools			Tools to build S-Record or U-Boot images, etc.
167
168Software Configuration:
169=======================
170
171Configuration is usually done using C preprocessor defines; the
172rationale behind that is to avoid dead code whenever possible.
173
174There are two classes of configuration variables:
175
176* Configuration _OPTIONS_:
177  These are selectable by the user and have names beginning with
178  "CONFIG_".
179
180* Configuration _SETTINGS_:
181  These depend on the hardware etc. and should not be meddled with if
182  you don't know what you're doing; they have names beginning with
183  "CONFIG_SYS_".
184
185Previously, all configuration was done by hand, which involved creating
186symbolic links and editing configuration files manually. More recently,
187U-Boot has added the Kbuild infrastructure used by the Linux kernel,
188allowing you to use the "make menuconfig" command to configure your
189build.
190
191
192Selection of Processor Architecture and Board Type:
193---------------------------------------------------
194
195For all supported boards there are ready-to-use default
196configurations available; just type "make <board_name>_defconfig".
197
198Example: For a TQM823L module type:
199
200	cd u-boot
201	make TQM823L_defconfig
202
203Note: If you're looking for the default configuration file for a board
204you're sure used to be there but is now missing, check the file
205doc/README.scrapyard for a list of no longer supported boards.
206
207Sandbox Environment:
208--------------------
209
210U-Boot can be built natively to run on a Linux host using the 'sandbox'
211board. This allows feature development which is not board- or architecture-
212specific to be undertaken on a native platform. The sandbox is also used to
213run some of U-Boot's tests.
214
215See doc/arch/index.rst for more details.
216
217
218Board Initialisation Flow:
219--------------------------
220
221This is the intended start-up flow for boards. This should apply for both
222SPL and U-Boot proper (i.e. they both follow the same rules).
223
224Note: "SPL" stands for "Secondary Program Loader," which is explained in
225more detail later in this file.
226
227At present, SPL mostly uses a separate code path, but the function names
228and roles of each function are the same. Some boards or architectures
229may not conform to this.  At least most ARM boards which use
230CONFIG_SPL_FRAMEWORK conform to this.
231
232Execution typically starts with an architecture-specific (and possibly
233CPU-specific) start.S file, such as:
234
235	- arch/arm/cpu/armv7/start.S
236	- arch/powerpc/cpu/mpc83xx/start.S
237	- arch/mips/cpu/start.S
238
239and so on. From there, three functions are called; the purpose and
240limitations of each of these functions are described below.
241
242lowlevel_init():
243	- purpose: essential init to permit execution to reach board_init_f()
244	- no global_data or BSS
245	- there is no stack (ARMv7 may have one but it will soon be removed)
246	- must not set up SDRAM or use console
247	- must only do the bare minimum to allow execution to continue to
248		board_init_f()
249	- this is almost never needed
250	- return normally from this function
251
252board_init_f():
253	- purpose: set up the machine ready for running board_init_r():
254		i.e. SDRAM and serial UART
255	- global_data is available
256	- stack is in SRAM
257	- BSS is not available, so you cannot use global/static variables,
258		only stack variables and global_data
259
260	Non-SPL-specific notes:
261	- dram_init() is called to set up DRAM. If already done in SPL this
262		can do nothing
263
264	SPL-specific notes:
265	- you can override the entire board_init_f() function with your own
266		version as needed.
267	- preloader_console_init() can be called here in extremis
268	- should set up SDRAM, and anything needed to make the UART work
269	- these is no need to clear BSS, it will be done by crt0.S
270	- for specific scenarios on certain architectures an early BSS *can*
271	  be made available (via CONFIG_SPL_EARLY_BSS by moving the clearing
272	  of BSS prior to entering board_init_f()) but doing so is discouraged.
273	  Instead it is strongly recommended to architect any code changes
274	  or additions such to not depend on the availability of BSS during
275	  board_init_f() as indicated in other sections of this README to
276	  maintain compatibility and consistency across the entire code base.
277	- must return normally from this function (don't call board_init_r()
278		directly)
279
280Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
281this point the stack and global_data are relocated to below
282CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
283memory.
284
285board_init_r():
286	- purpose: main execution, common code
287	- global_data is available
288	- SDRAM is available
289	- BSS is available, all static/global variables can be used
290	- execution eventually continues to main_loop()
291
292	Non-SPL-specific notes:
293	- U-Boot is relocated to the top of memory and is now running from
294		there.
295
296	SPL-specific notes:
297	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
298		CONFIG_SPL_STACK_R_ADDR points into SDRAM
299	- preloader_console_init() can be called here - typically this is
300		done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
301		spl_board_init() function containing this call
302	- loads U-Boot or (in falcon mode) Linux
303
304
305
306Configuration Options:
307----------------------
308
309Configuration depends on the combination of board and CPU type; all
310such information is kept in a configuration file
311"include/configs/<board_name>.h".
312
313Example: For a TQM823L module, all configuration settings are in
314"include/configs/TQM823L.h".
315
316
317Many of the options are named exactly as the corresponding Linux
318kernel configuration options. The intention is to make it easier to
319build a config tool - later.
320
321- ARM Platform Bus Type(CCI):
322		CoreLink Cache Coherent Interconnect (CCI) is ARM BUS which
323		provides full cache coherency between two clusters of multi-core
324		CPUs and I/O coherency for devices and I/O masters
325
326		CONFIG_SYS_FSL_HAS_CCI400
327
328		Defined For SoC that has cache coherent interconnect
329		CCN-400
330
331		CONFIG_SYS_FSL_HAS_CCN504
332
333		Defined for SoC that has cache coherent interconnect CCN-504
334
335The following options need to be configured:
336
337- CPU Type:	Define exactly one, e.g. CONFIG_MPC85XX.
338
339- Board Type:	Define exactly one, e.g. CONFIG_MPC8540ADS.
340
341- 85xx CPU Options:
342		CONFIG_SYS_PPC64
343
344		Specifies that the core is a 64-bit PowerPC implementation (implements
345		the "64" category of the Power ISA). This is necessary for ePAPR
346		compliance, among other possible reasons.
347
348		CONFIG_SYS_FSL_TBCLK_DIV
349
350		Defines the core time base clock divider ratio compared to the
351		system clock.  On most PQ3 devices this is 8, on newer QorIQ
352		devices it can be 16 or 32.  The ratio varies from SoC to Soc.
353
354		CONFIG_SYS_FSL_PCIE_COMPAT
355
356		Defines the string to utilize when trying to match PCIe device
357		tree nodes for the given platform.
358
359		CONFIG_SYS_FSL_ERRATUM_A004510
360
361		Enables a workaround for erratum A004510.  If set,
362		then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
363		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
364
365		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
366		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
367
368		Defines one or two SoC revisions (low 8 bits of SVR)
369		for which the A004510 workaround should be applied.
370
371		The rest of SVR is either not relevant to the decision
372		of whether the erratum is present (e.g. p2040 versus
373		p2041) or is implied by the build target, which controls
374		whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
375
376		See Freescale App Note 4493 for more information about
377		this erratum.
378
379		CONFIG_A003399_NOR_WORKAROUND
380		Enables a workaround for IFC erratum A003399. It is only
381		required during NOR boot.
382
383		CONFIG_A008044_WORKAROUND
384		Enables a workaround for T1040/T1042 erratum A008044. It is only
385		required during NAND boot and valid for Rev 1.0 SoC revision
386
387		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
388
389		This is the value to write into CCSR offset 0x18600
390		according to the A004510 workaround.
391
392		CONFIG_SYS_FSL_DSP_DDR_ADDR
393		This value denotes start offset of DDR memory which is
394		connected exclusively to the DSP cores.
395
396		CONFIG_SYS_FSL_DSP_M2_RAM_ADDR
397		This value denotes start offset of M2 memory
398		which is directly connected to the DSP core.
399
400		CONFIG_SYS_FSL_DSP_M3_RAM_ADDR
401		This value denotes start offset of M3 memory which is directly
402		connected to the DSP core.
403
404		CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
405		This value denotes start offset of DSP CCSR space.
406
407		CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
408		Single Source Clock is clocking mode present in some of FSL SoC's.
409		In this mode, a single differential clock is used to supply
410		clocks to the sysclock, ddrclock and usbclock.
411
412		CONFIG_SYS_CPC_REINIT_F
413		This CONFIG is defined when the CPC is configured as SRAM at the
414		time of U-Boot entry and is required to be re-initialized.
415
416		CONFIG_DEEP_SLEEP
417		Indicates this SoC supports deep sleep feature. If deep sleep is
418		supported, core will start to execute uboot when wakes up.
419
420- Generic CPU options:
421		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN
422
423		Defines the endianess of the CPU. Implementation of those
424		values is arch specific.
425
426		CONFIG_SYS_FSL_DDR
427		Freescale DDR driver in use. This type of DDR controller is
428		found in mpc83xx, mpc85xx, mpc86xx as well as some ARM core
429		SoCs.
430
431		CONFIG_SYS_FSL_DDR_ADDR
432		Freescale DDR memory-mapped register base.
433
434		CONFIG_SYS_FSL_DDR_EMU
435		Specify emulator support for DDR. Some DDR features such as
436		deskew training are not available.
437
438		CONFIG_SYS_FSL_DDRC_GEN1
439		Freescale DDR1 controller.
440
441		CONFIG_SYS_FSL_DDRC_GEN2
442		Freescale DDR2 controller.
443
444		CONFIG_SYS_FSL_DDRC_GEN3
445		Freescale DDR3 controller.
446
447		CONFIG_SYS_FSL_DDRC_GEN4
448		Freescale DDR4 controller.
449
450		CONFIG_SYS_FSL_DDRC_ARM_GEN3
451		Freescale DDR3 controller for ARM-based SoCs.
452
453		CONFIG_SYS_FSL_DDR1
454		Board config to use DDR1. It can be enabled for SoCs with
455		Freescale DDR1 or DDR2 controllers, depending on the board
456		implemetation.
457
458		CONFIG_SYS_FSL_DDR2
459		Board config to use DDR2. It can be enabled for SoCs with
460		Freescale DDR2 or DDR3 controllers, depending on the board
461		implementation.
462
463		CONFIG_SYS_FSL_DDR3
464		Board config to use DDR3. It can be enabled for SoCs with
465		Freescale DDR3 or DDR3L controllers.
466
467		CONFIG_SYS_FSL_DDR3L
468		Board config to use DDR3L. It can be enabled for SoCs with
469		DDR3L controllers.
470
471		CONFIG_SYS_FSL_DDR4
472		Board config to use DDR4. It can be enabled for SoCs with
473		DDR4 controllers.
474
475		CONFIG_SYS_FSL_IFC_BE
476		Defines the IFC controller register space as Big Endian
477
478		CONFIG_SYS_FSL_IFC_LE
479		Defines the IFC controller register space as Little Endian
480
481		CONFIG_SYS_FSL_IFC_CLK_DIV
482		Defines divider of platform clock(clock input to IFC controller).
483
484		CONFIG_SYS_FSL_LBC_CLK_DIV
485		Defines divider of platform clock(clock input to eLBC controller).
486
487		CONFIG_SYS_FSL_PBL_PBI
488		It enables addition of RCW (Power on reset configuration) in built image.
489		Please refer doc/README.pblimage for more details
490
491		CONFIG_SYS_FSL_PBL_RCW
492		It adds PBI(pre-boot instructions) commands in u-boot build image.
493		PBI commands can be used to configure SoC before it starts the execution.
494		Please refer doc/README.pblimage for more details
495
496		CONFIG_SYS_FSL_DDR_BE
497		Defines the DDR controller register space as Big Endian
498
499		CONFIG_SYS_FSL_DDR_LE
500		Defines the DDR controller register space as Little Endian
501
502		CONFIG_SYS_FSL_DDR_SDRAM_BASE_PHY
503		Physical address from the view of DDR controllers. It is the
504		same as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. But
505		it could be different for ARM SoCs.
506
507		CONFIG_SYS_FSL_DDR_INTLV_256B
508		DDR controller interleaving on 256-byte. This is a special
509		interleaving mode, handled by Dickens for Freescale layerscape
510		SoCs with ARM core.
511
512		CONFIG_SYS_FSL_DDR_MAIN_NUM_CTRLS
513		Number of controllers used as main memory.
514
515		CONFIG_SYS_FSL_OTHER_DDR_NUM_CTRLS
516		Number of controllers used for other than main memory.
517
518		CONFIG_SYS_FSL_HAS_DP_DDR
519		Defines the SoC has DP-DDR used for DPAA.
520
521		CONFIG_SYS_FSL_SEC_BE
522		Defines the SEC controller register space as Big Endian
523
524		CONFIG_SYS_FSL_SEC_LE
525		Defines the SEC controller register space as Little Endian
526
527- MIPS CPU options:
528		CONFIG_SYS_INIT_SP_OFFSET
529
530		Offset relative to CONFIG_SYS_SDRAM_BASE for initial stack
531		pointer. This is needed for the temporary stack before
532		relocation.
533
534		CONFIG_XWAY_SWAP_BYTES
535
536		Enable compilation of tools/xway-swap-bytes needed for Lantiq
537		XWAY SoCs for booting from NOR flash. The U-Boot image needs to
538		be swapped if a flash programmer is used.
539
540- ARM options:
541		CONFIG_SYS_EXCEPTION_VECTORS_HIGH
542
543		Select high exception vectors of the ARM core, e.g., do not
544		clear the V bit of the c1 register of CP15.
545
546		COUNTER_FREQUENCY
547		Generic timer clock source frequency.
548
549		COUNTER_FREQUENCY_REAL
550		Generic timer clock source frequency if the real clock is
551		different from COUNTER_FREQUENCY, and can only be determined
552		at run time.
553
554- Tegra SoC options:
555		CONFIG_TEGRA_SUPPORT_NON_SECURE
556
557		Support executing U-Boot in non-secure (NS) mode. Certain
558		impossible actions will be skipped if the CPU is in NS mode,
559		such as ARM architectural timer initialization.
560
561- Linux Kernel Interface:
562		CONFIG_MEMSIZE_IN_BYTES		[relevant for MIPS only]
563
564		When transferring memsize parameter to Linux, some versions
565		expect it to be in bytes, others in MB.
566		Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.
567
568		CONFIG_OF_LIBFDT
569
570		New kernel versions are expecting firmware settings to be
571		passed using flattened device trees (based on open firmware
572		concepts).
573
574		CONFIG_OF_LIBFDT
575		 * New libfdt-based support
576		 * Adds the "fdt" command
577		 * The bootm command automatically updates the fdt
578
579		OF_TBCLK - The timebase frequency.
580		OF_STDOUT_PATH - The path to the console device
581
582		boards with QUICC Engines require OF_QE to set UCC MAC
583		addresses
584
585		CONFIG_OF_BOARD_SETUP
586
587		Board code has addition modification that it wants to make
588		to the flat device tree before handing it off to the kernel
589
590		CONFIG_OF_SYSTEM_SETUP
591
592		Other code has addition modification that it wants to make
593		to the flat device tree before handing it off to the kernel.
594		This causes ft_system_setup() to be called before booting
595		the kernel.
596
597		CONFIG_OF_IDE_FIXUP
598
599		U-Boot can detect if an IDE device is present or not.
600		If not, and this new config option is activated, U-Boot
601		removes the ATA node from the DTS before booting Linux,
602		so the Linux IDE driver does not probe the device and
603		crash. This is needed for buggy hardware (uc101) where
604		no pull down resistor is connected to the signal IDE5V_DD7.
605
606		CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]
607
608		This setting is mandatory for all boards that have only one
609		machine type and must be used to specify the machine type
610		number as it appears in the ARM machine registry
611		(see http://www.arm.linux.org.uk/developer/machines/).
612		Only boards that have multiple machine types supported
613		in a single configuration file and the machine type is
614		runtime discoverable, do not have to use this setting.
615
616- vxWorks boot parameters:
617
618		bootvx constructs a valid bootline using the following
619		environments variables: bootdev, bootfile, ipaddr, netmask,
620		serverip, gatewayip, hostname, othbootargs.
621		It loads the vxWorks image pointed bootfile.
622
623		Note: If a "bootargs" environment is defined, it will overwride
624		the defaults discussed just above.
625
626- Cache Configuration:
627		CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot
628
629- Cache Configuration for ARM:
630		CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
631				      controller
632		CONFIG_SYS_PL310_BASE - Physical base address of PL310
633					controller register space
634
635- Serial Ports:
636		CONFIG_PL010_SERIAL
637
638		Define this if you want support for Amba PrimeCell PL010 UARTs.
639
640		CONFIG_PL011_SERIAL
641
642		Define this if you want support for Amba PrimeCell PL011 UARTs.
643
644		CONFIG_PL011_CLOCK
645
646		If you have Amba PrimeCell PL011 UARTs, set this variable to
647		the clock speed of the UARTs.
648
649		CONFIG_PL01x_PORTS
650
651		If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
652		define this to a list of base addresses for each (supported)
653		port. See e.g. include/configs/versatile.h
654
655		CONFIG_SERIAL_HW_FLOW_CONTROL
656
657		Define this variable to enable hw flow control in serial driver.
658		Current user of this option is drivers/serial/nsl16550.c driver
659
660- Autoboot Command:
661		CONFIG_BOOTCOMMAND
662		Only needed when CONFIG_BOOTDELAY is enabled;
663		define a command string that is automatically executed
664		when no character is read on the console interface
665		within "Boot Delay" after reset.
666
667		CONFIG_RAMBOOT and CONFIG_NFSBOOT
668		The value of these goes into the environment as
669		"ramboot" and "nfsboot" respectively, and can be used
670		as a convenience, when switching between booting from
671		RAM and NFS.
672
673- Serial Download Echo Mode:
674		CONFIG_LOADS_ECHO
675		If defined to 1, all characters received during a
676		serial download (using the "loads" command) are
677		echoed back. This might be needed by some terminal
678		emulations (like "cu"), but may as well just take
679		time on others. This setting #define's the initial
680		value of the "loads_echo" environment variable.
681
682- Kgdb Serial Baudrate: (if CONFIG_CMD_KGDB is defined)
683		CONFIG_KGDB_BAUDRATE
684		Select one of the baudrates listed in
685		CONFIG_SYS_BAUDRATE_TABLE, see below.
686
687- Removal of commands
688		If no commands are needed to boot, you can disable
689		CONFIG_CMDLINE to remove them. In this case, the command line
690		will not be available, and when U-Boot wants to execute the
691		boot command (on start-up) it will call board_run_command()
692		instead. This can reduce image size significantly for very
693		simple boot procedures.
694
695- Regular expression support:
696		CONFIG_REGEX
697		If this variable is defined, U-Boot is linked against
698		the SLRE (Super Light Regular Expression) library,
699		which adds regex support to some commands, as for
700		example "env grep" and "setexpr".
701
702- Device tree:
703		CONFIG_OF_CONTROL
704		If this variable is defined, U-Boot will use a device tree
705		to configure its devices, instead of relying on statically
706		compiled #defines in the board file. This option is
707		experimental and only available on a few boards. The device
708		tree is available in the global data as gd->fdt_blob.
709
710		U-Boot needs to get its device tree from somewhere. This can
711		be done using one of the three options below:
712
713		CONFIG_OF_EMBED
714		If this variable is defined, U-Boot will embed a device tree
715		binary in its image. This device tree file should be in the
716		board directory and called <soc>-<board>.dts. The binary file
717		is then picked up in board_init_f() and made available through
718		the global data structure as gd->fdt_blob.
719
720		CONFIG_OF_SEPARATE
721		If this variable is defined, U-Boot will build a device tree
722		binary. It will be called u-boot.dtb. Architecture-specific
723		code will locate it at run-time. Generally this works by:
724
725			cat u-boot.bin u-boot.dtb >image.bin
726
727		and in fact, U-Boot does this for you, creating a file called
728		u-boot-dtb.bin which is useful in the common case. You can
729		still use the individual files if you need something more
730		exotic.
731
732		CONFIG_OF_BOARD
733		If this variable is defined, U-Boot will use the device tree
734		provided by the board at runtime instead of embedding one with
735		the image. Only boards defining board_fdt_blob_setup() support
736		this option (see include/fdtdec.h file).
737
738- Watchdog:
739		CONFIG_WATCHDOG
740		If this variable is defined, it enables watchdog
741		support for the SoC. There must be support in the SoC
742		specific code for a watchdog. For the 8xx
743		CPUs, the SIU Watchdog feature is enabled in the SYPCR
744		register.  When supported for a specific SoC is
745		available, then no further board specific code should
746		be needed to use it.
747
748		CONFIG_HW_WATCHDOG
749		When using a watchdog circuitry external to the used
750		SoC, then define this variable and provide board
751		specific code for the "hw_watchdog_reset" function.
752
753- Real-Time Clock:
754
755		When CONFIG_CMD_DATE is selected, the type of the RTC
756		has to be selected, too. Define exactly one of the
757		following options:
758
759		CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
760		CONFIG_RTC_MC13XXX	- use MC13783 or MC13892 RTC
761		CONFIG_RTC_MC146818	- use MC146818 RTC
762		CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
763		CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC
764		CONFIG_RTC_DS1338	- use Maxim, Inc. DS1338 RTC
765		CONFIG_RTC_DS1339	- use Maxim, Inc. DS1339 RTC
766		CONFIG_RTC_DS164x	- use Dallas DS164x RTC
767		CONFIG_RTC_ISL1208	- use Intersil ISL1208 RTC
768		CONFIG_RTC_MAX6900	- use Maxim, Inc. MAX6900 RTC
769		CONFIG_RTC_DS1337_NOOSC	- Turn off the OSC output for DS1337
770		CONFIG_SYS_RV3029_TCR	- enable trickle charger on
771					  RV3029 RTC.
772
773		Note that if the RTC uses I2C, then the I2C interface
774		must also be configured. See I2C Support, below.
775
776- GPIO Support:
777		CONFIG_PCA953X		- use NXP's PCA953X series I2C GPIO
778
779		The CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list of
780		chip-ngpio pairs that tell the PCA953X driver the number of
781		pins supported by a particular chip.
782
783		Note that if the GPIO device uses I2C, then the I2C interface
784		must also be configured. See I2C Support, below.
785
786- I/O tracing:
787		When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
788		accesses and can checksum them or write a list of them out
789		to memory. See the 'iotrace' command for details. This is
790		useful for testing device drivers since it can confirm that
791		the driver behaves the same way before and after a code
792		change. Currently this is supported on sandbox and arm. To
793		add support for your architecture, add '#include <iotrace.h>'
794		to the bottom of arch/<arch>/include/asm/io.h and test.
795
796		Example output from the 'iotrace stats' command is below.
797		Note that if the trace buffer is exhausted, the checksum will
798		still continue to operate.
799
800			iotrace is enabled
801			Start:  10000000	(buffer start address)
802			Size:   00010000	(buffer size)
803			Offset: 00000120	(current buffer offset)
804			Output: 10000120	(start + offset)
805			Count:  00000018	(number of trace records)
806			CRC32:  9526fb66	(CRC32 of all trace records)
807
808- Timestamp Support:
809
810		When CONFIG_TIMESTAMP is selected, the timestamp
811		(date and time) of an image is printed by image
812		commands like bootm or iminfo. This option is
813		automatically enabled when you select CONFIG_CMD_DATE .
814
815- Partition Labels (disklabels) Supported:
816		Zero or more of the following:
817		CONFIG_MAC_PARTITION   Apple's MacOS partition table.
818		CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.
819		CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the
820				       bootloader.  Note 2TB partition limit; see
821				       disk/part_efi.c
822		CONFIG_SCSI) you must configure support for at
823		least one non-MTD partition type as well.
824
825- IDE Reset method:
826		CONFIG_IDE_RESET_ROUTINE - this is defined in several
827		board configurations files but used nowhere!
828
829		CONFIG_IDE_RESET - is this is defined, IDE Reset will
830		be performed by calling the function
831			ide_set_reset(int reset)
832		which has to be defined in a board specific file
833
834- ATAPI Support:
835		CONFIG_ATAPI
836
837		Set this to enable ATAPI support.
838
839- LBA48 Support
840		CONFIG_LBA48
841
842		Set this to enable support for disks larger than 137GB
843		Also look at CONFIG_SYS_64BIT_LBA.
844		Whithout these , LBA48 support uses 32bit variables and will 'only'
845		support disks up to 2.1TB.
846
847		CONFIG_SYS_64BIT_LBA:
848			When enabled, makes the IDE subsystem use 64bit sector addresses.
849			Default is 32bit.
850
851- SCSI Support:
852		CONFIG_SYS_SCSI_MAX_LUN [8], CONFIG_SYS_SCSI_MAX_SCSI_ID [7] and
853		CONFIG_SYS_SCSI_MAX_DEVICE [CONFIG_SYS_SCSI_MAX_SCSI_ID *
854		CONFIG_SYS_SCSI_MAX_LUN] can be adjusted to define the
855		maximum numbers of LUNs, SCSI ID's and target
856		devices.
857
858		The environment variable 'scsidevs' is set to the number of
859		SCSI devices found during the last scan.
860
861- NETWORK Support (PCI):
862		CONFIG_E1000
863		Support for Intel 8254x/8257x gigabit chips.
864
865		CONFIG_E1000_SPI
866		Utility code for direct access to the SPI bus on Intel 8257x.
867		This does not do anything useful unless you set at least one
868		of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
869
870		CONFIG_E1000_SPI_GENERIC
871		Allow generic access to the SPI bus on the Intel 8257x, for
872		example with the "sspi" command.
873
874		CONFIG_NATSEMI
875		Support for National dp83815 chips.
876
877		CONFIG_NS8382X
878		Support for National dp8382[01] gigabit chips.
879
880- NETWORK Support (other):
881
882		CONFIG_DRIVER_AT91EMAC
883		Support for AT91RM9200 EMAC.
884
885			CONFIG_RMII
886			Define this to use reduced MII inteface
887
888			CONFIG_DRIVER_AT91EMAC_QUIET
889			If this defined, the driver is quiet.
890			The driver doen't show link status messages.
891
892		CONFIG_CALXEDA_XGMAC
893		Support for the Calxeda XGMAC device
894
895		CONFIG_LAN91C96
896		Support for SMSC's LAN91C96 chips.
897
898			CONFIG_LAN91C96_USE_32_BIT
899			Define this to enable 32 bit addressing
900
901		CONFIG_SMC91111
902		Support for SMSC's LAN91C111 chip
903
904			CONFIG_SMC91111_BASE
905			Define this to hold the physical address
906			of the device (I/O space)
907
908			CONFIG_SMC_USE_32_BIT
909			Define this if data bus is 32 bits
910
911			CONFIG_SMC_USE_IOFUNCS
912			Define this to use i/o functions instead of macros
913			(some hardware wont work with macros)
914
915			CONFIG_SYS_DAVINCI_EMAC_PHY_COUNT
916			Define this if you have more then 3 PHYs.
917
918		CONFIG_FTGMAC100
919		Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
920
921			CONFIG_FTGMAC100_EGIGA
922			Define this to use GE link update with gigabit PHY.
923			Define this if FTGMAC100 is connected to gigabit PHY.
924			If your system has 10/100 PHY only, it might not occur
925			wrong behavior. Because PHY usually return timeout or
926			useless data when polling gigabit status and gigabit
927			control registers. This behavior won't affect the
928			correctnessof 10/100 link speed update.
929
930		CONFIG_SH_ETHER
931		Support for Renesas on-chip Ethernet controller
932
933			CONFIG_SH_ETHER_USE_PORT
934			Define the number of ports to be used
935
936			CONFIG_SH_ETHER_PHY_ADDR
937			Define the ETH PHY's address
938
939			CONFIG_SH_ETHER_CACHE_WRITEBACK
940			If this option is set, the driver enables cache flush.
941
942- TPM Support:
943		CONFIG_TPM
944		Support TPM devices.
945
946		CONFIG_TPM_TIS_INFINEON
947		Support for Infineon i2c bus TPM devices. Only one device
948		per system is supported at this time.
949
950			CONFIG_TPM_TIS_I2C_BURST_LIMITATION
951			Define the burst count bytes upper limit
952
953		CONFIG_TPM_ST33ZP24
954		Support for STMicroelectronics TPM devices. Requires DM_TPM support.
955
956			CONFIG_TPM_ST33ZP24_I2C
957			Support for STMicroelectronics ST33ZP24 I2C devices.
958			Requires TPM_ST33ZP24 and I2C.
959
960			CONFIG_TPM_ST33ZP24_SPI
961			Support for STMicroelectronics ST33ZP24 SPI devices.
962			Requires TPM_ST33ZP24 and SPI.
963
964		CONFIG_TPM_ATMEL_TWI
965		Support for Atmel TWI TPM device. Requires I2C support.
966
967		CONFIG_TPM_TIS_LPC
968		Support for generic parallel port TPM devices. Only one device
969		per system is supported at this time.
970
971			CONFIG_TPM_TIS_BASE_ADDRESS
972			Base address where the generic TPM device is mapped
973			to. Contemporary x86 systems usually map it at
974			0xfed40000.
975
976		CONFIG_TPM
977		Define this to enable the TPM support library which provides
978		functional interfaces to some TPM commands.
979		Requires support for a TPM device.
980
981		CONFIG_TPM_AUTH_SESSIONS
982		Define this to enable authorized functions in the TPM library.
983		Requires CONFIG_TPM and CONFIG_SHA1.
984
985- USB Support:
986		At the moment only the UHCI host controller is
987		supported (PIP405, MIP405); define
988		CONFIG_USB_UHCI to enable it.
989		define CONFIG_USB_KEYBOARD to enable the USB Keyboard
990		and define CONFIG_USB_STORAGE to enable the USB
991		storage devices.
992		Note:
993		Supported are USB Keyboards and USB Floppy drives
994		(TEAC FD-05PUB).
995
996		CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of the
997		txfilltuning field in the EHCI controller on reset.
998
999		CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
1000		HW module registers.
1001
1002- USB Device:
1003		Define the below if you wish to use the USB console.
1004		Once firmware is rebuilt from a serial console issue the
1005		command "setenv stdin usbtty; setenv stdout usbtty" and
1006		attach your USB cable. The Unix command "dmesg" should print
1007		it has found a new device. The environment variable usbtty
1008		can be set to gserial or cdc_acm to enable your device to
1009		appear to a USB host as a Linux gserial device or a
1010		Common Device Class Abstract Control Model serial device.
1011		If you select usbtty = gserial you should be able to enumerate
1012		a Linux host by
1013		# modprobe usbserial vendor=0xVendorID product=0xProductID
1014		else if using cdc_acm, simply setting the environment
1015		variable usbtty to be cdc_acm should suffice. The following
1016		might be defined in YourBoardName.h
1017
1018			CONFIG_USB_DEVICE
1019			Define this to build a UDC device
1020
1021			CONFIG_USB_TTY
1022			Define this to have a tty type of device available to
1023			talk to the UDC device
1024
1025			CONFIG_USBD_HS
1026			Define this to enable the high speed support for usb
1027			device and usbtty. If this feature is enabled, a routine
1028			int is_usbd_high_speed(void)
1029			also needs to be defined by the driver to dynamically poll
1030			whether the enumeration has succeded at high speed or full
1031			speed.
1032
1033			CONFIG_SYS_CONSOLE_IS_IN_ENV
1034			Define this if you want stdin, stdout &/or stderr to
1035			be set to usbtty.
1036
1037		If you have a USB-IF assigned VendorID then you may wish to
1038		define your own vendor specific values either in BoardName.h
1039		or directly in usbd_vendor_info.h. If you don't define
1040		CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
1041		CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
1042		should pretend to be a Linux device to it's target host.
1043
1044			CONFIG_USBD_MANUFACTURER
1045			Define this string as the name of your company for
1046			- CONFIG_USBD_MANUFACTURER "my company"
1047
1048			CONFIG_USBD_PRODUCT_NAME
1049			Define this string as the name of your product
1050			- CONFIG_USBD_PRODUCT_NAME "acme usb device"
1051
1052			CONFIG_USBD_VENDORID
1053			Define this as your assigned Vendor ID from the USB
1054			Implementors Forum. This *must* be a genuine Vendor ID
1055			to avoid polluting the USB namespace.
1056			- CONFIG_USBD_VENDORID 0xFFFF
1057
1058			CONFIG_USBD_PRODUCTID
1059			Define this as the unique Product ID
1060			for your device
1061			- CONFIG_USBD_PRODUCTID 0xFFFF
1062
1063- ULPI Layer Support:
1064		The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
1065		the generic ULPI layer. The generic layer accesses the ULPI PHY
1066		via the platform viewport, so you need both the genric layer and
1067		the viewport enabled. Currently only Chipidea/ARC based
1068		viewport is supported.
1069		To enable the ULPI layer support, define CONFIG_USB_ULPI and
1070		CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
1071		If your ULPI phy needs a different reference clock than the
1072		standard 24 MHz then you have to define CONFIG_ULPI_REF_CLK to
1073		the appropriate value in Hz.
1074
1075- MMC Support:
1076		The MMC controller on the Intel PXA is supported. To
1077		enable this define CONFIG_MMC. The MMC can be
1078		accessed from the boot prompt by mapping the device
1079		to physical memory similar to flash. Command line is
1080		enabled with CONFIG_CMD_MMC. The MMC driver also works with
1081		the FAT fs. This is enabled with CONFIG_CMD_FAT.
1082
1083		CONFIG_SH_MMCIF
1084		Support for Renesas on-chip MMCIF controller
1085
1086			CONFIG_SH_MMCIF_ADDR
1087			Define the base address of MMCIF registers
1088
1089			CONFIG_SH_MMCIF_CLK
1090			Define the clock frequency for MMCIF
1091
1092- USB Device Firmware Update (DFU) class support:
1093		CONFIG_DFU_OVER_USB
1094		This enables the USB portion of the DFU USB class
1095
1096		CONFIG_DFU_NAND
1097		This enables support for exposing NAND devices via DFU.
1098
1099		CONFIG_DFU_RAM
1100		This enables support for exposing RAM via DFU.
1101		Note: DFU spec refer to non-volatile memory usage, but
1102		allow usages beyond the scope of spec - here RAM usage,
1103		one that would help mostly the developer.
1104
1105		CONFIG_SYS_DFU_DATA_BUF_SIZE
1106		Dfu transfer uses a buffer before writing data to the
1107		raw storage device. Make the size (in bytes) of this buffer
1108		configurable. The size of this buffer is also configurable
1109		through the "dfu_bufsiz" environment variable.
1110
1111		CONFIG_SYS_DFU_MAX_FILE_SIZE
1112		When updating files rather than the raw storage device,
1113		we use a static buffer to copy the file into and then write
1114		the buffer once we've been given the whole file.  Define
1115		this to the maximum filesize (in bytes) for the buffer.
1116		Default is 4 MiB if undefined.
1117
1118		DFU_DEFAULT_POLL_TIMEOUT
1119		Poll timeout [ms], is the timeout a device can send to the
1120		host. The host must wait for this timeout before sending
1121		a subsequent DFU_GET_STATUS request to the device.
1122
1123		DFU_MANIFEST_POLL_TIMEOUT
1124		Poll timeout [ms], which the device sends to the host when
1125		entering dfuMANIFEST state. Host waits this timeout, before
1126		sending again an USB request to the device.
1127
1128- Journaling Flash filesystem support:
1129		CONFIG_JFFS2_NAND
1130		Define these for a default partition on a NAND device
1131
1132		CONFIG_SYS_JFFS2_FIRST_SECTOR,
1133		CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKS
1134		Define these for a default partition on a NOR device
1135
1136- Keyboard Support:
1137		See Kconfig help for available keyboard drivers.
1138
1139		CONFIG_KEYBOARD
1140
1141		Define this to enable a custom keyboard support.
1142		This simply calls drv_keyboard_init() which must be
1143		defined in your board-specific files. This option is deprecated
1144		and is only used by novena. For new boards, use driver model
1145		instead.
1146
1147- Video support:
1148		CONFIG_FSL_DIU_FB
1149		Enable the Freescale DIU video driver.	Reference boards for
1150		SOCs that have a DIU should define this macro to enable DIU
1151		support, and should also define these other macros:
1152
1153			CONFIG_SYS_DIU_ADDR
1154			CONFIG_VIDEO
1155			CONFIG_CFB_CONSOLE
1156			CONFIG_VIDEO_SW_CURSOR
1157			CONFIG_VGA_AS_SINGLE_DEVICE
1158			CONFIG_VIDEO_LOGO
1159			CONFIG_VIDEO_BMP_LOGO
1160
1161		The DIU driver will look for the 'video-mode' environment
1162		variable, and if defined, enable the DIU as a console during
1163		boot.  See the documentation file doc/README.video for a
1164		description of this variable.
1165
1166- LCD Support:	CONFIG_LCD
1167
1168		Define this to enable LCD support (for output to LCD
1169		display); also select one of the supported displays
1170		by defining one of these:
1171
1172		CONFIG_ATMEL_LCD:
1173
1174			HITACHI TX09D70VM1CCA, 3.5", 240x320.
1175
1176		CONFIG_NEC_NL6448AC33:
1177
1178			NEC NL6448AC33-18. Active, color, single scan.
1179
1180		CONFIG_NEC_NL6448BC20
1181
1182			NEC NL6448BC20-08. 6.5", 640x480.
1183			Active, color, single scan.
1184
1185		CONFIG_NEC_NL6448BC33_54
1186
1187			NEC NL6448BC33-54. 10.4", 640x480.
1188			Active, color, single scan.
1189
1190		CONFIG_SHARP_16x9
1191
1192			Sharp 320x240. Active, color, single scan.
1193			It isn't 16x9, and I am not sure what it is.
1194
1195		CONFIG_SHARP_LQ64D341
1196
1197			Sharp LQ64D341 display, 640x480.
1198			Active, color, single scan.
1199
1200		CONFIG_HLD1045
1201
1202			HLD1045 display, 640x480.
1203			Active, color, single scan.
1204
1205		CONFIG_OPTREX_BW
1206
1207			Optrex	 CBL50840-2 NF-FW 99 22 M5
1208			or
1209			Hitachi	 LMG6912RPFC-00T
1210			or
1211			Hitachi	 SP14Q002
1212
1213			320x240. Black & white.
1214
1215		CONFIG_LCD_ALIGNMENT
1216
1217		Normally the LCD is page-aligned (typically 4KB). If this is
1218		defined then the LCD will be aligned to this value instead.
1219		For ARM it is sometimes useful to use MMU_SECTION_SIZE
1220		here, since it is cheaper to change data cache settings on
1221		a per-section basis.
1222
1223
1224		CONFIG_LCD_ROTATION
1225
1226		Sometimes, for example if the display is mounted in portrait
1227		mode or even if it's mounted landscape but rotated by 180degree,
1228		we need to rotate our content of the display relative to the
1229		framebuffer, so that user can read the messages which are
1230		printed out.
1231		Once CONFIG_LCD_ROTATION is defined, the lcd_console will be
1232		initialized with a given rotation from "vl_rot" out of
1233		"vidinfo_t" which is provided by the board specific code.
1234		The value for vl_rot is coded as following (matching to
1235		fbcon=rotate:<n> linux-kernel commandline):
1236		0 = no rotation respectively 0 degree
1237		1 = 90 degree rotation
1238		2 = 180 degree rotation
1239		3 = 270 degree rotation
1240
1241		If CONFIG_LCD_ROTATION is not defined, the console will be
1242		initialized with 0degree rotation.
1243
1244		CONFIG_LCD_BMP_RLE8
1245
1246		Support drawing of RLE8-compressed bitmaps on the LCD.
1247
1248		CONFIG_I2C_EDID
1249
1250		Enables an 'i2c edid' command which can read EDID
1251		information over I2C from an attached LCD display.
1252
1253- Splash Screen Support: CONFIG_SPLASH_SCREEN
1254
1255		If this option is set, the environment is checked for
1256		a variable "splashimage". If found, the usual display
1257		of logo, copyright and system information on the LCD
1258		is suppressed and the BMP image at the address
1259		specified in "splashimage" is loaded instead. The
1260		console is redirected to the "nulldev", too. This
1261		allows for a "silent" boot where a splash screen is
1262		loaded very quickly after power-on.
1263
1264		CONFIG_SPLASHIMAGE_GUARD
1265
1266		If this option is set, then U-Boot will prevent the environment
1267		variable "splashimage" from being set to a problematic address
1268		(see doc/README.displaying-bmps).
1269		This option is useful for targets where, due to alignment
1270		restrictions, an improperly aligned BMP image will cause a data
1271		abort. If you think you will not have problems with unaligned
1272		accesses (for example because your toolchain prevents them)
1273		there is no need to set this option.
1274
1275		CONFIG_SPLASH_SCREEN_ALIGN
1276
1277		If this option is set the splash image can be freely positioned
1278		on the screen. Environment variable "splashpos" specifies the
1279		position as "x,y". If a positive number is given it is used as
1280		number of pixel from left/top. If a negative number is given it
1281		is used as number of pixel from right/bottom. You can also
1282		specify 'm' for centering the image.
1283
1284		Example:
1285		setenv splashpos m,m
1286			=> image at center of screen
1287
1288		setenv splashpos 30,20
1289			=> image at x = 30 and y = 20
1290
1291		setenv splashpos -10,m
1292			=> vertically centered image
1293			   at x = dspWidth - bmpWidth - 9
1294
1295- Gzip compressed BMP image support: CONFIG_VIDEO_BMP_GZIP
1296
1297		If this option is set, additionally to standard BMP
1298		images, gzipped BMP images can be displayed via the
1299		splashscreen support or the bmp command.
1300
1301- Run length encoded BMP image (RLE8) support: CONFIG_VIDEO_BMP_RLE8
1302
1303		If this option is set, 8-bit RLE compressed BMP images
1304		can be displayed via the splashscreen support or the
1305		bmp command.
1306
1307- MII/PHY support:
1308		CONFIG_PHY_CLOCK_FREQ (ppc4xx)
1309
1310		The clock frequency of the MII bus
1311
1312		CONFIG_PHY_RESET_DELAY
1313
1314		Some PHY like Intel LXT971A need extra delay after
1315		reset before any MII register access is possible.
1316		For such PHY, set this option to the usec delay
1317		required. (minimum 300usec for LXT971A)
1318
1319		CONFIG_PHY_CMD_DELAY (ppc4xx)
1320
1321		Some PHY like Intel LXT971A need extra delay after
1322		command issued before MII status register can be read
1323
1324- IP address:
1325		CONFIG_IPADDR
1326
1327		Define a default value for the IP address to use for
1328		the default Ethernet interface, in case this is not
1329		determined through e.g. bootp.
1330		(Environment variable "ipaddr")
1331
1332- Server IP address:
1333		CONFIG_SERVERIP
1334
1335		Defines a default value for the IP address of a TFTP
1336		server to contact when using the "tftboot" command.
1337		(Environment variable "serverip")
1338
1339		CONFIG_KEEP_SERVERADDR
1340
1341		Keeps the server's MAC address, in the env 'serveraddr'
1342		for passing to bootargs (like Linux's netconsole option)
1343
1344- Gateway IP address:
1345		CONFIG_GATEWAYIP
1346
1347		Defines a default value for the IP address of the
1348		default router where packets to other networks are
1349		sent to.
1350		(Environment variable "gatewayip")
1351
1352- Subnet mask:
1353		CONFIG_NETMASK
1354
1355		Defines a default value for the subnet mask (or
1356		routing prefix) which is used to determine if an IP
1357		address belongs to the local subnet or needs to be
1358		forwarded through a router.
1359		(Environment variable "netmask")
1360
1361- BOOTP Recovery Mode:
1362		CONFIG_BOOTP_RANDOM_DELAY
1363
1364		If you have many targets in a network that try to
1365		boot using BOOTP, you may want to avoid that all
1366		systems send out BOOTP requests at precisely the same
1367		moment (which would happen for instance at recovery
1368		from a power failure, when all systems will try to
1369		boot, thus flooding the BOOTP server. Defining
1370		CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
1371		inserted before sending out BOOTP requests. The
1372		following delays are inserted then:
1373
1374		1st BOOTP request:	delay 0 ... 1 sec
1375		2nd BOOTP request:	delay 0 ... 2 sec
1376		3rd BOOTP request:	delay 0 ... 4 sec
1377		4th and following
1378		BOOTP requests:		delay 0 ... 8 sec
1379
1380		CONFIG_BOOTP_ID_CACHE_SIZE
1381
1382		BOOTP packets are uniquely identified using a 32-bit ID. The
1383		server will copy the ID from client requests to responses and
1384		U-Boot will use this to determine if it is the destination of
1385		an incoming response. Some servers will check that addresses
1386		aren't in use before handing them out (usually using an ARP
1387		ping) and therefore take up to a few hundred milliseconds to
1388		respond. Network congestion may also influence the time it
1389		takes for a response to make it back to the client. If that
1390		time is too long, U-Boot will retransmit requests. In order
1391		to allow earlier responses to still be accepted after these
1392		retransmissions, U-Boot's BOOTP client keeps a small cache of
1393		IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this
1394		cache. The default is to keep IDs for up to four outstanding
1395		requests. Increasing this will allow U-Boot to accept offers
1396		from a BOOTP client in networks with unusually high latency.
1397
1398- DHCP Advanced Options:
1399		You can fine tune the DHCP functionality by defining
1400		CONFIG_BOOTP_* symbols:
1401
1402		CONFIG_BOOTP_NISDOMAIN
1403		CONFIG_BOOTP_BOOTFILESIZE
1404		CONFIG_BOOTP_NTPSERVER
1405		CONFIG_BOOTP_TIMEOFFSET
1406		CONFIG_BOOTP_VENDOREX
1407		CONFIG_BOOTP_MAY_FAIL
1408
1409		CONFIG_BOOTP_SERVERIP - TFTP server will be the serverip
1410		environment variable, not the BOOTP server.
1411
1412		CONFIG_BOOTP_MAY_FAIL - If the DHCP server is not found
1413		after the configured retry count, the call will fail
1414		instead of starting over.  This can be used to fail over
1415		to Link-local IP address configuration if the DHCP server
1416		is not available.
1417
1418		CONFIG_BOOTP_DHCP_REQUEST_DELAY
1419
1420		A 32bit value in microseconds for a delay between
1421		receiving a "DHCP Offer" and sending the "DHCP Request".
1422		This fixes a problem with certain DHCP servers that don't
1423		respond 100% of the time to a "DHCP request". E.g. On an
1424		AT91RM9200 processor running at 180MHz, this delay needed
1425		to be *at least* 15,000 usec before a Windows Server 2003
1426		DHCP server would reply 100% of the time. I recommend at
1427		least 50,000 usec to be safe. The alternative is to hope
1428		that one of the retries will be successful but note that
1429		the DHCP timeout and retry process takes a longer than
1430		this delay.
1431
1432 - Link-local IP address negotiation:
1433		Negotiate with other link-local clients on the local network
1434		for an address that doesn't require explicit configuration.
1435		This is especially useful if a DHCP server cannot be guaranteed
1436		to exist in all environments that the device must operate.
1437
1438		See doc/README.link-local for more information.
1439
1440 - MAC address from environment variables
1441
1442		FDT_SEQ_MACADDR_FROM_ENV
1443
1444		Fix-up device tree with MAC addresses fetched sequentially from
1445		environment variables. This config work on assumption that
1446		non-usable ethernet node of device-tree are either not present
1447		or their status has been marked as "disabled".
1448
1449 - CDP Options:
1450		CONFIG_CDP_DEVICE_ID
1451
1452		The device id used in CDP trigger frames.
1453
1454		CONFIG_CDP_DEVICE_ID_PREFIX
1455
1456		A two character string which is prefixed to the MAC address
1457		of the device.
1458
1459		CONFIG_CDP_PORT_ID
1460
1461		A printf format string which contains the ascii name of
1462		the port. Normally is set to "eth%d" which sets
1463		eth0 for the first Ethernet, eth1 for the second etc.
1464
1465		CONFIG_CDP_CAPABILITIES
1466
1467		A 32bit integer which indicates the device capabilities;
1468		0x00000010 for a normal host which does not forwards.
1469
1470		CONFIG_CDP_VERSION
1471
1472		An ascii string containing the version of the software.
1473
1474		CONFIG_CDP_PLATFORM
1475
1476		An ascii string containing the name of the platform.
1477
1478		CONFIG_CDP_TRIGGER
1479
1480		A 32bit integer sent on the trigger.
1481
1482		CONFIG_CDP_POWER_CONSUMPTION
1483
1484		A 16bit integer containing the power consumption of the
1485		device in .1 of milliwatts.
1486
1487		CONFIG_CDP_APPLIANCE_VLAN_TYPE
1488
1489		A byte containing the id of the VLAN.
1490
1491- Status LED:	CONFIG_LED_STATUS
1492
1493		Several configurations allow to display the current
1494		status using a LED. For instance, the LED will blink
1495		fast while running U-Boot code, stop blinking as
1496		soon as a reply to a BOOTP request was received, and
1497		start blinking slow once the Linux kernel is running
1498		(supported by a status LED driver in the Linux
1499		kernel). Defining CONFIG_LED_STATUS enables this
1500		feature in U-Boot.
1501
1502		Additional options:
1503
1504		CONFIG_LED_STATUS_GPIO
1505		The status LED can be connected to a GPIO pin.
1506		In such cases, the gpio_led driver can be used as a
1507		status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
1508		to include the gpio_led driver in the U-Boot binary.
1509
1510		CONFIG_GPIO_LED_INVERTED_TABLE
1511		Some GPIO connected LEDs may have inverted polarity in which
1512		case the GPIO high value corresponds to LED off state and
1513		GPIO low value corresponds to LED on state.
1514		In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
1515		with a list of GPIO LEDs that have inverted polarity.
1516
1517- I2C Support:	CONFIG_SYS_I2C
1518
1519		This enable the NEW i2c subsystem, and will allow you to use
1520		i2c commands at the u-boot command line (as long as you set
1521		    CONFIG_SYS_I2C_SOFT_SPEED and CONFIG_SYS_I2C_SOFT_SLAVE
1522		    for defining speed and slave address
1523		  - activate second bus with I2C_SOFT_DECLARATIONS2 define
1524		    CONFIG_SYS_I2C_SOFT_SPEED_2 and CONFIG_SYS_I2C_SOFT_SLAVE_2
1525		    for defining speed and slave address
1526		  - activate third bus with I2C_SOFT_DECLARATIONS3 define
1527		    CONFIG_SYS_I2C_SOFT_SPEED_3 and CONFIG_SYS_I2C_SOFT_SLAVE_3
1528		    for defining speed and slave address
1529		  - activate fourth bus with I2C_SOFT_DECLARATIONS4 define
1530		    CONFIG_SYS_I2C_SOFT_SPEED_4 and CONFIG_SYS_I2C_SOFT_SLAVE_4
1531		    for defining speed and slave address
1532
1533		- drivers/i2c/fsl_i2c.c:
1534		  - activate i2c driver with CONFIG_SYS_I2C_FSL
1535		    define CONFIG_SYS_FSL_I2C_OFFSET for setting the register
1536		    offset CONFIG_SYS_FSL_I2C_SPEED for the i2c speed and
1537		    CONFIG_SYS_FSL_I2C_SLAVE for the slave addr of the first
1538		    bus.
1539		  - If your board supports a second fsl i2c bus, define
1540		    CONFIG_SYS_FSL_I2C2_OFFSET for the register offset
1541		    CONFIG_SYS_FSL_I2C2_SPEED for the speed and
1542		    CONFIG_SYS_FSL_I2C2_SLAVE for the slave address of the
1543		    second bus.
1544
1545		- drivers/i2c/tegra_i2c.c:
1546		  - activate this driver with CONFIG_SYS_I2C_TEGRA
1547		  - This driver adds 4 i2c buses with a fix speed from
1548		    100000 and the slave addr 0!
1549
1550		- drivers/i2c/ppc4xx_i2c.c
1551		  - activate this driver with CONFIG_SYS_I2C_PPC4XX
1552		  - CONFIG_SYS_I2C_PPC4XX_CH0 activate hardware channel 0
1553		  - CONFIG_SYS_I2C_PPC4XX_CH1 activate hardware channel 1
1554
1555		- drivers/i2c/i2c_mxc.c
1556		  - activate this driver with CONFIG_SYS_I2C_MXC
1557		  - enable bus 1 with CONFIG_SYS_I2C_MXC_I2C1
1558		  - enable bus 2 with CONFIG_SYS_I2C_MXC_I2C2
1559		  - enable bus 3 with CONFIG_SYS_I2C_MXC_I2C3
1560		  - enable bus 4 with CONFIG_SYS_I2C_MXC_I2C4
1561		  - define speed for bus 1 with CONFIG_SYS_MXC_I2C1_SPEED
1562		  - define slave for bus 1 with CONFIG_SYS_MXC_I2C1_SLAVE
1563		  - define speed for bus 2 with CONFIG_SYS_MXC_I2C2_SPEED
1564		  - define slave for bus 2 with CONFIG_SYS_MXC_I2C2_SLAVE
1565		  - define speed for bus 3 with CONFIG_SYS_MXC_I2C3_SPEED
1566		  - define slave for bus 3 with CONFIG_SYS_MXC_I2C3_SLAVE
1567		  - define speed for bus 4 with CONFIG_SYS_MXC_I2C4_SPEED
1568		  - define slave for bus 4 with CONFIG_SYS_MXC_I2C4_SLAVE
1569		If those defines are not set, default value is 100000
1570		for speed, and 0 for slave.
1571
1572		- drivers/i2c/rcar_i2c.c:
1573		  - activate this driver with CONFIG_SYS_I2C_RCAR
1574		  - This driver adds 4 i2c buses
1575
1576		- drivers/i2c/sh_i2c.c:
1577		  - activate this driver with CONFIG_SYS_I2C_SH
1578		  - This driver adds from 2 to 5 i2c buses
1579
1580		  - CONFIG_SYS_I2C_SH_BASE0 for setting the register channel 0
1581		  - CONFIG_SYS_I2C_SH_SPEED0 for for the speed channel 0
1582		  - CONFIG_SYS_I2C_SH_BASE1 for setting the register channel 1
1583		  - CONFIG_SYS_I2C_SH_SPEED1 for for the speed channel 1
1584		  - CONFIG_SYS_I2C_SH_BASE2 for setting the register channel 2
1585		  - CONFIG_SYS_I2C_SH_SPEED2 for for the speed channel 2
1586		  - CONFIG_SYS_I2C_SH_BASE3 for setting the register channel 3
1587		  - CONFIG_SYS_I2C_SH_SPEED3 for for the speed channel 3
1588		  - CONFIG_SYS_I2C_SH_BASE4 for setting the register channel 4
1589		  - CONFIG_SYS_I2C_SH_SPEED4 for for the speed channel 4
1590		  - CONFIG_SYS_I2C_SH_NUM_CONTROLLERS for number of i2c buses
1591
1592		- drivers/i2c/omap24xx_i2c.c
1593		  - activate this driver with CONFIG_SYS_I2C_OMAP24XX
1594		  - CONFIG_SYS_OMAP24_I2C_SPEED speed channel 0
1595		  - CONFIG_SYS_OMAP24_I2C_SLAVE slave addr channel 0
1596		  - CONFIG_SYS_OMAP24_I2C_SPEED1 speed channel 1
1597		  - CONFIG_SYS_OMAP24_I2C_SLAVE1 slave addr channel 1
1598		  - CONFIG_SYS_OMAP24_I2C_SPEED2 speed channel 2
1599		  - CONFIG_SYS_OMAP24_I2C_SLAVE2 slave addr channel 2
1600		  - CONFIG_SYS_OMAP24_I2C_SPEED3 speed channel 3
1601		  - CONFIG_SYS_OMAP24_I2C_SLAVE3 slave addr channel 3
1602		  - CONFIG_SYS_OMAP24_I2C_SPEED4 speed channel 4
1603		  - CONFIG_SYS_OMAP24_I2C_SLAVE4 slave addr channel 4
1604
1605		- drivers/i2c/s3c24x0_i2c.c:
1606		  - activate this driver with CONFIG_SYS_I2C_S3C24X0
1607		  - This driver adds i2c buses (11 for Exynos5250, Exynos5420
1608		    9 i2c buses for Exynos4 and 1 for S3C24X0 SoCs from Samsung)
1609		    with a fix speed from 100000 and the slave addr 0!
1610
1611		- drivers/i2c/ihs_i2c.c
1612		  - activate this driver with CONFIG_SYS_I2C_IHS
1613		  - CONFIG_SYS_I2C_IHS_CH0 activate hardware channel 0
1614		  - CONFIG_SYS_I2C_IHS_SPEED_0 speed channel 0
1615		  - CONFIG_SYS_I2C_IHS_SLAVE_0 slave addr channel 0
1616		  - CONFIG_SYS_I2C_IHS_CH1 activate hardware channel 1
1617		  - CONFIG_SYS_I2C_IHS_SPEED_1 speed channel 1
1618		  - CONFIG_SYS_I2C_IHS_SLAVE_1 slave addr channel 1
1619		  - CONFIG_SYS_I2C_IHS_CH2 activate hardware channel 2
1620		  - CONFIG_SYS_I2C_IHS_SPEED_2 speed channel 2
1621		  - CONFIG_SYS_I2C_IHS_SLAVE_2 slave addr channel 2
1622		  - CONFIG_SYS_I2C_IHS_CH3 activate hardware channel 3
1623		  - CONFIG_SYS_I2C_IHS_SPEED_3 speed channel 3
1624		  - CONFIG_SYS_I2C_IHS_SLAVE_3 slave addr channel 3
1625		  - activate dual channel with CONFIG_SYS_I2C_IHS_DUAL
1626		  - CONFIG_SYS_I2C_IHS_SPEED_0_1 speed channel 0_1
1627		  - CONFIG_SYS_I2C_IHS_SLAVE_0_1 slave addr channel 0_1
1628		  - CONFIG_SYS_I2C_IHS_SPEED_1_1 speed channel 1_1
1629		  - CONFIG_SYS_I2C_IHS_SLAVE_1_1 slave addr channel 1_1
1630		  - CONFIG_SYS_I2C_IHS_SPEED_2_1 speed channel 2_1
1631		  - CONFIG_SYS_I2C_IHS_SLAVE_2_1 slave addr channel 2_1
1632		  - CONFIG_SYS_I2C_IHS_SPEED_3_1 speed channel 3_1
1633		  - CONFIG_SYS_I2C_IHS_SLAVE_3_1 slave addr channel 3_1
1634
1635		additional defines:
1636
1637		CONFIG_SYS_NUM_I2C_BUSES
1638		Hold the number of i2c buses you want to use.
1639
1640		CONFIG_SYS_I2C_DIRECT_BUS
1641		define this, if you don't use i2c muxes on your hardware.
1642		if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
1643		omit this define.
1644
1645		CONFIG_SYS_I2C_MAX_HOPS
1646		define how many muxes are maximal consecutively connected
1647		on one i2c bus. If you not use i2c muxes, omit this
1648		define.
1649
1650		CONFIG_SYS_I2C_BUSES
1651		hold a list of buses you want to use, only used if
1652		CONFIG_SYS_I2C_DIRECT_BUS is not defined, for example
1653		a board with CONFIG_SYS_I2C_MAX_HOPS = 1 and
1654		CONFIG_SYS_NUM_I2C_BUSES = 9:
1655
1656		 CONFIG_SYS_I2C_BUSES	{{0, {I2C_NULL_HOP}}, \
1657					{0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
1658					{0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
1659					{0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
1660					{0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
1661					{0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
1662					{1, {I2C_NULL_HOP}}, \
1663					{1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
1664					{1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
1665					}
1666
1667		which defines
1668			bus 0 on adapter 0 without a mux
1669			bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
1670			bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
1671			bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
1672			bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
1673			bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
1674			bus 6 on adapter 1 without a mux
1675			bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
1676			bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
1677
1678		If you do not have i2c muxes on your board, omit this define.
1679
1680- Legacy I2C Support:
1681		If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
1682		then the following macros need to be defined (examples are
1683		from include/configs/lwmon.h):
1684
1685		I2C_INIT
1686
1687		(Optional). Any commands necessary to enable the I2C
1688		controller or configure ports.
1689
1690		eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=	PB_SCL)
1691
1692		I2C_ACTIVE
1693
1694		The code necessary to make the I2C data line active
1695		(driven).  If the data line is open collector, this
1696		define can be null.
1697
1698		eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)
1699
1700		I2C_TRISTATE
1701
1702		The code necessary to make the I2C data line tri-stated
1703		(inactive).  If the data line is open collector, this
1704		define can be null.
1705
1706		eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
1707
1708		I2C_READ
1709
1710		Code that returns true if the I2C data line is high,
1711		false if it is low.
1712
1713		eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
1714
1715		I2C_SDA(bit)
1716
1717		If <bit> is true, sets the I2C data line high. If it
1718		is false, it clears it (low).
1719
1720		eg: #define I2C_SDA(bit) \
1721			if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
1722			else	immr->im_cpm.cp_pbdat &= ~PB_SDA
1723
1724		I2C_SCL(bit)
1725
1726		If <bit> is true, sets the I2C clock line high. If it
1727		is false, it clears it (low).
1728
1729		eg: #define I2C_SCL(bit) \
1730			if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
1731			else	immr->im_cpm.cp_pbdat &= ~PB_SCL
1732
1733		I2C_DELAY
1734
1735		This delay is invoked four times per clock cycle so this
1736		controls the rate of data transfer.  The data rate thus
1737		is 1 / (I2C_DELAY * 4). Often defined to be something
1738		like:
1739
1740		#define I2C_DELAY  udelay(2)
1741
1742		CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
1743
1744		If your arch supports the generic GPIO framework (asm/gpio.h),
1745		then you may alternatively define the two GPIOs that are to be
1746		used as SCL / SDA.  Any of the previous I2C_xxx macros will
1747		have GPIO-based defaults assigned to them as appropriate.
1748
1749		You should define these to the GPIO value as given directly to
1750		the generic GPIO functions.
1751
1752		CONFIG_SYS_I2C_INIT_BOARD
1753
1754		When a board is reset during an i2c bus transfer
1755		chips might think that the current transfer is still
1756		in progress. On some boards it is possible to access
1757		the i2c SCLK line directly, either by using the
1758		processor pin as a GPIO or by having a second pin
1759		connected to the bus. If this option is defined a
1760		custom i2c_init_board() routine in boards/xxx/board.c
1761		is run early in the boot sequence.
1762
1763		CONFIG_I2C_MULTI_BUS
1764
1765		This option allows the use of multiple I2C buses, each of which
1766		must have a controller.	 At any point in time, only one bus is
1767		active.	 To switch to a different bus, use the 'i2c dev' command.
1768		Note that bus numbering is zero-based.
1769
1770		CONFIG_SYS_I2C_NOPROBES
1771
1772		This option specifies a list of I2C devices that will be skipped
1773		when the 'i2c probe' command is issued.	 If CONFIG_I2C_MULTI_BUS
1774		is set, specify a list of bus-device pairs.  Otherwise, specify
1775		a 1D array of device addresses
1776
1777		e.g.
1778			#undef	CONFIG_I2C_MULTI_BUS
1779			#define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}
1780
1781		will skip addresses 0x50 and 0x68 on a board with one I2C bus
1782
1783			#define CONFIG_I2C_MULTI_BUS
1784			#define CONFIG_SYS_I2C_NOPROBES	{{0,0x50},{0,0x68},{1,0x54}}
1785
1786		will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1
1787
1788		CONFIG_SYS_SPD_BUS_NUM
1789
1790		If defined, then this indicates the I2C bus number for DDR SPD.
1791		If not defined, then U-Boot assumes that SPD is on I2C bus 0.
1792
1793		CONFIG_SYS_RTC_BUS_NUM
1794
1795		If defined, then this indicates the I2C bus number for the RTC.
1796		If not defined, then U-Boot assumes that RTC is on I2C bus 0.
1797
1798		CONFIG_SOFT_I2C_READ_REPEATED_START
1799
1800		defining this will force the i2c_read() function in
1801		the soft_i2c driver to perform an I2C repeated start
1802		between writing the address pointer and reading the
1803		data.  If this define is omitted the default behaviour
1804		of doing a stop-start sequence will be used.  Most I2C
1805		devices can use either method, but some require one or
1806		the other.
1807
1808- SPI Support:	CONFIG_SPI
1809
1810		Enables SPI driver (so far only tested with
1811		SPI EEPROM, also an instance works with Crystal A/D and
1812		D/As on the SACSng board)
1813
1814		CONFIG_SOFT_SPI
1815
1816		Enables a software (bit-bang) SPI driver rather than
1817		using hardware support. This is a general purpose
1818		driver that only requires three general I/O port pins
1819		(two outputs, one input) to function. If this is
1820		defined, the board configuration must define several
1821		SPI configuration items (port pins to use, etc). For
1822		an example, see include/configs/sacsng.h.
1823
1824		CONFIG_SYS_SPI_MXC_WAIT
1825		Timeout for waiting until spi transfer completed.
1826		default: (CONFIG_SYS_HZ/100)     /* 10 ms */
1827
1828- FPGA Support: CONFIG_FPGA
1829
1830		Enables FPGA subsystem.
1831
1832		CONFIG_FPGA_<vendor>
1833
1834		Enables support for specific chip vendors.
1835		(ALTERA, XILINX)
1836
1837		CONFIG_FPGA_<family>
1838
1839		Enables support for FPGA family.
1840		(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
1841
1842		CONFIG_FPGA_COUNT
1843
1844		Specify the number of FPGA devices to support.
1845
1846		CONFIG_SYS_FPGA_PROG_FEEDBACK
1847
1848		Enable printing of hash marks during FPGA configuration.
1849
1850		CONFIG_SYS_FPGA_CHECK_BUSY
1851
1852		Enable checks on FPGA configuration interface busy
1853		status by the configuration function. This option
1854		will require a board or device specific function to
1855		be written.
1856
1857		CONFIG_FPGA_DELAY
1858
1859		If defined, a function that provides delays in the FPGA
1860		configuration driver.
1861
1862		CONFIG_SYS_FPGA_CHECK_CTRLC
1863		Allow Control-C to interrupt FPGA configuration
1864
1865		CONFIG_SYS_FPGA_CHECK_ERROR
1866
1867		Check for configuration errors during FPGA bitfile
1868		loading. For example, abort during Virtex II
1869		configuration if the INIT_B line goes low (which
1870		indicated a CRC error).
1871
1872		CONFIG_SYS_FPGA_WAIT_INIT
1873
1874		Maximum time to wait for the INIT_B line to de-assert
1875		after PROB_B has been de-asserted during a Virtex II
1876		FPGA configuration sequence. The default time is 500
1877		ms.
1878
1879		CONFIG_SYS_FPGA_WAIT_BUSY
1880
1881		Maximum time to wait for BUSY to de-assert during
1882		Virtex II FPGA configuration. The default is 5 ms.
1883
1884		CONFIG_SYS_FPGA_WAIT_CONFIG
1885
1886		Time to wait after FPGA configuration. The default is
1887		200 ms.
1888
1889- Configuration Management:
1890
1891		CONFIG_IDENT_STRING
1892
1893		If defined, this string will be added to the U-Boot
1894		version information (U_BOOT_VERSION)
1895
1896- Vendor Parameter Protection:
1897
1898		U-Boot considers the values of the environment
1899		variables "serial#" (Board Serial Number) and
1900		"ethaddr" (Ethernet Address) to be parameters that
1901		are set once by the board vendor / manufacturer, and
1902		protects these variables from casual modification by
1903		the user. Once set, these variables are read-only,
1904		and write or delete attempts are rejected. You can
1905		change this behaviour:
1906
1907		If CONFIG_ENV_OVERWRITE is #defined in your config
1908		file, the write protection for vendor parameters is
1909		completely disabled. Anybody can change or delete
1910		these parameters.
1911
1912		Alternatively, if you define _both_ an ethaddr in the
1913		default env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default
1914		Ethernet address is installed in the environment,
1915		which can be changed exactly ONCE by the user. [The
1916		serial# is unaffected by this, i. e. it remains
1917		read-only.]
1918
1919		The same can be accomplished in a more flexible way
1920		for any variable by configuring the type of access
1921		to allow for those variables in the ".flags" variable
1922		or define CONFIG_ENV_FLAGS_LIST_STATIC.
1923
1924- Protected RAM:
1925		CONFIG_PRAM
1926
1927		Define this variable to enable the reservation of
1928		"protected RAM", i. e. RAM which is not overwritten
1929		by U-Boot. Define CONFIG_PRAM to hold the number of
1930		kB you want to reserve for pRAM. You can overwrite
1931		this default value by defining an environment
1932		variable "pram" to the number of kB you want to
1933		reserve. Note that the board info structure will
1934		still show the full amount of RAM. If pRAM is
1935		reserved, a new environment variable "mem" will
1936		automatically be defined to hold the amount of
1937		remaining RAM in a form that can be passed as boot
1938		argument to Linux, for instance like that:
1939
1940			setenv bootargs ... mem=\${mem}
1941			saveenv
1942
1943		This way you can tell Linux not to use this memory,
1944		either, which results in a memory region that will
1945		not be affected by reboots.
1946
1947		*WARNING* If your board configuration uses automatic
1948		detection of the RAM size, you must make sure that
1949		this memory test is non-destructive. So far, the
1950		following board configurations are known to be
1951		"pRAM-clean":
1952
1953			IVMS8, IVML24, SPD8xx,
1954			HERMES, IP860, RPXlite, LWMON,
1955			FLAGADM
1956
1957- Access to physical memory region (> 4GB)
1958		Some basic support is provided for operations on memory not
1959		normally accessible to U-Boot - e.g. some architectures
1960		support access to more than 4GB of memory on 32-bit
1961		machines using physical address extension or similar.
1962		Define CONFIG_PHYSMEM to access this basic support, which
1963		currently only supports clearing the memory.
1964
1965- Error Recovery:
1966		CONFIG_NET_RETRY_COUNT
1967
1968		This variable defines the number of retries for
1969		network operations like ARP, RARP, TFTP, or BOOTP
1970		before giving up the operation. If not defined, a
1971		default value of 5 is used.
1972
1973		CONFIG_ARP_TIMEOUT
1974
1975		Timeout waiting for an ARP reply in milliseconds.
1976
1977		CONFIG_NFS_TIMEOUT
1978
1979		Timeout in milliseconds used in NFS protocol.
1980		If you encounter "ERROR: Cannot umount" in nfs command,
1981		try longer timeout such as
1982		#define CONFIG_NFS_TIMEOUT 10000UL
1983
1984- Command Interpreter:
1985		CONFIG_SYS_PROMPT_HUSH_PS2
1986
1987		This defines the secondary prompt string, which is
1988		printed when the command interpreter needs more input
1989		to complete a command. Usually "> ".
1990
1991	Note:
1992
1993		In the current implementation, the local variables
1994		space and global environment variables space are
1995		separated. Local variables are those you define by
1996		simply typing `name=value'. To access a local
1997		variable later on, you have write `$name' or
1998		`${name}'; to execute the contents of a variable
1999		directly type `$name' at the command prompt.
2000
2001		Global environment variables are those you use
2002		setenv/printenv to work with. To run a command stored
2003		in such a variable, you need to use the run command,
2004		and you must not use the '$' sign to access them.
2005
2006		To store commands and special characters in a
2007		variable, please use double quotation marks
2008		surrounding the whole text of the variable, instead
2009		of the backslashes before semicolons and special
2010		symbols.
2011
2012- Command Line Editing and History:
2013		CONFIG_CMDLINE_PS_SUPPORT
2014
2015		Enable support for changing the command prompt string
2016		at run-time. Only static string is supported so far.
2017		The string is obtained from environment variables PS1
2018		and PS2.
2019
2020- Default Environment:
2021		CONFIG_EXTRA_ENV_SETTINGS
2022
2023		Define this to contain any number of null terminated
2024		strings (variable = value pairs) that will be part of
2025		the default environment compiled into the boot image.
2026
2027		For example, place something like this in your
2028		board's config file:
2029
2030		#define CONFIG_EXTRA_ENV_SETTINGS \
2031			"myvar1=value1\0" \
2032			"myvar2=value2\0"
2033
2034		Warning: This method is based on knowledge about the
2035		internal format how the environment is stored by the
2036		U-Boot code. This is NOT an official, exported
2037		interface! Although it is unlikely that this format
2038		will change soon, there is no guarantee either.
2039		You better know what you are doing here.
2040
2041		Note: overly (ab)use of the default environment is
2042		discouraged. Make sure to check other ways to preset
2043		the environment like the "source" command or the
2044		boot command first.
2045
2046		CONFIG_DELAY_ENVIRONMENT
2047
2048		Normally the environment is loaded when the board is
2049		initialised so that it is available to U-Boot. This inhibits
2050		that so that the environment is not available until
2051		explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
2052		this is instead controlled by the value of
2053		/config/load-environment.
2054
2055- TFTP Fixed UDP Port:
2056		CONFIG_TFTP_PORT
2057
2058		If this is defined, the environment variable tftpsrcp
2059		is used to supply the TFTP UDP source port value.
2060		If tftpsrcp isn't defined, the normal pseudo-random port
2061		number generator is used.
2062
2063		Also, the environment variable tftpdstp is used to supply
2064		the TFTP UDP destination port value.  If tftpdstp isn't
2065		defined, the normal port 69 is used.
2066
2067		The purpose for tftpsrcp is to allow a TFTP server to
2068		blindly start the TFTP transfer using the pre-configured
2069		target IP address and UDP port. This has the effect of
2070		"punching through" the (Windows XP) firewall, allowing
2071		the remainder of the TFTP transfer to proceed normally.
2072		A better solution is to properly configure the firewall,
2073		but sometimes that is not allowed.
2074
2075		CONFIG_STANDALONE_LOAD_ADDR
2076
2077		This option defines a board specific value for the
2078		address where standalone program gets loaded, thus
2079		overwriting the architecture dependent default
2080		settings.
2081
2082- Frame Buffer Address:
2083		CONFIG_FB_ADDR
2084
2085		Define CONFIG_FB_ADDR if you want to use specific
2086		address for frame buffer.  This is typically the case
2087		when using a graphics controller has separate video
2088		memory.  U-Boot will then place the frame buffer at
2089		the given address instead of dynamically reserving it
2090		in system RAM by calling lcd_setmem(), which grabs
2091		the memory for the frame buffer depending on the
2092		configured panel size.
2093
2094		Please see board_init_f function.
2095
2096- Automatic software updates via TFTP server
2097		CONFIG_UPDATE_TFTP
2098		CONFIG_UPDATE_TFTP_CNT_MAX
2099		CONFIG_UPDATE_TFTP_MSEC_MAX
2100
2101		These options enable and control the auto-update feature;
2102		for a more detailed description refer to doc/README.update.
2103
2104- MTD Support (mtdparts command, UBI support)
2105		CONFIG_MTD_UBI_WL_THRESHOLD
2106		This parameter defines the maximum difference between the highest
2107		erase counter value and the lowest erase counter value of eraseblocks
2108		of UBI devices. When this threshold is exceeded, UBI starts performing
2109		wear leveling by means of moving data from eraseblock with low erase
2110		counter to eraseblocks with high erase counter.
2111
2112		The default value should be OK for SLC NAND flashes, NOR flashes and
2113		other flashes which have eraseblock life-cycle 100000 or more.
2114		However, in case of MLC NAND flashes which typically have eraseblock
2115		life-cycle less than 10000, the threshold should be lessened (e.g.,
2116		to 128 or 256, although it does not have to be power of 2).
2117
2118		default: 4096
2119
2120		CONFIG_MTD_UBI_BEB_LIMIT
2121		This option specifies the maximum bad physical eraseblocks UBI
2122		expects on the MTD device (per 1024 eraseblocks). If the
2123		underlying flash does not admit of bad eraseblocks (e.g. NOR
2124		flash), this value is ignored.
2125
2126		NAND datasheets often specify the minimum and maximum NVM
2127		(Number of Valid Blocks) for the flashes' endurance lifetime.
2128		The maximum expected bad eraseblocks per 1024 eraseblocks
2129		then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
2130		which gives 20 for most NANDs (MaxNVB is basically the total
2131		count of eraseblocks on the chip).
2132
2133		To put it differently, if this value is 20, UBI will try to
2134		reserve about 1.9% of physical eraseblocks for bad blocks
2135		handling. And that will be 1.9% of eraseblocks on the entire
2136		NAND chip, not just the MTD partition UBI attaches. This means
2137		that if you have, say, a NAND flash chip admits maximum 40 bad
2138		eraseblocks, and it is split on two MTD partitions of the same
2139		size, UBI will reserve 40 eraseblocks when attaching a
2140		partition.
2141
2142		default: 20
2143
2144		CONFIG_MTD_UBI_FASTMAP
2145		Fastmap is a mechanism which allows attaching an UBI device
2146		in nearly constant time. Instead of scanning the whole MTD device it
2147		only has to locate a checkpoint (called fastmap) on the device.
2148		The on-flash fastmap contains all information needed to attach
2149		the device. Using fastmap makes only sense on large devices where
2150		attaching by scanning takes long. UBI will not automatically install
2151		a fastmap on old images, but you can set the UBI parameter
2152		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
2153		that fastmap-enabled images are still usable with UBI implementations
2154		without	fastmap support. On typical flash devices the whole fastmap
2155		fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
2156
2157		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
2158		Set this parameter to enable fastmap automatically on images
2159		without a fastmap.
2160		default: 0
2161
2162		CONFIG_MTD_UBI_FM_DEBUG
2163		Enable UBI fastmap debug
2164		default: 0
2165
2166- SPL framework
2167		CONFIG_SPL
2168		Enable building of SPL globally.
2169
2170		CONFIG_SPL_LDSCRIPT
2171		LDSCRIPT for linking the SPL binary.
2172
2173		CONFIG_SPL_MAX_FOOTPRINT
2174		Maximum size in memory allocated to the SPL, BSS included.
2175		When defined, the linker checks that the actual memory
2176		used by SPL from _start to __bss_end does not exceed it.
2177		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2178		must not be both defined at the same time.
2179
2180		CONFIG_SPL_MAX_SIZE
2181		Maximum size of the SPL image (text, data, rodata, and
2182		linker lists sections), BSS excluded.
2183		When defined, the linker checks that the actual size does
2184		not exceed it.
2185
2186		CONFIG_SPL_RELOC_TEXT_BASE
2187		Address to relocate to.  If unspecified, this is equal to
2188		CONFIG_SPL_TEXT_BASE (i.e. no relocation is done).
2189
2190		CONFIG_SPL_BSS_START_ADDR
2191		Link address for the BSS within the SPL binary.
2192
2193		CONFIG_SPL_BSS_MAX_SIZE
2194		Maximum size in memory allocated to the SPL BSS.
2195		When defined, the linker checks that the actual memory used
2196		by SPL from __bss_start to __bss_end does not exceed it.
2197		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2198		must not be both defined at the same time.
2199
2200		CONFIG_SPL_STACK
2201		Adress of the start of the stack SPL will use
2202
2203		CONFIG_SPL_PANIC_ON_RAW_IMAGE
2204		When defined, SPL will panic() if the image it has
2205		loaded does not have a signature.
2206		Defining this is useful when code which loads images
2207		in SPL cannot guarantee that absolutely all read errors
2208		will be caught.
2209		An example is the LPC32XX MLC NAND driver, which will
2210		consider that a completely unreadable NAND block is bad,
2211		and thus should be skipped silently.
2212
2213		CONFIG_SPL_RELOC_STACK
2214		Adress of the start of the stack SPL will use after
2215		relocation.  If unspecified, this is equal to
2216		CONFIG_SPL_STACK.
2217
2218		CONFIG_SYS_SPL_MALLOC_START
2219		Starting address of the malloc pool used in SPL.
2220		When this option is set the full malloc is used in SPL and
2221		it is set up by spl_init() and before that, the simple malloc()
2222		can be used if CONFIG_SYS_MALLOC_F is defined.
2223
2224		CONFIG_SYS_SPL_MALLOC_SIZE
2225		The size of the malloc pool used in SPL.
2226
2227		CONFIG_SPL_OS_BOOT
2228		Enable booting directly to an OS from SPL.
2229		See also: doc/README.falcon
2230
2231		CONFIG_SPL_DISPLAY_PRINT
2232		For ARM, enable an optional function to print more information
2233		about the running system.
2234
2235		CONFIG_SPL_INIT_MINIMAL
2236		Arch init code should be built for a very small image
2237
2238		CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITION
2239		Partition on the MMC to load U-Boot from when the MMC is being
2240		used in raw mode
2241
2242		CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR
2243		Sector to load kernel uImage from when MMC is being
2244		used in raw mode (for Falcon mode)
2245
2246		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR,
2247		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS
2248		Sector and number of sectors to load kernel argument
2249		parameters from when MMC is being used in raw mode
2250		(for falcon mode)
2251
2252		CONFIG_SPL_FS_LOAD_PAYLOAD_NAME
2253		Filename to read to load U-Boot when reading from filesystem
2254
2255		CONFIG_SPL_FS_LOAD_KERNEL_NAME
2256		Filename to read to load kernel uImage when reading
2257		from filesystem (for Falcon mode)
2258
2259		CONFIG_SPL_FS_LOAD_ARGS_NAME
2260		Filename to read to load kernel argument parameters
2261		when reading from filesystem (for Falcon mode)
2262
2263		CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
2264		Set this for NAND SPL on PPC mpc83xx targets, so that
2265		start.S waits for the rest of the SPL to load before
2266		continuing (the hardware starts execution after just
2267		loading the first page rather than the full 4K).
2268
2269		CONFIG_SPL_SKIP_RELOCATE
2270		Avoid SPL relocation
2271
2272		CONFIG_SPL_NAND_IDENT
2273		SPL uses the chip ID list to identify the NAND flash.
2274		Requires CONFIG_SPL_NAND_BASE.
2275
2276		CONFIG_SPL_UBI
2277		Support for a lightweight UBI (fastmap) scanner and
2278		loader
2279
2280		CONFIG_SPL_NAND_RAW_ONLY
2281		Support to boot only raw u-boot.bin images. Use this only
2282		if you need to save space.
2283
2284		CONFIG_SPL_COMMON_INIT_DDR
2285		Set for common ddr init with serial presence detect in
2286		SPL binary.
2287
2288		CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
2289		CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
2290		CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
2291		CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,
2292		CONFIG_SYS_NAND_ECCBYTES
2293		Defines the size and behavior of the NAND that SPL uses
2294		to read U-Boot
2295
2296		CONFIG_SYS_NAND_U_BOOT_OFFS
2297		Location in NAND to read U-Boot from
2298
2299		CONFIG_SYS_NAND_U_BOOT_DST
2300		Location in memory to load U-Boot to
2301
2302		CONFIG_SYS_NAND_U_BOOT_SIZE
2303		Size of image to load
2304
2305		CONFIG_SYS_NAND_U_BOOT_START
2306		Entry point in loaded image to jump to
2307
2308		CONFIG_SYS_NAND_HW_ECC_OOBFIRST
2309		Define this if you need to first read the OOB and then the
2310		data. This is used, for example, on davinci platforms.
2311
2312		CONFIG_SPL_RAM_DEVICE
2313		Support for running image already present in ram, in SPL binary
2314
2315		CONFIG_SPL_PAD_TO
2316		Image offset to which the SPL should be padded before appending
2317		the SPL payload. By default, this is defined as
2318		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
2319		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
2320		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
2321
2322		CONFIG_SPL_TARGET
2323		Final target image containing SPL and payload.  Some SPLs
2324		use an arch-specific makefile fragment instead, for
2325		example if more than one image needs to be produced.
2326
2327		CONFIG_SPL_FIT_PRINT
2328		Printing information about a FIT image adds quite a bit of
2329		code to SPL. So this is normally disabled in SPL. Use this
2330		option to re-enable it. This will affect the output of the
2331		bootm command when booting a FIT image.
2332
2333- TPL framework
2334		CONFIG_TPL
2335		Enable building of TPL globally.
2336
2337		CONFIG_TPL_PAD_TO
2338		Image offset to which the TPL should be padded before appending
2339		the TPL payload. By default, this is defined as
2340		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
2341		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
2342		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
2343
2344- Interrupt support (PPC):
2345
2346		There are common interrupt_init() and timer_interrupt()
2347		for all PPC archs. interrupt_init() calls interrupt_init_cpu()
2348		for CPU specific initialization. interrupt_init_cpu()
2349		should set decrementer_count to appropriate value. If
2350		CPU resets decrementer automatically after interrupt
2351		(ppc4xx) it should set decrementer_count to zero.
2352		timer_interrupt() calls timer_interrupt_cpu() for CPU
2353		specific handling. If board has watchdog / status_led
2354		/ other_activity_monitor it works automatically from
2355		general timer_interrupt().
2356
2357
2358Board initialization settings:
2359------------------------------
2360
2361During Initialization u-boot calls a number of board specific functions
2362to allow the preparation of board specific prerequisites, e.g. pin setup
2363before drivers are initialized. To enable these callbacks the
2364following configuration macros have to be defined. Currently this is
2365architecture specific, so please check arch/your_architecture/lib/board.c
2366typically in board_init_f() and board_init_r().
2367
2368- CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
2369- CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
2370- CONFIG_BOARD_LATE_INIT: Call board_late_init()
2371- CONFIG_BOARD_POSTCLK_INIT: Call board_postclk_init()
2372
2373Configuration Settings:
2374-----------------------
2375
2376- MEM_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
2377		Optionally it can be defined to support 64-bit memory commands.
2378
2379- CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
2380		undefine this when you're short of memory.
2381
2382- CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
2383		width of the commands listed in the 'help' command output.
2384
2385- CONFIG_SYS_PROMPT:	This is what U-Boot prints on the console to
2386		prompt for user input.
2387
2388- CONFIG_SYS_CBSIZE:	Buffer size for input from the Console
2389
2390- CONFIG_SYS_PBSIZE:	Buffer size for Console output
2391
2392- CONFIG_SYS_MAXARGS:	max. Number of arguments accepted for monitor commands
2393
2394- CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed to
2395		the application (usually a Linux kernel) when it is
2396		booted
2397
2398- CONFIG_SYS_BAUDRATE_TABLE:
2399		List of legal baudrate settings for this board.
2400
2401- CONFIG_SYS_MEM_RESERVE_SECURE
2402		Only implemented for ARMv8 for now.
2403		If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory
2404		is substracted from total RAM and won't be reported to OS.
2405		This memory can be used as secure memory. A variable
2406		gd->arch.secure_ram is used to track the location. In systems
2407		the RAM base is not zero, or RAM is divided into banks,
2408		this variable needs to be recalcuated to get the address.
2409
2410- CONFIG_SYS_MEM_TOP_HIDE:
2411		If CONFIG_SYS_MEM_TOP_HIDE is defined in the board config header,
2412		this specified memory area will get subtracted from the top
2413		(end) of RAM and won't get "touched" at all by U-Boot. By
2414		fixing up gd->ram_size the Linux kernel should gets passed
2415		the now "corrected" memory size and won't touch it either.
2416		This should work for arch/ppc and arch/powerpc. Only Linux
2417		board ports in arch/powerpc with bootwrapper support that
2418		recalculate the memory size from the SDRAM controller setup
2419		will have to get fixed in Linux additionally.
2420
2421		This option can be used as a workaround for the 440EPx/GRx
2422		CHIP 11 errata where the last 256 bytes in SDRAM shouldn't
2423		be touched.
2424
2425		WARNING: Please make sure that this value is a multiple of
2426		the Linux page size (normally 4k). If this is not the case,
2427		then the end address of the Linux memory will be located at a
2428		non page size aligned address and this could cause major
2429		problems.
2430
2431- CONFIG_SYS_LOADS_BAUD_CHANGE:
2432		Enable temporary baudrate change while serial download
2433
2434- CONFIG_SYS_SDRAM_BASE:
2435		Physical start address of SDRAM. _Must_ be 0 here.
2436
2437- CONFIG_SYS_FLASH_BASE:
2438		Physical start address of Flash memory.
2439
2440- CONFIG_SYS_MONITOR_BASE:
2441		Physical start address of boot monitor code (set by
2442		make config files to be same as the text base address
2443		(CONFIG_SYS_TEXT_BASE) used when linking) - same as
2444		CONFIG_SYS_FLASH_BASE when booting from flash.
2445
2446- CONFIG_SYS_MONITOR_LEN:
2447		Size of memory reserved for monitor code, used to
2448		determine _at_compile_time_ (!) if the environment is
2449		embedded within the U-Boot image, or in a separate
2450		flash sector.
2451
2452- CONFIG_SYS_MALLOC_LEN:
2453		Size of DRAM reserved for malloc() use.
2454
2455- CONFIG_SYS_MALLOC_F_LEN
2456		Size of the malloc() pool for use before relocation. If
2457		this is defined, then a very simple malloc() implementation
2458		will become available before relocation. The address is just
2459		below the global data, and the stack is moved down to make
2460		space.
2461
2462		This feature allocates regions with increasing addresses
2463		within the region. calloc() is supported, but realloc()
2464		is not available. free() is supported but does nothing.
2465		The memory will be freed (or in fact just forgotten) when
2466		U-Boot relocates itself.
2467
2468- CONFIG_SYS_MALLOC_SIMPLE
2469		Provides a simple and small malloc() and calloc() for those
2470		boards which do not use the full malloc in SPL (which is
2471		enabled with CONFIG_SYS_SPL_MALLOC_START).
2472
2473- CONFIG_SYS_NONCACHED_MEMORY:
2474		Size of non-cached memory area. This area of memory will be
2475		typically located right below the malloc() area and mapped
2476		uncached in the MMU. This is useful for drivers that would
2477		otherwise require a lot of explicit cache maintenance. For
2478		some drivers it's also impossible to properly maintain the
2479		cache. For example if the regions that need to be flushed
2480		are not a multiple of the cache-line size, *and* padding
2481		cannot be allocated between the regions to align them (i.e.
2482		if the HW requires a contiguous array of regions, and the
2483		size of each region is not cache-aligned), then a flush of
2484		one region may result in overwriting data that hardware has
2485		written to another region in the same cache-line. This can
2486		happen for example in network drivers where descriptors for
2487		buffers are typically smaller than the CPU cache-line (e.g.
2488		16 bytes vs. 32 or 64 bytes).
2489
2490		Non-cached memory is only supported on 32-bit ARM at present.
2491
2492- CONFIG_SYS_BOOTM_LEN:
2493		Normally compressed uImages are limited to an
2494		uncompressed size of 8 MBytes. If this is not enough,
2495		you can define CONFIG_SYS_BOOTM_LEN in your board config file
2496		to adjust this setting to your needs.
2497
2498- CONFIG_SYS_BOOTMAPSZ:
2499		Maximum size of memory mapped by the startup code of
2500		the Linux kernel; all data that must be processed by
2501		the Linux kernel (bd_info, boot arguments, FDT blob if
2502		used) must be put below this limit, unless "bootm_low"
2503		environment variable is defined and non-zero. In such case
2504		all data for the Linux kernel must be between "bootm_low"
2505		and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.	 The environment
2506		variable "bootm_mapsize" will override the value of
2507		CONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,
2508		then the value in "bootm_size" will be used instead.
2509
2510- CONFIG_SYS_BOOT_RAMDISK_HIGH:
2511		Enable initrd_high functionality.  If defined then the
2512		initrd_high feature is enabled and the bootm ramdisk subcommand
2513		is enabled.
2514
2515- CONFIG_SYS_BOOT_GET_CMDLINE:
2516		Enables allocating and saving kernel cmdline in space between
2517		"bootm_low" and "bootm_low" + BOOTMAPSZ.
2518
2519- CONFIG_SYS_BOOT_GET_KBD:
2520		Enables allocating and saving a kernel copy of the bd_info in
2521		space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
2522
2523- CONFIG_SYS_MAX_FLASH_BANKS:
2524		Max number of Flash memory banks
2525
2526- CONFIG_SYS_MAX_FLASH_SECT:
2527		Max number of sectors on a Flash chip
2528
2529- CONFIG_SYS_FLASH_ERASE_TOUT:
2530		Timeout for Flash erase operations (in ms)
2531
2532- CONFIG_SYS_FLASH_WRITE_TOUT:
2533		Timeout for Flash write operations (in ms)
2534
2535- CONFIG_SYS_FLASH_LOCK_TOUT
2536		Timeout for Flash set sector lock bit operation (in ms)
2537
2538- CONFIG_SYS_FLASH_UNLOCK_TOUT
2539		Timeout for Flash clear lock bits operation (in ms)
2540
2541- CONFIG_SYS_FLASH_PROTECTION
2542		If defined, hardware flash sectors protection is used
2543		instead of U-Boot software protection.
2544
2545- CONFIG_SYS_DIRECT_FLASH_TFTP:
2546
2547		Enable TFTP transfers directly to flash memory;
2548		without this option such a download has to be
2549		performed in two steps: (1) download to RAM, and (2)
2550		copy from RAM to flash.
2551
2552		The two-step approach is usually more reliable, since
2553		you can check if the download worked before you erase
2554		the flash, but in some situations (when system RAM is
2555		too limited to allow for a temporary copy of the
2556		downloaded image) this option may be very useful.
2557
2558- CONFIG_SYS_FLASH_CFI:
2559		Define if the flash driver uses extra elements in the
2560		common flash structure for storing flash geometry.
2561
2562- CONFIG_FLASH_CFI_DRIVER
2563		This option also enables the building of the cfi_flash driver
2564		in the drivers directory
2565
2566- CONFIG_FLASH_CFI_MTD
2567		This option enables the building of the cfi_mtd driver
2568		in the drivers directory. The driver exports CFI flash
2569		to the MTD layer.
2570
2571- CONFIG_SYS_FLASH_USE_BUFFER_WRITE
2572		Use buffered writes to flash.
2573
2574- CONFIG_FLASH_SPANSION_S29WS_N
2575		s29ws-n MirrorBit flash has non-standard addresses for buffered
2576		write commands.
2577
2578- CONFIG_SYS_FLASH_QUIET_TEST
2579		If this option is defined, the common CFI flash doesn't
2580		print it's warning upon not recognized FLASH banks. This
2581		is useful, if some of the configured banks are only
2582		optionally available.
2583
2584- CONFIG_FLASH_SHOW_PROGRESS
2585		If defined (must be an integer), print out countdown
2586		digits and dots.  Recommended value: 45 (9..1) for 80
2587		column displays, 15 (3..1) for 40 column displays.
2588
2589- CONFIG_FLASH_VERIFY
2590		If defined, the content of the flash (destination) is compared
2591		against the source after the write operation. An error message
2592		will be printed when the contents are not identical.
2593		Please note that this option is useless in nearly all cases,
2594		since such flash programming errors usually are detected earlier
2595		while unprotecting/erasing/programming. Please only enable
2596		this option if you really know what you are doing.
2597
2598- CONFIG_SYS_RX_ETH_BUFFER:
2599		Defines the number of Ethernet receive buffers. On some
2600		Ethernet controllers it is recommended to set this value
2601		to 8 or even higher (EEPRO100 or 405 EMAC), since all
2602		buffers can be full shortly after enabling the interface
2603		on high Ethernet traffic.
2604		Defaults to 4 if not defined.
2605
2606- CONFIG_ENV_MAX_ENTRIES
2607
2608	Maximum number of entries in the hash table that is used
2609	internally to store the environment settings. The default
2610	setting is supposed to be generous and should work in most
2611	cases. This setting can be used to tune behaviour; see
2612	lib/hashtable.c for details.
2613
2614- CONFIG_ENV_FLAGS_LIST_DEFAULT
2615- CONFIG_ENV_FLAGS_LIST_STATIC
2616	Enable validation of the values given to environment variables when
2617	calling env set.  Variables can be restricted to only decimal,
2618	hexadecimal, or boolean.  If CONFIG_CMD_NET is also defined,
2619	the variables can also be restricted to IP address or MAC address.
2620
2621	The format of the list is:
2622		type_attribute = [s|d|x|b|i|m]
2623		access_attribute = [a|r|o|c]
2624		attributes = type_attribute[access_attribute]
2625		entry = variable_name[:attributes]
2626		list = entry[,list]
2627
2628	The type attributes are:
2629		s - String (default)
2630		d - Decimal
2631		x - Hexadecimal
2632		b - Boolean ([1yYtT|0nNfF])
2633		i - IP address
2634		m - MAC address
2635
2636	The access attributes are:
2637		a - Any (default)
2638		r - Read-only
2639		o - Write-once
2640		c - Change-default
2641
2642	- CONFIG_ENV_FLAGS_LIST_DEFAULT
2643		Define this to a list (string) to define the ".flags"
2644		environment variable in the default or embedded environment.
2645
2646	- CONFIG_ENV_FLAGS_LIST_STATIC
2647		Define this to a list (string) to define validation that
2648		should be done if an entry is not found in the ".flags"
2649		environment variable.  To override a setting in the static
2650		list, simply add an entry for the same variable name to the
2651		".flags" variable.
2652
2653	If CONFIG_REGEX is defined, the variable_name above is evaluated as a
2654	regular expression. This allows multiple variables to define the same
2655	flags without explicitly listing them for each variable.
2656
2657The following definitions that deal with the placement and management
2658of environment data (variable area); in general, we support the
2659following configurations:
2660
2661- CONFIG_BUILD_ENVCRC:
2662
2663	Builds up envcrc with the target environment so that external utils
2664	may easily extract it and embed it in final U-Boot images.
2665
2666BE CAREFUL! The first access to the environment happens quite early
2667in U-Boot initialization (when we try to get the setting of for the
2668console baudrate). You *MUST* have mapped your NVRAM area then, or
2669U-Boot will hang.
2670
2671Please note that even with NVRAM we still use a copy of the
2672environment in RAM: we could work on NVRAM directly, but we want to
2673keep settings there always unmodified except somebody uses "saveenv"
2674to save the current settings.
2675
2676BE CAREFUL! For some special cases, the local device can not use
2677"saveenv" command. For example, the local device will get the
2678environment stored in a remote NOR flash by SRIO or PCIE link,
2679but it can not erase, write this NOR flash by SRIO or PCIE interface.
2680
2681- CONFIG_NAND_ENV_DST
2682
2683	Defines address in RAM to which the nand_spl code should copy the
2684	environment. If redundant environment is used, it will be copied to
2685	CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
2686
2687Please note that the environment is read-only until the monitor
2688has been relocated to RAM and a RAM copy of the environment has been
2689created; also, when using EEPROM you will have to use env_get_f()
2690until then to read environment variables.
2691
2692The environment is protected by a CRC32 checksum. Before the monitor
2693is relocated into RAM, as a result of a bad CRC you will be working
2694with the compiled-in default environment - *silently*!!! [This is
2695necessary, because the first environment variable we need is the
2696"baudrate" setting for the console - if we have a bad CRC, we don't
2697have any device yet where we could complain.]
2698
2699Note: once the monitor has been relocated, then it will complain if
2700the default environment is used; a new CRC is computed as soon as you
2701use the "saveenv" command to store a valid environment.
2702
2703- CONFIG_SYS_FAULT_ECHO_LINK_DOWN:
2704		Echo the inverted Ethernet link state to the fault LED.
2705
2706		Note: If this option is active, then CONFIG_SYS_FAULT_MII_ADDR
2707		      also needs to be defined.
2708
2709- CONFIG_SYS_FAULT_MII_ADDR:
2710		MII address of the PHY to check for the Ethernet link state.
2711
2712- CONFIG_NS16550_MIN_FUNCTIONS:
2713		Define this if you desire to only have use of the NS16550_init
2714		and NS16550_putc functions for the serial driver located at
2715		drivers/serial/ns16550.c.  This option is useful for saving
2716		space for already greatly restricted images, including but not
2717		limited to NAND_SPL configurations.
2718
2719- CONFIG_DISPLAY_BOARDINFO
2720		Display information about the board that U-Boot is running on
2721		when U-Boot starts up. The board function checkboard() is called
2722		to do this.
2723
2724- CONFIG_DISPLAY_BOARDINFO_LATE
2725		Similar to the previous option, but display this information
2726		later, once stdio is running and output goes to the LCD, if
2727		present.
2728
2729- CONFIG_BOARD_SIZE_LIMIT:
2730		Maximum size of the U-Boot image. When defined, the
2731		build system checks that the actual size does not
2732		exceed it.
2733
2734Low Level (hardware related) configuration options:
2735---------------------------------------------------
2736
2737- CONFIG_SYS_CACHELINE_SIZE:
2738		Cache Line Size of the CPU.
2739
2740- CONFIG_SYS_CCSRBAR_DEFAULT:
2741		Default (power-on reset) physical address of CCSR on Freescale
2742		PowerPC SOCs.
2743
2744- CONFIG_SYS_CCSRBAR:
2745		Virtual address of CCSR.  On a 32-bit build, this is typically
2746		the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
2747
2748- CONFIG_SYS_CCSRBAR_PHYS:
2749		Physical address of CCSR.  CCSR can be relocated to a new
2750		physical address, if desired.  In this case, this macro should
2751		be set to that address.	 Otherwise, it should be set to the
2752		same value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSR
2753		is typically relocated on 36-bit builds.  It is recommended
2754		that this macro be defined via the _HIGH and _LOW macros:
2755
2756		#define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH
2757			* 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)
2758
2759- CONFIG_SYS_CCSRBAR_PHYS_HIGH:
2760		Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.	This value is typically
2761		either 0 (32-bit build) or 0xF (36-bit build).	This macro is
2762		used in assembly code, so it must not contain typecasts or
2763		integer size suffixes (e.g. "ULL").
2764
2765- CONFIG_SYS_CCSRBAR_PHYS_LOW:
2766		Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro is
2767		used in assembly code, so it must not contain typecasts or
2768		integer size suffixes (e.g. "ULL").
2769
2770- CONFIG_SYS_CCSR_DO_NOT_RELOCATE:
2771		If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will be
2772		forced to a value that ensures that CCSR is not relocated.
2773
2774- CONFIG_IDE_AHB:
2775		Most IDE controllers were designed to be connected with PCI
2776		interface. Only few of them were designed for AHB interface.
2777		When software is doing ATA command and data transfer to
2778		IDE devices through IDE-AHB controller, some additional
2779		registers accessing to these kind of IDE-AHB controller
2780		is required.
2781
2782- CONFIG_SYS_IMMR:	Physical address of the Internal Memory.
2783		DO NOT CHANGE unless you know exactly what you're
2784		doing! (11-4) [MPC8xx systems only]
2785
2786- CONFIG_SYS_INIT_RAM_ADDR:
2787
2788		Start address of memory area that can be used for
2789		initial data and stack; please note that this must be
2790		writable memory that is working WITHOUT special
2791		initialization, i. e. you CANNOT use normal RAM which
2792		will become available only after programming the
2793		memory controller and running certain initialization
2794		sequences.
2795
2796		U-Boot uses the following memory types:
2797		- MPC8xx: IMMR (internal memory of the CPU)
2798
2799- CONFIG_SYS_GBL_DATA_OFFSET:
2800
2801		Offset of the initial data structure in the memory
2802		area defined by CONFIG_SYS_INIT_RAM_ADDR. Usually
2803		CONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initial
2804		data is located at the end of the available space
2805		(sometimes written as (CONFIG_SYS_INIT_RAM_SIZE -
2806		GENERATED_GBL_DATA_SIZE), and the initial stack is just
2807		below that area (growing from (CONFIG_SYS_INIT_RAM_ADDR +
2808		CONFIG_SYS_GBL_DATA_OFFSET) downward.
2809
2810	Note:
2811		On the MPC824X (or other systems that use the data
2812		cache for initial memory) the address chosen for
2813		CONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it must
2814		point to an otherwise UNUSED address space between
2815		the top of RAM and the start of the PCI space.
2816
2817- CONFIG_SYS_SCCR:	System Clock and reset Control Register (15-27)
2818
2819- CONFIG_SYS_OR_TIMING_SDRAM:
2820		SDRAM timing
2821
2822- CONFIG_SYS_MAMR_PTA:
2823		periodic timer for refresh
2824
2825- FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CONFIG_SYS_REMAP_OR_AM,
2826  CONFIG_SYS_PRELIM_OR_AM, CONFIG_SYS_OR_TIMING_FLASH, CONFIG_SYS_OR0_REMAP,
2827  CONFIG_SYS_OR0_PRELIM, CONFIG_SYS_BR0_PRELIM, CONFIG_SYS_OR1_REMAP, CONFIG_SYS_OR1_PRELIM,
2828  CONFIG_SYS_BR1_PRELIM:
2829		Memory Controller Definitions: BR0/1 and OR0/1 (FLASH)
2830
2831- SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE,
2832  CONFIG_SYS_OR_TIMING_SDRAM, CONFIG_SYS_OR2_PRELIM, CONFIG_SYS_BR2_PRELIM,
2833  CONFIG_SYS_OR3_PRELIM, CONFIG_SYS_BR3_PRELIM:
2834		Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM)
2835
2836- CONFIG_PCI_ENUM_ONLY
2837		Only scan through and get the devices on the buses.
2838		Don't do any setup work, presumably because someone or
2839		something has already done it, and we don't need to do it
2840		a second time.	Useful for platforms that are pre-booted
2841		by coreboot or similar.
2842
2843- CONFIG_PCI_INDIRECT_BRIDGE:
2844		Enable support for indirect PCI bridges.
2845
2846- CONFIG_SYS_SRIO:
2847		Chip has SRIO or not
2848
2849- CONFIG_SRIO1:
2850		Board has SRIO 1 port available
2851
2852- CONFIG_SRIO2:
2853		Board has SRIO 2 port available
2854
2855- CONFIG_SRIO_PCIE_BOOT_MASTER
2856		Board can support master function for Boot from SRIO and PCIE
2857
2858- CONFIG_SYS_SRIOn_MEM_VIRT:
2859		Virtual Address of SRIO port 'n' memory region
2860
2861- CONFIG_SYS_SRIOn_MEM_PHYxS:
2862		Physical Address of SRIO port 'n' memory region
2863
2864- CONFIG_SYS_SRIOn_MEM_SIZE:
2865		Size of SRIO port 'n' memory region
2866
2867- CONFIG_SYS_NAND_BUSWIDTH_16BIT
2868		Defined to tell the NAND controller that the NAND chip is using
2869		a 16 bit bus.
2870		Not all NAND drivers use this symbol.
2871		Example of drivers that use it:
2872		- drivers/mtd/nand/raw/ndfc.c
2873		- drivers/mtd/nand/raw/mxc_nand.c
2874
2875- CONFIG_SYS_NDFC_EBC0_CFG
2876		Sets the EBC0_CFG register for the NDFC. If not defined
2877		a default value will be used.
2878
2879- CONFIG_SPD_EEPROM
2880		Get DDR timing information from an I2C EEPROM. Common
2881		with pluggable memory modules such as SODIMMs
2882
2883  SPD_EEPROM_ADDRESS
2884		I2C address of the SPD EEPROM
2885
2886- CONFIG_SYS_SPD_BUS_NUM
2887		If SPD EEPROM is on an I2C bus other than the first
2888		one, specify here. Note that the value must resolve
2889		to something your driver can deal with.
2890
2891- CONFIG_SYS_DDR_RAW_TIMING
2892		Get DDR timing information from other than SPD. Common with
2893		soldered DDR chips onboard without SPD. DDR raw timing
2894		parameters are extracted from datasheet and hard-coded into
2895		header files or board specific files.
2896
2897- CONFIG_FSL_DDR_INTERACTIVE
2898		Enable interactive DDR debugging. See doc/README.fsl-ddr.
2899
2900- CONFIG_FSL_DDR_SYNC_REFRESH
2901		Enable sync of refresh for multiple controllers.
2902
2903- CONFIG_FSL_DDR_BIST
2904		Enable built-in memory test for Freescale DDR controllers.
2905
2906- CONFIG_SYS_83XX_DDR_USES_CS0
2907		Only for 83xx systems. If specified, then DDR should
2908		be configured using CS0 and CS1 instead of CS2 and CS3.
2909
2910- CONFIG_RMII
2911		Enable RMII mode for all FECs.
2912		Note that this is a global option, we can't
2913		have one FEC in standard MII mode and another in RMII mode.
2914
2915- CONFIG_CRC32_VERIFY
2916		Add a verify option to the crc32 command.
2917		The syntax is:
2918
2919		=> crc32 -v <address> <count> <crc32>
2920
2921		Where address/count indicate a memory area
2922		and crc32 is the correct crc32 which the
2923		area should have.
2924
2925- CONFIG_LOOPW
2926		Add the "loopw" memory command. This only takes effect if
2927		the memory commands are activated globally (CONFIG_CMD_MEMORY).
2928
2929- CONFIG_CMD_MX_CYCLIC
2930		Add the "mdc" and "mwc" memory commands. These are cyclic
2931		"md/mw" commands.
2932		Examples:
2933
2934		=> mdc.b 10 4 500
2935		This command will print 4 bytes (10,11,12,13) each 500 ms.
2936
2937		=> mwc.l 100 12345678 10
2938		This command will write 12345678 to address 100 all 10 ms.
2939
2940		This only takes effect if the memory commands are activated
2941		globally (CONFIG_CMD_MEMORY).
2942
2943- CONFIG_SKIP_LOWLEVEL_INIT
2944		[ARM, NDS32, MIPS, RISC-V only] If this variable is defined, then certain
2945		low level initializations (like setting up the memory
2946		controller) are omitted and/or U-Boot does not
2947		relocate itself into RAM.
2948
2949		Normally this variable MUST NOT be defined. The only
2950		exception is when U-Boot is loaded (to RAM) by some
2951		other boot loader or by a debugger which performs
2952		these initializations itself.
2953
2954- CONFIG_SKIP_LOWLEVEL_INIT_ONLY
2955		[ARM926EJ-S only] This allows just the call to lowlevel_init()
2956		to be skipped. The normal CP15 init (such as enabling the
2957		instruction cache) is still performed.
2958
2959- CONFIG_SPL_BUILD
2960		Set when the currently-running compilation is for an artifact
2961		that will end up in the SPL (as opposed to the TPL or U-Boot
2962		proper). Code that needs stage-specific behavior should check
2963		this.
2964
2965- CONFIG_TPL_BUILD
2966		Set when the currently-running compilation is for an artifact
2967		that will end up in the TPL (as opposed to the SPL or U-Boot
2968		proper). Code that needs stage-specific behavior should check
2969		this.
2970
2971- CONFIG_SYS_MPC85XX_NO_RESETVEC
2972		Only for 85xx systems. If this variable is specified, the section
2973		.resetvec is not kept and the section .bootpg is placed in the
2974		previous 4k of the .text section.
2975
2976- CONFIG_ARCH_MAP_SYSMEM
2977		Generally U-Boot (and in particular the md command) uses
2978		effective address. It is therefore not necessary to regard
2979		U-Boot address as virtual addresses that need to be translated
2980		to physical addresses. However, sandbox requires this, since
2981		it maintains its own little RAM buffer which contains all
2982		addressable memory. This option causes some memory accesses
2983		to be mapped through map_sysmem() / unmap_sysmem().
2984
2985- CONFIG_X86_RESET_VECTOR
2986		If defined, the x86 reset vector code is included. This is not
2987		needed when U-Boot is running from Coreboot.
2988
2989- CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
2990		Option to disable subpage write in NAND driver
2991		driver that uses this:
2992		drivers/mtd/nand/raw/davinci_nand.c
2993
2994Freescale QE/FMAN Firmware Support:
2995-----------------------------------
2996
2997The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
2998loading of "firmware", which is encoded in the QE firmware binary format.
2999This firmware often needs to be loaded during U-Boot booting, so macros
3000are used to identify the storage device (NOR flash, SPI, etc) and the address
3001within that device.
3002
3003- CONFIG_SYS_FMAN_FW_ADDR
3004	The address in the storage device where the FMAN microcode is located.  The
3005	meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
3006	is also specified.
3007
3008- CONFIG_SYS_QE_FW_ADDR
3009	The address in the storage device where the QE microcode is located.  The
3010	meaning of this address depends on which CONFIG_SYS_QE_FMAN_FW_IN_xxx macro
3011	is also specified.
3012
3013- CONFIG_SYS_QE_FMAN_FW_LENGTH
3014	The maximum possible size of the firmware.  The firmware binary format
3015	has a field that specifies the actual size of the firmware, but it
3016	might not be possible to read any part of the firmware unless some
3017	local storage is allocated to hold the entire firmware first.
3018
3019- CONFIG_SYS_QE_FMAN_FW_IN_NOR
3020	Specifies that QE/FMAN firmware is located in NOR flash, mapped as
3021	normal addressable memory via the LBC.  CONFIG_SYS_FMAN_FW_ADDR is the
3022	virtual address in NOR flash.
3023
3024- CONFIG_SYS_QE_FMAN_FW_IN_NAND
3025	Specifies that QE/FMAN firmware is located in NAND flash.
3026	CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
3027
3028- CONFIG_SYS_QE_FMAN_FW_IN_MMC
3029	Specifies that QE/FMAN firmware is located on the primary SD/MMC
3030	device.  CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
3031
3032- CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
3033	Specifies that QE/FMAN firmware is located in the remote (master)
3034	memory space.	CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
3035	can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
3036	window->master inbound window->master LAW->the ucode address in
3037	master's memory space.
3038
3039Freescale Layerscape Management Complex Firmware Support:
3040---------------------------------------------------------
3041The Freescale Layerscape Management Complex (MC) supports the loading of
3042"firmware".
3043This firmware often needs to be loaded during U-Boot booting, so macros
3044are used to identify the storage device (NOR flash, SPI, etc) and the address
3045within that device.
3046
3047- CONFIG_FSL_MC_ENET
3048	Enable the MC driver for Layerscape SoCs.
3049
3050Freescale Layerscape Debug Server Support:
3051-------------------------------------------
3052The Freescale Layerscape Debug Server Support supports the loading of
3053"Debug Server firmware" and triggering SP boot-rom.
3054This firmware often needs to be loaded during U-Boot booting.
3055
3056- CONFIG_SYS_MC_RSV_MEM_ALIGN
3057	Define alignment of reserved memory MC requires
3058
3059Reproducible builds
3060-------------------
3061
3062In order to achieve reproducible builds, timestamps used in the U-Boot build
3063process have to be set to a fixed value.
3064
3065This is done using the SOURCE_DATE_EPOCH environment variable.
3066SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
3067option for U-Boot or an environment variable in U-Boot.
3068
3069SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
3070
3071Building the Software:
3072======================
3073
3074Building U-Boot has been tested in several native build environments
3075and in many different cross environments. Of course we cannot support
3076all possibly existing versions of cross development tools in all
3077(potentially obsolete) versions. In case of tool chain problems we
3078recommend to use the ELDK (see http://www.denx.de/wiki/DULG/ELDK)
3079which is extensively used to build and test U-Boot.
3080
3081If you are not using a native environment, it is assumed that you
3082have GNU cross compiling tools available in your path. In this case,
3083you must set the environment variable CROSS_COMPILE in your shell.
3084Note that no changes to the Makefile or any other source files are
3085necessary. For example using the ELDK on a 4xx CPU, please enter:
3086
3087	$ CROSS_COMPILE=ppc_4xx-
3088	$ export CROSS_COMPILE
3089
3090U-Boot is intended to be simple to build. After installing the
3091sources you must configure U-Boot for one specific board type. This
3092is done by typing:
3093
3094	make NAME_defconfig
3095
3096where "NAME_defconfig" is the name of one of the existing configu-
3097rations; see configs/*_defconfig for supported names.
3098
3099Note: for some boards special configuration names may exist; check if
3100      additional information is available from the board vendor; for
3101      instance, the TQM823L systems are available without (standard)
3102      or with LCD support. You can select such additional "features"
3103      when choosing the configuration, i. e.
3104
3105      make TQM823L_defconfig
3106	- will configure for a plain TQM823L, i. e. no LCD support
3107
3108      make TQM823L_LCD_defconfig
3109	- will configure for a TQM823L with U-Boot console on LCD
3110
3111      etc.
3112
3113
3114Finally, type "make all", and you should get some working U-Boot
3115images ready for download to / installation on your system:
3116
3117- "u-boot.bin" is a raw binary image
3118- "u-boot" is an image in ELF binary format
3119- "u-boot.srec" is in Motorola S-Record format
3120
3121By default the build is performed locally and the objects are saved
3122in the source directory. One of the two methods can be used to change
3123this behavior and build U-Boot to some external directory:
3124
31251. Add O= to the make command line invocations:
3126
3127	make O=/tmp/build distclean
3128	make O=/tmp/build NAME_defconfig
3129	make O=/tmp/build all
3130
31312. Set environment variable KBUILD_OUTPUT to point to the desired location:
3132
3133	export KBUILD_OUTPUT=/tmp/build
3134	make distclean
3135	make NAME_defconfig
3136	make all
3137
3138Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
3139variable.
3140
3141User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
3142setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
3143For example to treat all compiler warnings as errors:
3144
3145	make KCFLAGS=-Werror
3146
3147Please be aware that the Makefiles assume you are using GNU make, so
3148for instance on NetBSD you might need to use "gmake" instead of
3149native "make".
3150
3151
3152If the system board that you have is not listed, then you will need
3153to port U-Boot to your hardware platform. To do this, follow these
3154steps:
3155
31561.  Create a new directory to hold your board specific code. Add any
3157    files you need. In your board directory, you will need at least
3158    the "Makefile" and a "<board>.c".
31592.  Create a new configuration file "include/configs/<board>.h" for
3160    your board.
31613.  If you're porting U-Boot to a new CPU, then also create a new
3162    directory to hold your CPU specific code. Add any files you need.
31634.  Run "make <board>_defconfig" with your new name.
31645.  Type "make", and you should get a working "u-boot.srec" file
3165    to be installed on your target system.
31666.  Debug and solve any problems that might arise.
3167    [Of course, this last step is much harder than it sounds.]
3168
3169
3170Testing of U-Boot Modifications, Ports to New Hardware, etc.:
3171==============================================================
3172
3173If you have modified U-Boot sources (for instance added a new board
3174or support for new devices, a new CPU, etc.) you are expected to
3175provide feedback to the other developers. The feedback normally takes
3176the form of a "patch", i.e. a context diff against a certain (latest
3177official or latest in the git repository) version of U-Boot sources.
3178
3179But before you submit such a patch, please verify that your modifi-
3180cation did not break existing code. At least make sure that *ALL* of
3181the supported boards compile WITHOUT ANY compiler warnings. To do so,
3182just run the buildman script (tools/buildman/buildman), which will
3183configure and build U-Boot for ALL supported system. Be warned, this
3184will take a while. Please see the buildman README, or run 'buildman -H'
3185for documentation.
3186
3187
3188See also "U-Boot Porting Guide" below.
3189
3190
3191Monitor Commands - Overview:
3192============================
3193
3194go	- start application at address 'addr'
3195run	- run commands in an environment variable
3196bootm	- boot application image from memory
3197bootp	- boot image via network using BootP/TFTP protocol
3198bootz   - boot zImage from memory
3199tftpboot- boot image via network using TFTP protocol
3200	       and env variables "ipaddr" and "serverip"
3201	       (and eventually "gatewayip")
3202tftpput - upload a file via network using TFTP protocol
3203rarpboot- boot image via network using RARP/TFTP protocol
3204diskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'
3205loads	- load S-Record file over serial line
3206loadb	- load binary file over serial line (kermit mode)
3207md	- memory display
3208mm	- memory modify (auto-incrementing)
3209nm	- memory modify (constant address)
3210mw	- memory write (fill)
3211ms	- memory search
3212cp	- memory copy
3213cmp	- memory compare
3214crc32	- checksum calculation
3215i2c	- I2C sub-system
3216sspi	- SPI utility commands
3217base	- print or set address offset
3218printenv- print environment variables
3219setenv	- set environment variables
3220saveenv - save environment variables to persistent storage
3221protect - enable or disable FLASH write protection
3222erase	- erase FLASH memory
3223flinfo	- print FLASH memory information
3224nand	- NAND memory operations (see doc/README.nand)
3225bdinfo	- print Board Info structure
3226iminfo	- print header information for application image
3227coninfo - print console devices and informations
3228ide	- IDE sub-system
3229loop	- infinite loop on address range
3230loopw	- infinite write loop on address range
3231mtest	- simple RAM test
3232icache	- enable or disable instruction cache
3233dcache	- enable or disable data cache
3234reset	- Perform RESET of the CPU
3235echo	- echo args to console
3236version - print monitor version
3237help	- print online help
3238?	- alias for 'help'
3239
3240
3241Monitor Commands - Detailed Description:
3242========================================
3243
3244TODO.
3245
3246For now: just type "help <command>".
3247
3248
3249Environment Variables:
3250======================
3251
3252U-Boot supports user configuration using Environment Variables which
3253can be made persistent by saving to Flash memory.
3254
3255Environment Variables are set using "setenv", printed using
3256"printenv", and saved to Flash using "saveenv". Using "setenv"
3257without a value can be used to delete a variable from the
3258environment. As long as you don't save the environment you are
3259working with an in-memory copy. In case the Flash area containing the
3260environment is erased by accident, a default environment is provided.
3261
3262Some configuration options can be set using Environment Variables.
3263
3264List of environment variables (most likely not complete):
3265
3266  baudrate	- see CONFIG_BAUDRATE
3267
3268  bootdelay	- see CONFIG_BOOTDELAY
3269
3270  bootcmd	- see CONFIG_BOOTCOMMAND
3271
3272  bootargs	- Boot arguments when booting an RTOS image
3273
3274  bootfile	- Name of the image to load with TFTP
3275
3276  bootm_low	- Memory range available for image processing in the bootm
3277		  command can be restricted. This variable is given as
3278		  a hexadecimal number and defines lowest address allowed
3279		  for use by the bootm command. See also "bootm_size"
3280		  environment variable. Address defined by "bootm_low" is
3281		  also the base of the initial memory mapping for the Linux
3282		  kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and
3283		  bootm_mapsize.
3284
3285  bootm_mapsize - Size of the initial memory mapping for the Linux kernel.
3286		  This variable is given as a hexadecimal number and it
3287		  defines the size of the memory region starting at base
3288		  address bootm_low that is accessible by the Linux kernel
3289		  during early boot.  If unset, CONFIG_SYS_BOOTMAPSZ is used
3290		  as the default value if it is defined, and bootm_size is
3291		  used otherwise.
3292
3293  bootm_size	- Memory range available for image processing in the bootm
3294		  command can be restricted. This variable is given as
3295		  a hexadecimal number and defines the size of the region
3296		  allowed for use by the bootm command. See also "bootm_low"
3297		  environment variable.
3298
3299  bootstopkeysha256, bootdelaykey, bootstopkey	- See README.autoboot
3300
3301  updatefile	- Location of the software update file on a TFTP server, used
3302		  by the automatic software update feature. Please refer to
3303		  documentation in doc/README.update for more details.
3304
3305  autoload	- if set to "no" (any string beginning with 'n'),
3306		  "bootp" will just load perform a lookup of the
3307		  configuration from the BOOTP server, but not try to
3308		  load any image using TFTP
3309
3310  autostart	- if set to "yes", an image loaded using the "bootp",
3311		  "rarpboot", "tftpboot" or "diskboot" commands will
3312		  be automatically started (by internally calling
3313		  "bootm")
3314
3315		  If set to "no", a standalone image passed to the
3316		  "bootm" command will be copied to the load address
3317		  (and eventually uncompressed), but NOT be started.
3318		  This can be used to load and uncompress arbitrary
3319		  data.
3320
3321  fdt_high	- if set this restricts the maximum address that the
3322		  flattened device tree will be copied into upon boot.
3323		  For example, if you have a system with 1 GB memory
3324		  at physical address 0x10000000, while Linux kernel
3325		  only recognizes the first 704 MB as low memory, you
3326		  may need to set fdt_high as 0x3C000000 to have the
3327		  device tree blob be copied to the maximum address
3328		  of the 704 MB low memory, so that Linux kernel can
3329		  access it during the boot procedure.
3330
3331		  If this is set to the special value 0xFFFFFFFF then
3332		  the fdt will not be copied at all on boot.  For this
3333		  to work it must reside in writable memory, have
3334		  sufficient padding on the end of it for u-boot to
3335		  add the information it needs into it, and the memory
3336		  must be accessible by the kernel.
3337
3338  fdtcontroladdr- if set this is the address of the control flattened
3339		  device tree used by U-Boot when CONFIG_OF_CONTROL is
3340		  defined.
3341
3342  i2cfast	- (PPC405GP|PPC405EP only)
3343		  if set to 'y' configures Linux I2C driver for fast
3344		  mode (400kHZ). This environment variable is used in
3345		  initialization code. So, for changes to be effective
3346		  it must be saved and board must be reset.
3347
3348  initrd_high	- restrict positioning of initrd images:
3349		  If this variable is not set, initrd images will be
3350		  copied to the highest possible address in RAM; this
3351		  is usually what you want since it allows for
3352		  maximum initrd size. If for some reason you want to
3353		  make sure that the initrd image is loaded below the
3354		  CONFIG_SYS_BOOTMAPSZ limit, you can set this environment
3355		  variable to a value of "no" or "off" or "0".
3356		  Alternatively, you can set it to a maximum upper
3357		  address to use (U-Boot will still check that it
3358		  does not overwrite the U-Boot stack and data).
3359
3360		  For instance, when you have a system with 16 MB
3361		  RAM, and want to reserve 4 MB from use by Linux,
3362		  you can do this by adding "mem=12M" to the value of
3363		  the "bootargs" variable. However, now you must make
3364		  sure that the initrd image is placed in the first
3365		  12 MB as well - this can be done with
3366
3367		  setenv initrd_high 00c00000
3368
3369		  If you set initrd_high to 0xFFFFFFFF, this is an
3370		  indication to U-Boot that all addresses are legal
3371		  for the Linux kernel, including addresses in flash
3372		  memory. In this case U-Boot will NOT COPY the
3373		  ramdisk at all. This may be useful to reduce the
3374		  boot time on your system, but requires that this
3375		  feature is supported by your Linux kernel.
3376
3377  ipaddr	- IP address; needed for tftpboot command
3378
3379  loadaddr	- Default load address for commands like "bootp",
3380		  "rarpboot", "tftpboot", "loadb" or "diskboot"
3381
3382  loads_echo	- see CONFIG_LOADS_ECHO
3383
3384  serverip	- TFTP server IP address; needed for tftpboot command
3385
3386  bootretry	- see CONFIG_BOOT_RETRY_TIME
3387
3388  bootdelaykey	- see CONFIG_AUTOBOOT_DELAY_STR
3389
3390  bootstopkey	- see CONFIG_AUTOBOOT_STOP_STR
3391
3392  ethprime	- controls which interface is used first.
3393
3394  ethact	- controls which interface is currently active.
3395		  For example you can do the following
3396
3397		  => setenv ethact FEC
3398		  => ping 192.168.0.1 # traffic sent on FEC
3399		  => setenv ethact SCC
3400		  => ping 10.0.0.1 # traffic sent on SCC
3401
3402  ethrotate	- When set to "no" U-Boot does not go through all
3403		  available network interfaces.
3404		  It just stays at the currently selected interface.
3405
3406  netretry	- When set to "no" each network operation will
3407		  either succeed or fail without retrying.
3408		  When set to "once" the network operation will
3409		  fail when all the available network interfaces
3410		  are tried once without success.
3411		  Useful on scripts which control the retry operation
3412		  themselves.
3413
3414  npe_ucode	- set load address for the NPE microcode
3415
3416  silent_linux  - If set then Linux will be told to boot silently, by
3417		  changing the console to be empty. If "yes" it will be
3418		  made silent. If "no" it will not be made silent. If
3419		  unset, then it will be made silent if the U-Boot console
3420		  is silent.
3421
3422  tftpsrcp	- If this is set, the value is used for TFTP's
3423		  UDP source port.
3424
3425  tftpdstp	- If this is set, the value is used for TFTP's UDP
3426		  destination port instead of the Well Know Port 69.
3427
3428  tftpblocksize - Block size to use for TFTP transfers; if not set,
3429		  we use the TFTP server's default block size
3430
3431  tftptimeout	- Retransmission timeout for TFTP packets (in milli-
3432		  seconds, minimum value is 1000 = 1 second). Defines
3433		  when a packet is considered to be lost so it has to
3434		  be retransmitted. The default is 5000 = 5 seconds.
3435		  Lowering this value may make downloads succeed
3436		  faster in networks with high packet loss rates or
3437		  with unreliable TFTP servers.
3438
3439  tftptimeoutcountmax	- maximum count of TFTP timeouts (no
3440		  unit, minimum value = 0). Defines how many timeouts
3441		  can happen during a single file transfer before that
3442		  transfer is aborted. The default is 10, and 0 means
3443		  'no timeouts allowed'. Increasing this value may help
3444		  downloads succeed with high packet loss rates, or with
3445		  unreliable TFTP servers or client hardware.
3446
3447  tftpwindowsize	- if this is set, the value is used for TFTP's
3448		  window size as described by RFC 7440.
3449		  This means the count of blocks we can receive before
3450		  sending ack to server.
3451
3452  vlan		- When set to a value < 4095 the traffic over
3453		  Ethernet is encapsulated/received over 802.1q
3454		  VLAN tagged frames.
3455
3456  bootpretryperiod	- Period during which BOOTP/DHCP sends retries.
3457		  Unsigned value, in milliseconds. If not set, the period will
3458		  be either the default (28000), or a value based on
3459		  CONFIG_NET_RETRY_COUNT, if defined. This value has
3460		  precedence over the valu based on CONFIG_NET_RETRY_COUNT.
3461
3462  memmatches	- Number of matches found by the last 'ms' command, in hex
3463
3464  memaddr	- Address of the last match found by the 'ms' command, in hex,
3465		  or 0 if none
3466
3467  mempos	- Index position of the last match found by the 'ms' command,
3468		  in units of the size (.b, .w, .l) of the search
3469
3470
3471The following image location variables contain the location of images
3472used in booting. The "Image" column gives the role of the image and is
3473not an environment variable name. The other columns are environment
3474variable names. "File Name" gives the name of the file on a TFTP
3475server, "RAM Address" gives the location in RAM the image will be
3476loaded to, and "Flash Location" gives the image's address in NOR
3477flash or offset in NAND flash.
3478
3479*Note* - these variables don't have to be defined for all boards, some
3480boards currently use other variables for these purposes, and some
3481boards use these variables for other purposes.
3482
3483Image		    File Name	     RAM Address       Flash Location
3484-----		    ---------	     -----------       --------------
3485u-boot		    u-boot	     u-boot_addr_r     u-boot_addr
3486Linux kernel	    bootfile	     kernel_addr_r     kernel_addr
3487device tree blob    fdtfile	     fdt_addr_r	       fdt_addr
3488ramdisk		    ramdiskfile	     ramdisk_addr_r    ramdisk_addr
3489
3490The following environment variables may be used and automatically
3491updated by the network boot commands ("bootp" and "rarpboot"),
3492depending the information provided by your boot server:
3493
3494  bootfile	- see above
3495  dnsip		- IP address of your Domain Name Server
3496  dnsip2	- IP address of your secondary Domain Name Server
3497  gatewayip	- IP address of the Gateway (Router) to use
3498  hostname	- Target hostname
3499  ipaddr	- see above
3500  netmask	- Subnet Mask
3501  rootpath	- Pathname of the root filesystem on the NFS server
3502  serverip	- see above
3503
3504
3505There are two special Environment Variables:
3506
3507  serial#	- contains hardware identification information such
3508		  as type string and/or serial number
3509  ethaddr	- Ethernet address
3510
3511These variables can be set only once (usually during manufacturing of
3512the board). U-Boot refuses to delete or overwrite these variables
3513once they have been set once.
3514
3515
3516Further special Environment Variables:
3517
3518  ver		- Contains the U-Boot version string as printed
3519		  with the "version" command. This variable is
3520		  readonly (see CONFIG_VERSION_VARIABLE).
3521
3522
3523Please note that changes to some configuration parameters may take
3524only effect after the next boot (yes, that's just like Windoze :-).
3525
3526
3527Callback functions for environment variables:
3528---------------------------------------------
3529
3530For some environment variables, the behavior of u-boot needs to change
3531when their values are changed.  This functionality allows functions to
3532be associated with arbitrary variables.  On creation, overwrite, or
3533deletion, the callback will provide the opportunity for some side
3534effect to happen or for the change to be rejected.
3535
3536The callbacks are named and associated with a function using the
3537U_BOOT_ENV_CALLBACK macro in your board or driver code.
3538
3539These callbacks are associated with variables in one of two ways.  The
3540static list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATIC
3541in the board configuration to a string that defines a list of
3542associations.  The list must be in the following format:
3543
3544	entry = variable_name[:callback_name]
3545	list = entry[,list]
3546
3547If the callback name is not specified, then the callback is deleted.
3548Spaces are also allowed anywhere in the list.
3549
3550Callbacks can also be associated by defining the ".callbacks" variable
3551with the same list format above.  Any association in ".callbacks" will
3552override any association in the static list. You can define
3553CONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the
3554".callbacks" environment variable in the default or embedded environment.
3555
3556If CONFIG_REGEX is defined, the variable_name above is evaluated as a
3557regular expression. This allows multiple variables to be connected to
3558the same callback without explicitly listing them all out.
3559
3560The signature of the callback functions is:
3561
3562    int callback(const char *name, const char *value, enum env_op op, int flags)
3563
3564* name - changed environment variable
3565* value - new value of the environment variable
3566* op - operation (create, overwrite, or delete)
3567* flags - attributes of the environment variable change, see flags H_* in
3568  include/search.h
3569
3570The return value is 0 if the variable change is accepted and 1 otherwise.
3571
3572Command Line Parsing:
3573=====================
3574
3575There are two different command line parsers available with U-Boot:
3576the old "simple" one, and the much more powerful "hush" shell:
3577
3578Old, simple command line parser:
3579--------------------------------
3580
3581- supports environment variables (through setenv / saveenv commands)
3582- several commands on one line, separated by ';'
3583- variable substitution using "... ${name} ..." syntax
3584- special characters ('$', ';') can be escaped by prefixing with '\',
3585  for example:
3586	setenv bootcmd bootm \${address}
3587- You can also escape text by enclosing in single apostrophes, for example:
3588	setenv addip 'setenv bootargs $bootargs ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off'
3589
3590Hush shell:
3591-----------
3592
3593- similar to Bourne shell, with control structures like
3594  if...then...else...fi, for...do...done; while...do...done,
3595  until...do...done, ...
3596- supports environment ("global") variables (through setenv / saveenv
3597  commands) and local shell variables (through standard shell syntax
3598  "name=value"); only environment variables can be used with "run"
3599  command
3600
3601General rules:
3602--------------
3603
3604(1) If a command line (or an environment variable executed by a "run"
3605    command) contains several commands separated by semicolon, and
3606    one of these commands fails, then the remaining commands will be
3607    executed anyway.
3608
3609(2) If you execute several variables with one call to run (i. e.
3610    calling run with a list of variables as arguments), any failing
3611    command will cause "run" to terminate, i. e. the remaining
3612    variables are not executed.
3613
3614Note for Redundant Ethernet Interfaces:
3615=======================================
3616
3617Some boards come with redundant Ethernet interfaces; U-Boot supports
3618such configurations and is capable of automatic selection of a
3619"working" interface when needed. MAC assignment works as follows:
3620
3621Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
3622MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
3623"eth1addr" (=>eth1), "eth2addr", ...
3624
3625If the network interface stores some valid MAC address (for instance
3626in SROM), this is used as default address if there is NO correspon-
3627ding setting in the environment; if the corresponding environment
3628variable is set, this overrides the settings in the card; that means:
3629
3630o If the SROM has a valid MAC address, and there is no address in the
3631  environment, the SROM's address is used.
3632
3633o If there is no valid address in the SROM, and a definition in the
3634  environment exists, then the value from the environment variable is
3635  used.
3636
3637o If both the SROM and the environment contain a MAC address, and
3638  both addresses are the same, this MAC address is used.
3639
3640o If both the SROM and the environment contain a MAC address, and the
3641  addresses differ, the value from the environment is used and a
3642  warning is printed.
3643
3644o If neither SROM nor the environment contain a MAC address, an error
3645  is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
3646  a random, locally-assigned MAC is used.
3647
3648If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
3649will be programmed into hardware as part of the initialization process.	 This
3650may be skipped by setting the appropriate 'ethmacskip' environment variable.
3651The naming convention is as follows:
3652"ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
3653
3654Image Formats:
3655==============
3656
3657U-Boot is capable of booting (and performing other auxiliary operations on)
3658images in two formats:
3659
3660New uImage format (FIT)
3661-----------------------
3662
3663Flexible and powerful format based on Flattened Image Tree -- FIT (similar
3664to Flattened Device Tree). It allows the use of images with multiple
3665components (several kernels, ramdisks, etc.), with contents protected by
3666SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
3667
3668
3669Old uImage format
3670-----------------
3671
3672Old image format is based on binary files which can be basically anything,
3673preceded by a special header; see the definitions in include/image.h for
3674details; basically, the header defines the following image properties:
3675
3676* Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
3677  4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
3678  LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
3679  Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,
3680  INTEGRITY).
3681* Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
3682  IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
3683  Currently supported: ARM, Intel x86, MIPS, NDS32, Nios II, PowerPC).
3684* Compression Type (uncompressed, gzip, bzip2)
3685* Load Address
3686* Entry Point
3687* Image Name
3688* Image Timestamp
3689
3690The header is marked by a special Magic Number, and both the header
3691and the data portions of the image are secured against corruption by
3692CRC32 checksums.
3693
3694
3695Linux Support:
3696==============
3697
3698Although U-Boot should support any OS or standalone application
3699easily, the main focus has always been on Linux during the design of
3700U-Boot.
3701
3702U-Boot includes many features that so far have been part of some
3703special "boot loader" code within the Linux kernel. Also, any
3704"initrd" images to be used are no longer part of one big Linux image;
3705instead, kernel and "initrd" are separate images. This implementation
3706serves several purposes:
3707
3708- the same features can be used for other OS or standalone
3709  applications (for instance: using compressed images to reduce the
3710  Flash memory footprint)
3711
3712- it becomes much easier to port new Linux kernel versions because
3713  lots of low-level, hardware dependent stuff are done by U-Boot
3714
3715- the same Linux kernel image can now be used with different "initrd"
3716  images; of course this also means that different kernel images can
3717  be run with the same "initrd". This makes testing easier (you don't
3718  have to build a new "zImage.initrd" Linux image when you just
3719  change a file in your "initrd"). Also, a field-upgrade of the
3720  software is easier now.
3721
3722
3723Linux HOWTO:
3724============
3725
3726Porting Linux to U-Boot based systems:
3727---------------------------------------
3728
3729U-Boot cannot save you from doing all the necessary modifications to
3730configure the Linux device drivers for use with your target hardware
3731(no, we don't intend to provide a full virtual machine interface to
3732Linux :-).
3733
3734But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
3735
3736Just make sure your machine specific header file (for instance
3737include/asm-ppc/tqm8xx.h) includes the same definition of the Board
3738Information structure as we define in include/asm-<arch>/u-boot.h,
3739and make sure that your definition of IMAP_ADDR uses the same value
3740as your U-Boot configuration in CONFIG_SYS_IMMR.
3741
3742Note that U-Boot now has a driver model, a unified model for drivers.
3743If you are adding a new driver, plumb it into driver model. If there
3744is no uclass available, you are encouraged to create one. See
3745doc/driver-model.
3746
3747
3748Configuring the Linux kernel:
3749-----------------------------
3750
3751No specific requirements for U-Boot. Make sure you have some root
3752device (initial ramdisk, NFS) for your target system.
3753
3754
3755Building a Linux Image:
3756-----------------------
3757
3758With U-Boot, "normal" build targets like "zImage" or "bzImage" are
3759not used. If you use recent kernel source, a new build target
3760"uImage" will exist which automatically builds an image usable by
3761U-Boot. Most older kernels also have support for a "pImage" target,
3762which was introduced for our predecessor project PPCBoot and uses a
3763100% compatible format.
3764
3765Example:
3766
3767	make TQM850L_defconfig
3768	make oldconfig
3769	make dep
3770	make uImage
3771
3772The "uImage" build target uses a special tool (in 'tools/mkimage') to
3773encapsulate a compressed Linux kernel image with header	 information,
3774CRC32 checksum etc. for use with U-Boot. This is what we are doing:
3775
3776* build a standard "vmlinux" kernel image (in ELF binary format):
3777
3778* convert the kernel into a raw binary image:
3779
3780	${CROSS_COMPILE}-objcopy -O binary \
3781				 -R .note -R .comment \
3782				 -S vmlinux linux.bin
3783
3784* compress the binary image:
3785
3786	gzip -9 linux.bin
3787
3788* package compressed binary image for U-Boot:
3789
3790	mkimage -A ppc -O linux -T kernel -C gzip \
3791		-a 0 -e 0 -n "Linux Kernel Image" \
3792		-d linux.bin.gz uImage
3793
3794
3795The "mkimage" tool can also be used to create ramdisk images for use
3796with U-Boot, either separated from the Linux kernel image, or
3797combined into one file. "mkimage" encapsulates the images with a 64
3798byte header containing information about target architecture,
3799operating system, image type, compression method, entry points, time
3800stamp, CRC32 checksums, etc.
3801
3802"mkimage" can be called in two ways: to verify existing images and
3803print the header information, or to build new images.
3804
3805In the first form (with "-l" option) mkimage lists the information
3806contained in the header of an existing U-Boot image; this includes
3807checksum verification:
3808
3809	tools/mkimage -l image
3810	  -l ==> list image header information
3811
3812The second form (with "-d" option) is used to build a U-Boot image
3813from a "data file" which is used as image payload:
3814
3815	tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
3816		      -n name -d data_file image
3817	  -A ==> set architecture to 'arch'
3818	  -O ==> set operating system to 'os'
3819	  -T ==> set image type to 'type'
3820	  -C ==> set compression type 'comp'
3821	  -a ==> set load address to 'addr' (hex)
3822	  -e ==> set entry point to 'ep' (hex)
3823	  -n ==> set image name to 'name'
3824	  -d ==> use image data from 'datafile'
3825
3826Right now, all Linux kernels for PowerPC systems use the same load
3827address (0x00000000), but the entry point address depends on the
3828kernel version:
3829
3830- 2.2.x kernels have the entry point at 0x0000000C,
3831- 2.3.x and later kernels have the entry point at 0x00000000.
3832
3833So a typical call to build a U-Boot image would read:
3834
3835	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
3836	> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
3837	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
3838	> examples/uImage.TQM850L
3839	Image Name:   2.4.4 kernel for TQM850L
3840	Created:      Wed Jul 19 02:34:59 2000
3841	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
3842	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
3843	Load Address: 0x00000000
3844	Entry Point:  0x00000000
3845
3846To verify the contents of the image (or check for corruption):
3847
3848	-> tools/mkimage -l examples/uImage.TQM850L
3849	Image Name:   2.4.4 kernel for TQM850L
3850	Created:      Wed Jul 19 02:34:59 2000
3851	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
3852	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
3853	Load Address: 0x00000000
3854	Entry Point:  0x00000000
3855
3856NOTE: for embedded systems where boot time is critical you can trade
3857speed for memory and install an UNCOMPRESSED image instead: this
3858needs more space in Flash, but boots much faster since it does not
3859need to be uncompressed:
3860
3861	-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
3862	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
3863	> -A ppc -O linux -T kernel -C none -a 0 -e 0 \
3864	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
3865	> examples/uImage.TQM850L-uncompressed
3866	Image Name:   2.4.4 kernel for TQM850L
3867	Created:      Wed Jul 19 02:34:59 2000
3868	Image Type:   PowerPC Linux Kernel Image (uncompressed)
3869	Data Size:    792160 Bytes = 773.59 kB = 0.76 MB
3870	Load Address: 0x00000000
3871	Entry Point:  0x00000000
3872
3873
3874Similar you can build U-Boot images from a 'ramdisk.image.gz' file
3875when your kernel is intended to use an initial ramdisk:
3876
3877	-> tools/mkimage -n 'Simple Ramdisk Image' \
3878	> -A ppc -O linux -T ramdisk -C gzip \
3879	> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
3880	Image Name:   Simple Ramdisk Image
3881	Created:      Wed Jan 12 14:01:50 2000
3882	Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
3883	Data Size:    566530 Bytes = 553.25 kB = 0.54 MB
3884	Load Address: 0x00000000
3885	Entry Point:  0x00000000
3886
3887The "dumpimage" is a tool to disassemble images built by mkimage. Its "-i"
3888option performs the converse operation of the mkimage's second form (the "-d"
3889option). Given an image built by mkimage, the dumpimage extracts a "data file"
3890from the image:
3891
3892	tools/dumpimage -i image -T type -p position data_file
3893	  -i ==> extract from the 'image' a specific 'data_file'
3894	  -T ==> set image type to 'type'
3895	  -p ==> 'position' (starting at 0) of the 'data_file' inside the 'image'
3896
3897
3898Installing a Linux Image:
3899-------------------------
3900
3901To downloading a U-Boot image over the serial (console) interface,
3902you must convert the image to S-Record format:
3903
3904	objcopy -I binary -O srec examples/image examples/image.srec
3905
3906The 'objcopy' does not understand the information in the U-Boot
3907image header, so the resulting S-Record file will be relative to
3908address 0x00000000. To load it to a given address, you need to
3909specify the target address as 'offset' parameter with the 'loads'
3910command.
3911
3912Example: install the image to address 0x40100000 (which on the
3913TQM8xxL is in the first Flash bank):
3914
3915	=> erase 40100000 401FFFFF
3916
3917	.......... done
3918	Erased 8 sectors
3919
3920	=> loads 40100000
3921	## Ready for S-Record download ...
3922	~>examples/image.srec
3923	1 2 3 4 5 6 7 8 9 10 11 12 13 ...
3924	...
3925	15989 15990 15991 15992
3926	[file transfer complete]
3927	[connected]
3928	## Start Addr = 0x00000000
3929
3930
3931You can check the success of the download using the 'iminfo' command;
3932this includes a checksum verification so you can be sure no data
3933corruption happened:
3934
3935	=> imi 40100000
3936
3937	## Checking Image at 40100000 ...
3938	   Image Name:	 2.2.13 for initrd on TQM850L
3939	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
3940	   Data Size:	 335725 Bytes = 327 kB = 0 MB
3941	   Load Address: 00000000
3942	   Entry Point:	 0000000c
3943	   Verifying Checksum ... OK
3944
3945
3946Boot Linux:
3947-----------
3948
3949The "bootm" command is used to boot an application that is stored in
3950memory (RAM or Flash). In case of a Linux kernel image, the contents
3951of the "bootargs" environment variable is passed to the kernel as
3952parameters. You can check and modify this variable using the
3953"printenv" and "setenv" commands:
3954
3955
3956	=> printenv bootargs
3957	bootargs=root=/dev/ram
3958
3959	=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
3960
3961	=> printenv bootargs
3962	bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
3963
3964	=> bootm 40020000
3965	## Booting Linux kernel at 40020000 ...
3966	   Image Name:	 2.2.13 for NFS on TQM850L
3967	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
3968	   Data Size:	 381681 Bytes = 372 kB = 0 MB
3969	   Load Address: 00000000
3970	   Entry Point:	 0000000c
3971	   Verifying Checksum ... OK
3972	   Uncompressing Kernel Image ... OK
3973	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
3974	Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
3975	time_init: decrementer frequency = 187500000/60
3976	Calibrating delay loop... 49.77 BogoMIPS
3977	Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
3978	...
3979
3980If you want to boot a Linux kernel with initial RAM disk, you pass
3981the memory addresses of both the kernel and the initrd image (PPBCOOT
3982format!) to the "bootm" command:
3983
3984	=> imi 40100000 40200000
3985
3986	## Checking Image at 40100000 ...
3987	   Image Name:	 2.2.13 for initrd on TQM850L
3988	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
3989	   Data Size:	 335725 Bytes = 327 kB = 0 MB
3990	   Load Address: 00000000
3991	   Entry Point:	 0000000c
3992	   Verifying Checksum ... OK
3993
3994	## Checking Image at 40200000 ...
3995	   Image Name:	 Simple Ramdisk Image
3996	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
3997	   Data Size:	 566530 Bytes = 553 kB = 0 MB
3998	   Load Address: 00000000
3999	   Entry Point:	 00000000
4000	   Verifying Checksum ... OK
4001
4002	=> bootm 40100000 40200000
4003	## Booting Linux kernel at 40100000 ...
4004	   Image Name:	 2.2.13 for initrd on TQM850L
4005	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4006	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4007	   Load Address: 00000000
4008	   Entry Point:	 0000000c
4009	   Verifying Checksum ... OK
4010	   Uncompressing Kernel Image ... OK
4011	## Loading RAMDisk Image at 40200000 ...
4012	   Image Name:	 Simple Ramdisk Image
4013	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
4014	   Data Size:	 566530 Bytes = 553 kB = 0 MB
4015	   Load Address: 00000000
4016	   Entry Point:	 00000000
4017	   Verifying Checksum ... OK
4018	   Loading Ramdisk ... OK
4019	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000
4020	Boot arguments: root=/dev/ram
4021	time_init: decrementer frequency = 187500000/60
4022	Calibrating delay loop... 49.77 BogoMIPS
4023	...
4024	RAMDISK: Compressed image found at block 0
4025	VFS: Mounted root (ext2 filesystem).
4026
4027	bash#
4028
4029Boot Linux and pass a flat device tree:
4030-----------
4031
4032First, U-Boot must be compiled with the appropriate defines. See the section
4033titled "Linux Kernel Interface" above for a more in depth explanation. The
4034following is an example of how to start a kernel and pass an updated
4035flat device tree:
4036
4037=> print oftaddr
4038oftaddr=0x300000
4039=> print oft
4040oft=oftrees/mpc8540ads.dtb
4041=> tftp $oftaddr $oft
4042Speed: 1000, full duplex
4043Using TSEC0 device
4044TFTP from server 192.168.1.1; our IP address is 192.168.1.101
4045Filename 'oftrees/mpc8540ads.dtb'.
4046Load address: 0x300000
4047Loading: #
4048done
4049Bytes transferred = 4106 (100a hex)
4050=> tftp $loadaddr $bootfile
4051Speed: 1000, full duplex
4052Using TSEC0 device
4053TFTP from server 192.168.1.1; our IP address is 192.168.1.2
4054Filename 'uImage'.
4055Load address: 0x200000
4056Loading:############
4057done
4058Bytes transferred = 1029407 (fb51f hex)
4059=> print loadaddr
4060loadaddr=200000
4061=> print oftaddr
4062oftaddr=0x300000
4063=> bootm $loadaddr - $oftaddr
4064## Booting image at 00200000 ...
4065   Image Name:	 Linux-2.6.17-dirty
4066   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4067   Data Size:	 1029343 Bytes = 1005.2 kB
4068   Load Address: 00000000
4069   Entry Point:	 00000000
4070   Verifying Checksum ... OK
4071   Uncompressing Kernel Image ... OK
4072Booting using flat device tree at 0x300000
4073Using MPC85xx ADS machine description
4074Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
4075[snip]
4076
4077
4078More About U-Boot Image Types:
4079------------------------------
4080
4081U-Boot supports the following image types:
4082
4083   "Standalone Programs" are directly runnable in the environment
4084	provided by U-Boot; it is expected that (if they behave
4085	well) you can continue to work in U-Boot after return from
4086	the Standalone Program.
4087   "OS Kernel Images" are usually images of some Embedded OS which
4088	will take over control completely. Usually these programs
4089	will install their own set of exception handlers, device
4090	drivers, set up the MMU, etc. - this means, that you cannot
4091	expect to re-enter U-Boot except by resetting the CPU.
4092   "RAMDisk Images" are more or less just data blocks, and their
4093	parameters (address, size) are passed to an OS kernel that is
4094	being started.
4095   "Multi-File Images" contain several images, typically an OS
4096	(Linux) kernel image and one or more data images like
4097	RAMDisks. This construct is useful for instance when you want
4098	to boot over the network using BOOTP etc., where the boot
4099	server provides just a single image file, but you want to get
4100	for instance an OS kernel and a RAMDisk image.
4101
4102	"Multi-File Images" start with a list of image sizes, each
4103	image size (in bytes) specified by an "uint32_t" in network
4104	byte order. This list is terminated by an "(uint32_t)0".
4105	Immediately after the terminating 0 follow the images, one by
4106	one, all aligned on "uint32_t" boundaries (size rounded up to
4107	a multiple of 4 bytes).
4108
4109   "Firmware Images" are binary images containing firmware (like
4110	U-Boot or FPGA images) which usually will be programmed to
4111	flash memory.
4112
4113   "Script files" are command sequences that will be executed by
4114	U-Boot's command interpreter; this feature is especially
4115	useful when you configure U-Boot to use a real shell (hush)
4116	as command interpreter.
4117
4118Booting the Linux zImage:
4119-------------------------
4120
4121On some platforms, it's possible to boot Linux zImage. This is done
4122using the "bootz" command. The syntax of "bootz" command is the same
4123as the syntax of "bootm" command.
4124
4125Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
4126kernel with raw initrd images. The syntax is slightly different, the
4127address of the initrd must be augmented by it's size, in the following
4128format: "<initrd addres>:<initrd size>".
4129
4130
4131Standalone HOWTO:
4132=================
4133
4134One of the features of U-Boot is that you can dynamically load and
4135run "standalone" applications, which can use some resources of
4136U-Boot like console I/O functions or interrupt services.
4137
4138Two simple examples are included with the sources:
4139
4140"Hello World" Demo:
4141-------------------
4142
4143'examples/hello_world.c' contains a small "Hello World" Demo
4144application; it is automatically compiled when you build U-Boot.
4145It's configured to run at address 0x00040004, so you can play with it
4146like that:
4147
4148	=> loads
4149	## Ready for S-Record download ...
4150	~>examples/hello_world.srec
4151	1 2 3 4 5 6 7 8 9 10 11 ...
4152	[file transfer complete]
4153	[connected]
4154	## Start Addr = 0x00040004
4155
4156	=> go 40004 Hello World! This is a test.
4157	## Starting application at 0x00040004 ...
4158	Hello World
4159	argc = 7
4160	argv[0] = "40004"
4161	argv[1] = "Hello"
4162	argv[2] = "World!"
4163	argv[3] = "This"
4164	argv[4] = "is"
4165	argv[5] = "a"
4166	argv[6] = "test."
4167	argv[7] = "<NULL>"
4168	Hit any key to exit ...
4169
4170	## Application terminated, rc = 0x0
4171
4172Another example, which demonstrates how to register a CPM interrupt
4173handler with the U-Boot code, can be found in 'examples/timer.c'.
4174Here, a CPM timer is set up to generate an interrupt every second.
4175The interrupt service routine is trivial, just printing a '.'
4176character, but this is just a demo program. The application can be
4177controlled by the following keys:
4178
4179	? - print current values og the CPM Timer registers
4180	b - enable interrupts and start timer
4181	e - stop timer and disable interrupts
4182	q - quit application
4183
4184	=> loads
4185	## Ready for S-Record download ...
4186	~>examples/timer.srec
4187	1 2 3 4 5 6 7 8 9 10 11 ...
4188	[file transfer complete]
4189	[connected]
4190	## Start Addr = 0x00040004
4191
4192	=> go 40004
4193	## Starting application at 0x00040004 ...
4194	TIMERS=0xfff00980
4195	Using timer 1
4196	  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
4197
4198Hit 'b':
4199	[q, b, e, ?] Set interval 1000000 us
4200	Enabling timer
4201Hit '?':
4202	[q, b, e, ?] ........
4203	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
4204Hit '?':
4205	[q, b, e, ?] .
4206	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
4207Hit '?':
4208	[q, b, e, ?] .
4209	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
4210Hit '?':
4211	[q, b, e, ?] .
4212	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
4213Hit 'e':
4214	[q, b, e, ?] ...Stopping timer
4215Hit 'q':
4216	[q, b, e, ?] ## Application terminated, rc = 0x0
4217
4218
4219Minicom warning:
4220================
4221
4222Over time, many people have reported problems when trying to use the
4223"minicom" terminal emulation program for serial download. I (wd)
4224consider minicom to be broken, and recommend not to use it. Under
4225Unix, I recommend to use C-Kermit for general purpose use (and
4226especially for kermit binary protocol download ("loadb" command), and
4227use "cu" for S-Record download ("loads" command).  See
4228http://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
4229for help with kermit.
4230
4231
4232Nevertheless, if you absolutely want to use it try adding this
4233configuration to your "File transfer protocols" section:
4234
4235	   Name	   Program			Name U/D FullScr IO-Red. Multi
4236	X  kermit  /usr/bin/kermit -i -l %l -s	 Y    U	   Y	   N	  N
4237	Y  kermit  /usr/bin/kermit -i -l %l -r	 N    D	   Y	   N	  N
4238
4239
4240NetBSD Notes:
4241=============
4242
4243Starting at version 0.9.2, U-Boot supports NetBSD both as host
4244(build U-Boot) and target system (boots NetBSD/mpc8xx).
4245
4246Building requires a cross environment; it is known to work on
4247NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also
4248need gmake since the Makefiles are not compatible with BSD make).
4249Note that the cross-powerpc package does not install include files;
4250attempting to build U-Boot will fail because <machine/ansi.h> is
4251missing.  This file has to be installed and patched manually:
4252
4253	# cd /usr/pkg/cross/powerpc-netbsd/include
4254	# mkdir powerpc
4255	# ln -s powerpc machine
4256	# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h
4257	# ${EDIT} powerpc/ansi.h	## must remove __va_list, _BSD_VA_LIST
4258
4259Native builds *don't* work due to incompatibilities between native
4260and U-Boot include files.
4261
4262Booting assumes that (the first part of) the image booted is a
4263stage-2 loader which in turn loads and then invokes the kernel
4264proper. Loader sources will eventually appear in the NetBSD source
4265tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the
4266meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz
4267
4268
4269Implementation Internals:
4270=========================
4271
4272The following is not intended to be a complete description of every
4273implementation detail. However, it should help to understand the
4274inner workings of U-Boot and make it easier to port it to custom
4275hardware.
4276
4277
4278Initial Stack, Global Data:
4279---------------------------
4280
4281The implementation of U-Boot is complicated by the fact that U-Boot
4282starts running out of ROM (flash memory), usually without access to
4283system RAM (because the memory controller is not initialized yet).
4284This means that we don't have writable Data or BSS segments, and BSS
4285is not initialized as zero. To be able to get a C environment working
4286at all, we have to allocate at least a minimal stack. Implementation
4287options for this are defined and restricted by the CPU used: Some CPU
4288models provide on-chip memory (like the IMMR area on MPC8xx and
4289MPC826x processors), on others (parts of) the data cache can be
4290locked as (mis-) used as memory, etc.
4291
4292	Chris Hallinan posted a good summary of these issues to the
4293	U-Boot mailing list:
4294
4295	Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
4296	From: "Chris Hallinan" <clh@net1plus.com>
4297	Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
4298	...
4299
4300	Correct me if I'm wrong, folks, but the way I understand it
4301	is this: Using DCACHE as initial RAM for Stack, etc, does not
4302	require any physical RAM backing up the cache. The cleverness
4303	is that the cache is being used as a temporary supply of
4304	necessary storage before the SDRAM controller is setup. It's
4305	beyond the scope of this list to explain the details, but you
4306	can see how this works by studying the cache architecture and
4307	operation in the architecture and processor-specific manuals.
4308
4309	OCM is On Chip Memory, which I believe the 405GP has 4K. It
4310	is another option for the system designer to use as an
4311	initial stack/RAM area prior to SDRAM being available. Either
4312	option should work for you. Using CS 4 should be fine if your
4313	board designers haven't used it for something that would
4314	cause you grief during the initial boot! It is frequently not
4315	used.
4316
4317	CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
4318	with your processor/board/system design. The default value
4319	you will find in any recent u-boot distribution in
4320	walnut.h should work for you. I'd set it to a value larger
4321	than your SDRAM module. If you have a 64MB SDRAM module, set
4322	it above 400_0000. Just make sure your board has no resources
4323	that are supposed to respond to that address! That code in
4324	start.S has been around a while and should work as is when
4325	you get the config right.
4326
4327	-Chris Hallinan
4328	DS4.COM, Inc.
4329
4330It is essential to remember this, since it has some impact on the C
4331code for the initialization procedures:
4332
4333* Initialized global data (data segment) is read-only. Do not attempt
4334  to write it.
4335
4336* Do not use any uninitialized global data (or implicitly initialized
4337  as zero data - BSS segment) at all - this is undefined, initiali-
4338  zation is performed later (when relocating to RAM).
4339
4340* Stack space is very limited. Avoid big data buffers or things like
4341  that.
4342
4343Having only the stack as writable memory limits means we cannot use
4344normal global data to share information between the code. But it
4345turned out that the implementation of U-Boot can be greatly
4346simplified by making a global data structure (gd_t) available to all
4347functions. We could pass a pointer to this data as argument to _all_
4348functions, but this would bloat the code. Instead we use a feature of
4349the GCC compiler (Global Register Variables) to share the data: we
4350place a pointer (gd) to the global data into a register which we
4351reserve for this purpose.
4352
4353When choosing a register for such a purpose we are restricted by the
4354relevant  (E)ABI  specifications for the current architecture, and by
4355GCC's implementation.
4356
4357For PowerPC, the following registers have specific use:
4358	R1:	stack pointer
4359	R2:	reserved for system use
4360	R3-R4:	parameter passing and return values
4361	R5-R10: parameter passing
4362	R13:	small data area pointer
4363	R30:	GOT pointer
4364	R31:	frame pointer
4365
4366	(U-Boot also uses R12 as internal GOT pointer. r12
4367	is a volatile register so r12 needs to be reset when
4368	going back and forth between asm and C)
4369
4370    ==> U-Boot will use R2 to hold a pointer to the global data
4371
4372    Note: on PPC, we could use a static initializer (since the
4373    address of the global data structure is known at compile time),
4374    but it turned out that reserving a register results in somewhat
4375    smaller code - although the code savings are not that big (on
4376    average for all boards 752 bytes for the whole U-Boot image,
4377    624 text + 127 data).
4378
4379On ARM, the following registers are used:
4380
4381	R0:	function argument word/integer result
4382	R1-R3:	function argument word
4383	R9:	platform specific
4384	R10:	stack limit (used only if stack checking is enabled)
4385	R11:	argument (frame) pointer
4386	R12:	temporary workspace
4387	R13:	stack pointer
4388	R14:	link register
4389	R15:	program counter
4390
4391    ==> U-Boot will use R9 to hold a pointer to the global data
4392
4393    Note: on ARM, only R_ARM_RELATIVE relocations are supported.
4394
4395On Nios II, the ABI is documented here:
4396	http://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
4397
4398    ==> U-Boot will use gp to hold a pointer to the global data
4399
4400    Note: on Nios II, we give "-G0" option to gcc and don't use gp
4401    to access small data sections, so gp is free.
4402
4403On NDS32, the following registers are used:
4404
4405	R0-R1:	argument/return
4406	R2-R5:	argument
4407	R15:	temporary register for assembler
4408	R16:	trampoline register
4409	R28:	frame pointer (FP)
4410	R29:	global pointer (GP)
4411	R30:	link register (LP)
4412	R31:	stack pointer (SP)
4413	PC:	program counter (PC)
4414
4415    ==> U-Boot will use R10 to hold a pointer to the global data
4416
4417NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
4418or current versions of GCC may "optimize" the code too much.
4419
4420On RISC-V, the following registers are used:
4421
4422	x0: hard-wired zero (zero)
4423	x1: return address (ra)
4424	x2:	stack pointer (sp)
4425	x3:	global pointer (gp)
4426	x4:	thread pointer (tp)
4427	x5:	link register (t0)
4428	x8:	frame pointer (fp)
4429	x10-x11:	arguments/return values (a0-1)
4430	x12-x17:	arguments (a2-7)
4431	x28-31:	 temporaries (t3-6)
4432	pc:	program counter (pc)
4433
4434    ==> U-Boot will use gp to hold a pointer to the global data
4435
4436Memory Management:
4437------------------
4438
4439U-Boot runs in system state and uses physical addresses, i.e. the
4440MMU is not used either for address mapping nor for memory protection.
4441
4442The available memory is mapped to fixed addresses using the memory
4443controller. In this process, a contiguous block is formed for each
4444memory type (Flash, SDRAM, SRAM), even when it consists of several
4445physical memory banks.
4446
4447U-Boot is installed in the first 128 kB of the first Flash bank (on
4448TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
4449booting and sizing and initializing DRAM, the code relocates itself
4450to the upper end of DRAM. Immediately below the U-Boot code some
4451memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
4452configuration setting]. Below that, a structure with global Board
4453Info data is placed, followed by the stack (growing downward).
4454
4455Additionally, some exception handler code is copied to the low 8 kB
4456of DRAM (0x00000000 ... 0x00001FFF).
4457
4458So a typical memory configuration with 16 MB of DRAM could look like
4459this:
4460
4461	0x0000 0000	Exception Vector code
4462	      :
4463	0x0000 1FFF
4464	0x0000 2000	Free for Application Use
4465	      :
4466	      :
4467
4468	      :
4469	      :
4470	0x00FB FF20	Monitor Stack (Growing downward)
4471	0x00FB FFAC	Board Info Data and permanent copy of global data
4472	0x00FC 0000	Malloc Arena
4473	      :
4474	0x00FD FFFF
4475	0x00FE 0000	RAM Copy of Monitor Code
4476	...		eventually: LCD or video framebuffer
4477	...		eventually: pRAM (Protected RAM - unchanged by reset)
4478	0x00FF FFFF	[End of RAM]
4479
4480
4481System Initialization:
4482----------------------
4483
4484In the reset configuration, U-Boot starts at the reset entry point
4485(on most PowerPC systems at address 0x00000100). Because of the reset
4486configuration for CS0# this is a mirror of the on board Flash memory.
4487To be able to re-map memory U-Boot then jumps to its link address.
4488To be able to implement the initialization code in C, a (small!)
4489initial stack is set up in the internal Dual Ported RAM (in case CPUs
4490which provide such a feature like), or in a locked part of the data
4491cache. After that, U-Boot initializes the CPU core, the caches and
4492the SIU.
4493
4494Next, all (potentially) available memory banks are mapped using a
4495preliminary mapping. For example, we put them on 512 MB boundaries
4496(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
4497on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
4498programmed for SDRAM access. Using the temporary configuration, a
4499simple memory test is run that determines the size of the SDRAM
4500banks.
4501
4502When there is more than one SDRAM bank, and the banks are of
4503different size, the largest is mapped first. For equal size, the first
4504bank (CS2#) is mapped first. The first mapping is always for address
45050x00000000, with any additional banks following immediately to create
4506contiguous memory starting from 0.
4507
4508Then, the monitor installs itself at the upper end of the SDRAM area
4509and allocates memory for use by malloc() and for the global Board
4510Info data; also, the exception vector code is copied to the low RAM
4511pages, and the final stack is set up.
4512
4513Only after this relocation will you have a "normal" C environment;
4514until that you are restricted in several ways, mostly because you are
4515running from ROM, and because the code will have to be relocated to a
4516new address in RAM.
4517
4518
4519U-Boot Porting Guide:
4520----------------------
4521
4522[Based on messages by Jerry Van Baren in the U-Boot-Users mailing
4523list, October 2002]
4524
4525
4526int main(int argc, char *argv[])
4527{
4528	sighandler_t no_more_time;
4529
4530	signal(SIGALRM, no_more_time);
4531	alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
4532
4533	if (available_money > available_manpower) {
4534		Pay consultant to port U-Boot;
4535		return 0;
4536	}
4537
4538	Download latest U-Boot source;
4539
4540	Subscribe to u-boot mailing list;
4541
4542	if (clueless)
4543		email("Hi, I am new to U-Boot, how do I get started?");
4544
4545	while (learning) {
4546		Read the README file in the top level directory;
4547		Read http://www.denx.de/twiki/bin/view/DULG/Manual;
4548		Read applicable doc/README.*;
4549		Read the source, Luke;
4550		/* find . -name "*.[chS]" | xargs grep -i <keyword> */
4551	}
4552
4553	if (available_money > toLocalCurrency ($2500))
4554		Buy a BDI3000;
4555	else
4556		Add a lot of aggravation and time;
4557
4558	if (a similar board exists) {	/* hopefully... */
4559		cp -a board/<similar> board/<myboard>
4560		cp include/configs/<similar>.h include/configs/<myboard>.h
4561	} else {
4562		Create your own board support subdirectory;
4563		Create your own board include/configs/<myboard>.h file;
4564	}
4565	Edit new board/<myboard> files
4566	Edit new include/configs/<myboard>.h
4567
4568	while (!accepted) {
4569		while (!running) {
4570			do {
4571				Add / modify source code;
4572			} until (compiles);
4573			Debug;
4574			if (clueless)
4575				email("Hi, I am having problems...");
4576		}
4577		Send patch file to the U-Boot email list;
4578		if (reasonable critiques)
4579			Incorporate improvements from email list code review;
4580		else
4581			Defend code as written;
4582	}
4583
4584	return 0;
4585}
4586
4587void no_more_time (int sig)
4588{
4589      hire_a_guru();
4590}
4591
4592
4593Coding Standards:
4594-----------------
4595
4596All contributions to U-Boot should conform to the Linux kernel
4597coding style; see the kernel coding style guide at
4598https://www.kernel.org/doc/html/latest/process/coding-style.html, and the
4599script "scripts/Lindent" in your Linux kernel source directory.
4600
4601Source files originating from a different project (for example the
4602MTD subsystem) are generally exempt from these guidelines and are not
4603reformatted to ease subsequent migration to newer versions of those
4604sources.
4605
4606Please note that U-Boot is implemented in C (and to some small parts in
4607Assembler); no C++ is used, so please do not use C++ style comments (//)
4608in your code.
4609
4610Please also stick to the following formatting rules:
4611- remove any trailing white space
4612- use TAB characters for indentation and vertical alignment, not spaces
4613- make sure NOT to use DOS '\r\n' line feeds
4614- do not add more than 2 consecutive empty lines to source files
4615- do not add trailing empty lines to source files
4616
4617Submissions which do not conform to the standards may be returned
4618with a request to reformat the changes.
4619
4620
4621Submitting Patches:
4622-------------------
4623
4624Since the number of patches for U-Boot is growing, we need to
4625establish some rules. Submissions which do not conform to these rules
4626may be rejected, even when they contain important and valuable stuff.
4627
4628Please see http://www.denx.de/wiki/U-Boot/Patches for details.
4629
4630Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
4631see https://lists.denx.de/listinfo/u-boot
4632
4633When you send a patch, please include the following information with
4634it:
4635
4636* For bug fixes: a description of the bug and how your patch fixes
4637  this bug. Please try to include a way of demonstrating that the
4638  patch actually fixes something.
4639
4640* For new features: a description of the feature and your
4641  implementation.
4642
4643* For major contributions, add a MAINTAINERS file with your
4644  information and associated file and directory references.
4645
4646* When you add support for a new board, don't forget to add a
4647  maintainer e-mail address to the boards.cfg file, too.
4648
4649* If your patch adds new configuration options, don't forget to
4650  document these in the README file.
4651
4652* The patch itself. If you are using git (which is *strongly*
4653  recommended) you can easily generate the patch using the
4654  "git format-patch". If you then use "git send-email" to send it to
4655  the U-Boot mailing list, you will avoid most of the common problems
4656  with some other mail clients.
4657
4658  If you cannot use git, use "diff -purN OLD NEW". If your version of
4659  diff does not support these options, then get the latest version of
4660  GNU diff.
4661
4662  The current directory when running this command shall be the parent
4663  directory of the U-Boot source tree (i. e. please make sure that
4664  your patch includes sufficient directory information for the
4665  affected files).
4666
4667  We prefer patches as plain text. MIME attachments are discouraged,
4668  and compressed attachments must not be used.
4669
4670* If one logical set of modifications affects or creates several
4671  files, all these changes shall be submitted in a SINGLE patch file.
4672
4673* Changesets that contain different, unrelated modifications shall be
4674  submitted as SEPARATE patches, one patch per changeset.
4675
4676
4677Notes:
4678
4679* Before sending the patch, run the buildman script on your patched
4680  source tree and make sure that no errors or warnings are reported
4681  for any of the boards.
4682
4683* Keep your modifications to the necessary minimum: A patch
4684  containing several unrelated changes or arbitrary reformats will be
4685  returned with a request to re-formatting / split it.
4686
4687* If you modify existing code, make sure that your new code does not
4688  add to the memory footprint of the code ;-) Small is beautiful!
4689  When adding new features, these should compile conditionally only
4690  (using #ifdef), and the resulting code with the new feature
4691  disabled must not need more memory than the old code without your
4692  modification.
4693
4694* Remember that there is a size limit of 100 kB per message on the
4695  u-boot mailing list. Bigger patches will be moderated. If they are
4696  reasonable and not too big, they will be acknowledged. But patches
4697  bigger than the size limit should be avoided.
4698