1/*
2 * Copyright (c) 1998 Robert Nordier
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are freely
6 * permitted provided that the above copyright notice and this
7 * paragraph and the following disclaimer are duplicated in all
8 * such forms.
9 *
10 * This software is provided "AS IS" and without any express or
11 * implied warranties, including, without limitation, the implied
12 * warranties of merchantability and fitness for a particular
13 * purpose.
14 *
15 * $FreeBSD$
16 */
17
18/* A 1024-byte boot manager. */
19
20		.set NHRDRV,0x475		# Number of hard drives
21		.set ORIGIN,0x600		# Execution address
22		.set SECTOR_SIZE,0x200		# Length of a sector
23		.set NUM_SECTORS,2		# Total length in sectors
24
25		.set FAKE,ORIGIN+(SECTOR_SIZE*NUM_SECTORS) # Partition entry
26		.set LOAD,0x7c00		# Load address
27
28		.set PRT_OFF,0x1be		# Partition table
29
30		.set TBL0SZ,table0_end-table0	# Table 0 size
31		.set TBL1SZ,table1_end-table1	# Table 1 size
32
33		.set MAGIC,0xaa55		# Magic: bootable
34
35		.set KEY_ENTER,0x1c		# Enter key scan code
36		.set KEY_F1,0x3b		# F1 key scan code
37		.set KEY_1,0x02			# #1 key scan code
38
39/*
40 * Flag bits
41 */
42		.set FL_PACKET,0x80		# Packet mode
43		.set FL_NOUPDATE,0x40		# Don't save selection
44		.set FL_SETDRV,0x20		# Override drive number
45/*
46 * Addresses in the sector of embedded data values.
47 * Accessed with negative offsets from the end of the relocated sectors (%bp).
48 */
49		.set _PRT_END,(FAKE-(ORIGIN+SECTOR_SIZE*(NUM_SECTORS-1)))
50		.set _NXTDRV,-(_PRT_END+0x48)	# Next drive
51		.set _OPT,-(_PRT_END+0x47)	# Default option
52		.set _SETDRV,-(_PRT_END+0x46)	# Drive to force
53		.set _FLAGS,-(_PRT_END+0x45)	# Flags
54		.set _TICKS,-(_PRT_END+0x44)	# Timeout ticks
55		.set _FAKE,0x0			# Fake partition entry
56		.set _MNUOPT,0xc		# Menu options
57
58		.globl start			# Entry point
59		.code16				# This runs in real mode
60
61/*
62 * Initialise segments and registers to known values.
63 * segments start at 0.
64 * The stack is immediately below the address we were loaded to.
65 *
66 * Note that this section of code is used as the first signature check in
67 * boot0cfg(8).
68 */
69start:		cld				# String ops inc
70		xorw %ax,%ax			# Zero
71		movw %ax,%es			# Address
72		movw %ax,%ds			#  data
73		movw %ax,%ss			# Set up
74		movw $LOAD,%sp			#  stack
75/*
76 * End signature code
77 */
78
79/*
80 * Set address for variable space beyond code, and clear it.
81 * Notice that this is also used to point to the values embedded in the block,
82 * by using negative offsets.
83 */
84		movw $fake,%bp			# Address variables
85		movw %bp,%di			# %di used in stosw
86		movw $0x8,%cx			# Words to clear
87		rep				# Zero
88		stosw				#  them
89		incb -0xe(%di)			# Sector number 1
90/*
91 * Check what flags were loaded with us; specifically, use a predefined Drive.
92 * If what the bios gives us is bad, use the '0' in the block instead, as well.
93 */
94		testb $FL_SETDRV,LOAD+flags-start # Set number drive?
95		jnz boot.1			# Yes
96		testb %dl,%dl			# Drive number valid?
97		js boot.2			# Possibly (0x80 set)
98boot.1:		movb LOAD+setdrv-start,%dl	# Drive number to use
99boot.2:
100/*
101 * Reload all of boot0 (including the extra sectors) into memory at the
102 * relocation address.
103 */
104		push %dx			# Save drive number
105		movw $start,%bx			# Origin we were linked for
106		movw %bp,%si			# Fake PTE
107		movw $0x200+NUM_SECTORS,%ax	# Read in all
108		callw intx13			#  of boot0
109		pop %dx				# Restore
110/*
111 * Relocate to the new copy of the code.
112 */
113		jmp main+ORIGIN-LOAD		# To relocated code
114/*
115 * Whatever we decided to use, now store it into the fake
116 * partition entry that lives in the data space above us.
117 */
118main:		movb %dl,_FAKE(%bp)		# Save drive number
119		callw putn			# To new line
120		pushw %dx			# Save drive number
121/*
122 * Start out with a pointer to the 4th byte of the first table entry
123 * so that after 4 iterations it's beyond the end of the sector.
124 * and beyond a 256 byte boundary and has overflowed 8 bits (see next comment).
125 * (remember that the table starts 2 bytes earlier than you would expect
126 * as the bootable flag is after it in the block)
127 */
128		movw $(partbl+0x4),%bx		# Partition table (+4)
129		xorw %dx,%dx			# Item number
130/*
131 * Loop around on the partition table, printing values until we
132 * pass a 256 byte boundary. The end of loop test is at main.5.
133 */
134main.3:		movb %ch,-0x4(%bx)		# Zero active flag (ch == 0)
135		btw %dx,_FLAGS(%bp)		# Entry enabled?
136		jnc main.5			# No
137/*
138 * If any of the entries in the table are
139 * the same as the 'type' in the slice table entry,
140 * then this is an empty or non bootable partition. Skip it.
141 */
142		movb (%bx),%al			# Load type
143		movw $tables,%di		# Lookup tables
144		movb $TBL0SZ,%cl		# Number of entries
145		repne				# Exclude
146		scasb				#  partition?
147		je main.5			# Yes
148/*
149 * Now scan the table of known types
150 */
151		movb $TBL1SZ,%cl		# Number of entries
152		repne				# Known
153		scasb				#  type?
154		jne main.4			# No
155/*
156 * If it matches get the matching element in the
157 * next array.  If it doesn't, we are already
158 * pointing at its first element which points to a "?".
159 */
160		addw $TBL1SZ,%di		# Adjust
161main.4:		movb (%di),%cl			# Partition
162		addw %cx,%di			#  description
163		callw putx			# Display it
164main.5:		incw %dx			# Next item
165		addb $0x10,%bl			# Next entry
166		jnc main.3			# Till done
167/*
168 * Passed a 256 byte boundary..
169 * table is finished.
170 * Add one to the drive number and check it is valid,
171 */
172		popw %ax			# Drive number
173		subb $0x80-0x1,%al		# Does next
174		cmpb NHRDRV,%al			#  drive exist? (from BIOS?)
175		jb main.6			# Yes
176/*
177 * If not then if there is only one drive,
178 * Don't display drive as an option.
179 */
180		decw %ax			# Already drive 0?
181		jz main.7			# Yes
182/*
183 * If it was illegal or we cycled through them,
184 * then go back to drive 0.
185 */
186		xorb %al,%al			# Drive 0
187/*
188 * Whatever drive we selected, make it an ascii digit and save it back
189 * to the "next drive" location in the loaded block in case we
190 * want to save it for next time.
191 * This also is part of the printed drive string so add 0x80 to indicate
192 * end of string.
193 */
194main.6:		addb $'0'|0x80,%al		# Save next
195		movb %al,_NXTDRV(%bp)		#  drive number
196		movw $drive,%di			# Display
197		callw putx			#  item
198/*
199 * Now that we've printed the drive (if we needed to), display a prompt.
200 * Get ready for the input by noting the time.
201 */
202main.7:		movw $prompt,%si		# Display
203		callw putstr			#  prompt
204		movb _OPT(%bp),%dl		# Display
205		decw %si			#  default
206		callw putkey			#  key
207		xorb %ah,%ah			# BIOS: Get
208		int $0x1a			#  system time
209		movw %dx,%di			# Ticks when
210		addw _TICKS(%bp),%di	 	#  timeout
211/*
212 * Busy loop, looking for keystrokes but
213 * keeping one eye on the time.
214 */
215main.8:		movb $0x1,%ah			# BIOS: Check
216		int $0x16			#  for keypress
217		jnz main.11			# Have one
218		xorb %ah,%ah			# BIOS: Get
219		int $0x1a			#  system time
220		cmpw %di,%dx			# Timeout?
221		jb main.8			# No
222/*
223 * If timed out or defaulting, come here.
224 */
225main.9:		movb _OPT(%bp),%al		# Load default
226		jmp main.12			# Join common code
227/*
228 * User's last try was bad, beep in displeasure.
229 * Since nothing was printed, just continue on as if the user
230 * hadn't done anything. This gives the effect of the user getting a beep
231 * for all bad keystrokes but no action until either the timeout
232 * occurs or the user hits a good key.
233 */
234main.10:	movb $0x7,%al			# Signal
235		callw putchr			#  error
236/*
237 * Get the keystroke.
238 */
239main.11:	xorb %ah,%ah			# BIOS: Get
240		int $0x16			#  keypress
241		movb %ah,%al			# Scan code
242/*
243 * If it's CR act as if timed out.
244 */
245		cmpb $KEY_ENTER,%al		# Enter pressed?
246		je main.9			# Yes
247/*
248 * Otherwise check if legal
249 * If not ask again.
250 */
251		subb $KEY_F1,%al		# Less F1 scan code
252		cmpb $0x4,%al			# F1..F5?
253		jna main.12			# Yes
254		subb $(KEY_1 - KEY_F1),%al	# Less #1 scan code
255		cmpb $0x4,%al			# #1..#5?
256		ja main.10			# No
257/*
258 * We have a selection.
259 * but if it's a bad selection go back to complain.
260 * The bits in MNUOPT were set when the options were printed.
261 * Anything not printed is not an option.
262 */
263main.12:	cbtw				# Option
264		btw %ax,_MNUOPT(%bp)	 	#  enabled?
265		jnc main.10			# No
266/*
267 * Save the info in the original tables
268 * for rewriting to the disk.
269 */
270		movb %al,_OPT(%bp)		# Save option
271		movw $fake,%si			# Partition for write
272		movb (%si),%dl			# Drive number
273		movw %si,%bx			# Partition for read
274		cmpb $0x4,%al			# F5/#5 pressed?
275		pushf				# Save
276		je main.13			# Yes
277		shlb $0x4,%al			# Point to
278		addw $partbl,%ax		#  selected
279		xchgw %bx,%ax	 		#  partition
280		movb $0x80,(%bx)		# Flag active
281/*
282 * If not asked to do a write-back (flags 0x40) don't do one.
283 */
284main.13:	pushw %bx			# Save
285		testb $FL_NOUPDATE,_FLAGS(%bp)	# Skip update?
286		jnz main.14			# Yes
287		movw $start,%bx			# Data to write
288		movw $0x301,%ax			# Write 1 sector
289		callw intx13			#  to disk
290main.14:	popw %si			# Restore
291		popf				# Restore
292/*
293 * If going to next drive, replace drive with selected one.
294 * Remember to un-ascii it. Hey 0x80 is already set, cool!
295 */
296		jne main.15			# If not F5/#5
297		movb _NXTDRV(%bp),%dl		# Next drive
298		subb $'0',%dl			#  number
299/*
300 * load  selected bootsector to the LOAD location in RAM.
301 * If it fails to read or isn't marked bootable, treat it
302 * as a bad selection.
303 */
304main.15:	movw $LOAD,%bx			# Address for read
305		movw $0x201,%ax			# Read 1 sector
306		callw intx13			#  from disk
307		jc main.10			# If error
308		cmpw $MAGIC,0x1fe(%bx)		# Bootable?
309		jne main.10			# No
310		callw putn			# Leave some space
311		jmp *%bx			# Invoke bootstrap
312
313/*
314 * Display routines
315 */
316
317putkey:		movb $'F',%al			# Display
318		callw putchr			#  'F'
319		movb $'1',%al			# Prepare
320		addb %dl,%al			#  digit
321		jmp putstr.1			# Display the rest
322
323/*
324 * Display the option and note that it is a valid option.
325 * That last point is a bit tricky..
326 */
327putx:		btsw %dx,_MNUOPT(%bp)		# Enable menu option
328		movw $item,%si			# Display
329		callw putkey			#  key
330		movw %di,%si			# Display the rest
331
332puts:		callw putstr			# Display string
333
334putn:		movw $crlf,%si			# To next line
335
336putstr:		lodsb				# Get byte
337		testb $0x80,%al 		# End of string?
338		jnz putstr.2			# Yes
339putstr.1:	callw putchr			# Display char
340		jmp putstr			# Continue
341putstr.2:	andb $~0x80,%al 		# Clear MSB
342
343putchr:		pushw %bx			# Save
344		movw $0x7,%bx	 		# Page:attribute
345		movb $0xe,%ah			# BIOS: Display
346		int $0x10			#  character
347		popw %bx			# Restore
348		retw				# To caller
349
350/*
351 * One-sector disk I/O routine
352 *
353 * Calling conventions: (assumes %si -> partition table entry)
354 *
355 * 0x1(%si)	- byte - head
356 * 0x2(%si)	- word - cylinder/sector
357 * 0x8(%si)	- long - LBA to use if needed
358 * %ah		- byte - operation, 2 = read, 3 = write
359 * %al		- byte - sector count
360 * %dl		- byte - drive number
361 * %es:(%bx)	- void - buffer to use for transfer
362 *
363 * If the head == 0xff, and cylinder/sector == 0xffff, then try
364 * to use the EDD stuff with the LBA offset instead of CHS.  However,
365 * use CHS if at all possible.
366 */
367
368intx13:		movb 0x1(%si),%dh		# Load head
369		movw 0x2(%si),%cx		# Load cylinder:sector
370		pushw %si			# Save
371		movw %sp,%di			# Save
372		cmpb $0xff,%dh			# Might we need LBA?
373		jne intx13.2			# No, just use CHS
374		cmpw $0xffff,%cx		# Do we need LBA?
375		jne intx13.2			# No
376		testb $FL_PACKET,_FLAGS(%bp)	# Try the packet interface?
377		jz intx13.2			# No
378		pushw %cx			# Save
379		pushw %bx			# Save
380		movw $0x55aa,%bx		# Magic
381		pushw %ax			# Save
382		movb $0x41,%ah			# BIOS: EDD extensions
383		int $0x13			#  present?
384		popw %ax			# Restore
385		jc intx13.1			# Not present, use CHS
386		cmpw $0xaa55,%bx		# Magic?
387		jne intx13.1			# Not present, use CHS
388		testb $0x1,%cl			# Packet mode available?
389		jz intx13.1			# No, use CHS
390		orb $0x40,%ah			# Use disk packet
391intx13.1:	popw %bx			# Restore
392		popw %cx			# Restore
393		testb $0x40,%ah			# Using packet mode?
394		jz intx13.2			# No, so skip the rest
395		pushl $0x0			# Set the
396		pushl 0x8(%si)			# LBA address
397		pushw %es			# Set the transfer
398		pushw %bx			#  buffer address
399		push $0x0			# Punch a hole in the stack
400		push $0x10			# Packet size
401		movw %sp,%si			# Packet pointer
402		xchgb %al,0x2(%si)		# Set the block count in the
403						#  packet and zero %al,
404						#  turning verify off for writes
405intx13.2:	int $0x13			# BIOS: Disk I/O
406		movw %di,%sp			# Restore
407		popw %si			# Restore
408		retw				# To caller
409
410		.org PRT_OFF-0xe,0x90
411/*
412 * These values are sometimes changed before writing back to the drive
413 * Be especially careful that nxtdrv: must come after drive:, as it
414 * is part of the same string.
415 *
416 * Note that the 'drive' string variable is used as the second signature
417 * check in boot0cfg(8).
418 */
419version_minor:	.byte 0x1			# minor version
420version_major:	.byte 0x1			# major version
421drive:		.ascii "Drive "
422nxtdrv:		.byte 0x0			# Next drive number
423opt:		.byte 0x0			# Option
424setdrv:		.byte 0x80			# Drive to force
425flags:		.byte FLAGS			# Flags
426ticks:		.word TICKS			# Delay
427
428/*
429 * here is the 64 byte partition table that fdisk would fiddle with.
430 */
431partbl:		.fill 0x40,0x1,0x0		# Partition table
432		.word MAGIC			# Magic number
433
434/*
435 * start of sector two.. ugh
436 */
437		.org SECTOR_SIZE,0x90
438
439/* Menu strings */
440
441item:		.ascii "  ";	     .byte ' '|0x80
442prompt:		.ascii "\nDefault:"; .byte ' '|0x80
443crlf:		.ascii "\r";	     .byte '\n'|0x80
444
445/* Partition type tables */
446
447tables:
448/*
449 * These entries identify invalid or NON BOOT types and partitions.
450 */
451table0:		.byte 0x0, 0x5, 0xf
452table0_end:
453/*
454 * These values indicate bootable types we know the names of
455 */
456table1:		.byte 0x1, 0x4, 0x6, 0x7, 0xb, 0xc, 0xe, 0x42, 0x63, 0x83
457		.byte 0x9f, 0xa5, 0xa6, 0xa9
458table1_end:
459/*
460 * These are offsets that match the known names above and point to the strings
461 * that will be printed.
462 */
463		.byte os_misc-. 		# Unknown
464		.byte os_dos-.			# DOS
465		.byte os_dos-.			# DOS
466		.byte os_dos-.			# DOS
467		.byte os_nt-.			# NT/XP or OS/2
468		.byte os_windows-.		# Windows 32-bit FAT
469		.byte os_windows-.		# Windows 32-bit FAT ext int 13
470		.byte os_windows-.		# Windows
471		.byte os_windows-.		# Windows 2000 dyn ext
472		.byte os_unix-. 		# UNIX
473		.byte os_linux-.		# Linux
474		.byte os_bsdos-.		# BSD/OS
475		.byte os_freebsd-.		# FreeBSD
476		.byte os_openbsd-.		# OpenBSD
477		.byte os_netbsd-.		# NetBSD
478/*
479 * And here are the strings themselves. 0x80 or'd into a byte indicates
480 * the end of the string. (not so great for Russians but...)
481 */
482os_misc:	.ascii "Unknow";	.byte 'n'|0x80
483os_dos:		.ascii "DO";		.byte 'S'|0x80
484os_nt:		.ascii "Windows NT/X";	.byte 'P'|0x80
485os_windows:	.ascii "Window";	.byte 's'|0x80
486os_unix:	.ascii "UNI";		.byte 'X'|0x80
487os_linux:	.ascii "Linu";		.byte 'x'|0x80
488os_freebsd:	.ascii "FreeBS";	.byte 'D'|0x80
489os_openbsd:	.ascii "OpenBS";	.byte 'D'|0x80
490os_netbsd:	.ascii "NetBS";		.byte 'D'|0x80
491os_bsdos:	.ascii "BSD/O";		.byte 'S'|0x80
492
493/*
494 * Fake partition entry created at the end of the table used when loading
495 * boot0 at the very beginning and when loading an MBR from another disk when
496 * F5 is pressed.
497 */
498		.org SECTOR_SIZE*NUM_SECTORS, 0x0
499fake:
500