16 */
17
18/* Memory Locations */
19 .set MEM_REL,0x700 # Relocation address
20 .set MEM_ARG,0x900 # Arguments
21 .set MEM_ORG,0x7c00 # Origin
22 .set MEM_BUF,0x8c00 # Load area
23 .set MEM_BTX,0x9000 # BTX start
24 .set MEM_JMP,0x9010 # BTX entry point
25 .set MEM_USR,0xa000 # Client start
26 .set BDA_BOOT,0x472 # Boot howto flag
27
28/* Partition Constants */
29 .set PRT_OFF,0x1be # Partition offset
30 .set PRT_NUM,0x4 # Partitions
31 .set PRT_BSD,0xa5 # Partition type
32
33/* Flag Bits */
34 .set FL_PACKET,0x80 # Packet mode
35
36/* Misc. Constants */
37 .set SIZ_PAG,0x1000 # Page size
38 .set SIZ_SEC,0x200 # Sector size
39
40 .set NSECT,0x10
41 .globl start
42 .globl xread
43 .code16
44
45start: jmp main # Start recognizably
46
47/*
48 * This is the start of a standard BIOS Parameter Block (BPB). Most bootable
49 * FAT disks have this at the start of their MBR. While normal BIOS's will
50 * work fine without this section, IBM's El Torito emulation "fixes" up the
51 * BPB by writing into the memory copy of the MBR. Rather than have data
52 * written into our xread routine, we'll define a BPB to work around it.
53 * The data marked with (T) indicates a field required for a ThinkPad to
54 * recognize the disk and (W) indicates fields written from IBM BIOS code.
55 * The use of the BPB is based on what OpenBSD and NetBSD implemented in
56 * their boot code but the required fields were determined by trial and error.
57 *
58 * Note: If additional space is needed in boot1, one solution would be to
59 * move the "prompt" message data (below) to replace the OEM ID.
60 */
61 .org 0x03, 0x00
62oemid: .space 0x08, 0x00 # OEM ID
63
64 .org 0x0b, 0x00
65bpb: .word 512 # sector size (T)
66 .byte 0 # sectors/clustor
67 .word 0 # reserved sectors
68 .byte 0 # number of FATs
69 .word 0 # root entries
70 .word 0 # small sectors
71 .byte 0 # media type (W)
72 .word 0 # sectors/fat
73 .word 18 # sectors per track (T)
74 .word 2 # number of heads (T)
75 .long 0 # hidden sectors (W)
76 .long 0 # large sectors
77
78 .org 0x24, 0x00
79ebpb: .byte 0 # BIOS physical drive number (W)
80
81 .org 0x25,0x90
82/*
83 * Trampoline used by boot2 to call read to read data from the disk via
84 * the BIOS. Call with:
85 *
86 * %cx:%ax - long - LBA to read in
87 * %es:(%bx) - caddr_t - buffer to read data into
88 * %dl - byte - drive to read from
89 * %dh - byte - num sectors to read
90 */
91
92xread: push %ss # Address
93 pop %ds # data
94/*
95 * Setup an EDD disk packet and pass it to read
96 */
97xread.1: # Starting
98 pushl $0x0 # absolute
99 push %cx # block
100 push %ax # number
101 push %es # Address of
102 push %bx # transfer buffer
103 xor %ax,%ax # Number of
104 movb %dh,%al # blocks to
105 push %ax # transfer
106 push $0x10 # Size of packet
107 mov %sp,%bp # Packet pointer
108 callw read # Read from disk
109 lea 0x10(%bp),%sp # Clear stack
110 lret # To far caller
111/*
112 * Load the rest of boot2 and BTX up, copy the parts to the right locations,
113 * and start it all up.
114 */
115
116/*
117 * Setup the segment registers to flat addressing (segment 0) and setup the
118 * stack to end just below the start of our code.
119 */
120main: cld # String ops inc
121 xor %cx,%cx # Zero
122 mov %cx,%es # Address
123 mov %cx,%ds # data
124 mov %cx,%ss # Set up
125 mov $start,%sp # stack
126/*
127 * Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
128 * %cx == 0x100.
129 */
130 mov %sp,%si # Source
131 mov $MEM_REL,%di # Destination
132 incb %ch # Word count
133 rep # Copy
134 movsw # code
135/*
136 * If we are on a hard drive, then load the MBR and look for the first
137 * FreeBSD slice. We use the fake partition entry below that points to
138 * the MBR when we call nread. The first pass looks for the first active
139 * FreeBSD slice. The second pass looks for the first non-active FreeBSD
140 * slice if the first one fails.
141 */
142 mov $part4,%si # Partition
143 cmpb $0x80,%dl # Hard drive?
144 jb main.4 # No
145 movb $0x1,%dh # Block count
146 callw nread # Read MBR
147 mov $0x1,%cx # Two passes
148main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table
149 movb $0x1,%dh # Partition
150main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type?
151 jne main.3 # No
152 jcxz main.5 # If second pass
153 testb $0x80,(%si) # Active?
154 jnz main.5 # Yes
155main.3: add $0x10,%si # Next entry
156 incb %dh # Partition
157 cmpb $0x1+PRT_NUM,%dh # In table?
158 jb main.2 # Yes
159 dec %cx # Do two
160 jcxz main.1 # passes
161/*
162 * If we get here, we didn't find any FreeBSD slices at all, so print an
163 * error message and die.
164 */
165 mov $msg_part,%si # Message
166 jmp error # Error
167/*
168 * Floppies use partition 0 of drive 0.
169 */
170main.4: xor %dx,%dx # Partition:drive
171/*
172 * Ok, we have a slice and drive in %dx now, so use that to locate and load
173 * boot2. %si references the start of the slice we are looking for, so go
174 * ahead and load up the first 16 sectors (boot1 + boot2) from that. When
175 * we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus,
176 * boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00.
177 * The first part of boot2 is the disklabel, which is 0x200 bytes long.
178 * The second part is BTX, which is thus loaded into 0x9000, which is where
179 * it also runs from. The boot2.bin binary starts right after the end of
180 * BTX, so we have to figure out where the start of it is and then move the
181 * binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but
182 * when we use btxld to create boot2, we use an entry point of 0x2000. That
183 * entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000.
184 */
185main.5: mov %dx,MEM_ARG # Save args
186 movb $NSECT,%dh # Sector count
187 callw nread # Read disk
188 mov $MEM_BTX,%bx # BTX
189 mov 0xa(%bx),%si # Get BTX length and set
190 add %bx,%si # %si to start of boot2.bin
191 mov $MEM_USR+SIZ_PAG*2,%di # Client page 2
192 mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx # Byte
193 sub %si,%cx # count
194 rep # Relocate
195 movsb # client
196
197/*
198 * Enable A20 so we can access memory above 1 meg.
199 * Use the zero-valued %cx as a timeout for embedded hardware which do not
200 * have a keyboard controller.
201 */
202seta20: cli # Disable interrupts
203seta20.1: dec %cx # Timeout?
204 jz seta20.3 # Yes
205 inb $0x64,%al # Get status
206 testb $0x2,%al # Busy?
207 jnz seta20.1 # Yes
208 movb $0xd1,%al # Command: Write
209 outb %al,$0x64 # output port
210seta20.2: inb $0x64,%al # Get status
211 testb $0x2,%al # Busy?
212 jnz seta20.2 # Yes
213 movb $0xdf,%al # Enable
214 outb %al,$0x60 # A20
215seta20.3: sti # Enable interrupts
216
217 jmp start+MEM_JMP-MEM_ORG # Start BTX
218
219
220/*
221 * Trampoline used to call read from within boot1.
222 */
223nread: mov $MEM_BUF,%bx # Transfer buffer
224 mov 0x8(%si),%ax # Get
225 mov 0xa(%si),%cx # LBA
226 push %cs # Read from
227 callw xread.1 # disk
228 jnc return # If success, return
229 mov $msg_read,%si # Otherwise, set the error
230 # message and fall through to
231 # the error routine
232/*
233 * Print out the error message pointed to by %ds:(%si) followed
234 * by a prompt, wait for a keypress, and then reboot the machine.
235 */
236error: callw putstr # Display message
237 mov $prompt,%si # Display
238 callw putstr # prompt
239 xorb %ah,%ah # BIOS: Get
240 int $0x16 # keypress
241 movw $0x1234, BDA_BOOT # Do a warm boot
| 16 */
17
18/* Memory Locations */
19 .set MEM_REL,0x700 # Relocation address
20 .set MEM_ARG,0x900 # Arguments
21 .set MEM_ORG,0x7c00 # Origin
22 .set MEM_BUF,0x8c00 # Load area
23 .set MEM_BTX,0x9000 # BTX start
24 .set MEM_JMP,0x9010 # BTX entry point
25 .set MEM_USR,0xa000 # Client start
26 .set BDA_BOOT,0x472 # Boot howto flag
27
28/* Partition Constants */
29 .set PRT_OFF,0x1be # Partition offset
30 .set PRT_NUM,0x4 # Partitions
31 .set PRT_BSD,0xa5 # Partition type
32
33/* Flag Bits */
34 .set FL_PACKET,0x80 # Packet mode
35
36/* Misc. Constants */
37 .set SIZ_PAG,0x1000 # Page size
38 .set SIZ_SEC,0x200 # Sector size
39
40 .set NSECT,0x10
41 .globl start
42 .globl xread
43 .code16
44
45start: jmp main # Start recognizably
46
47/*
48 * This is the start of a standard BIOS Parameter Block (BPB). Most bootable
49 * FAT disks have this at the start of their MBR. While normal BIOS's will
50 * work fine without this section, IBM's El Torito emulation "fixes" up the
51 * BPB by writing into the memory copy of the MBR. Rather than have data
52 * written into our xread routine, we'll define a BPB to work around it.
53 * The data marked with (T) indicates a field required for a ThinkPad to
54 * recognize the disk and (W) indicates fields written from IBM BIOS code.
55 * The use of the BPB is based on what OpenBSD and NetBSD implemented in
56 * their boot code but the required fields were determined by trial and error.
57 *
58 * Note: If additional space is needed in boot1, one solution would be to
59 * move the "prompt" message data (below) to replace the OEM ID.
60 */
61 .org 0x03, 0x00
62oemid: .space 0x08, 0x00 # OEM ID
63
64 .org 0x0b, 0x00
65bpb: .word 512 # sector size (T)
66 .byte 0 # sectors/clustor
67 .word 0 # reserved sectors
68 .byte 0 # number of FATs
69 .word 0 # root entries
70 .word 0 # small sectors
71 .byte 0 # media type (W)
72 .word 0 # sectors/fat
73 .word 18 # sectors per track (T)
74 .word 2 # number of heads (T)
75 .long 0 # hidden sectors (W)
76 .long 0 # large sectors
77
78 .org 0x24, 0x00
79ebpb: .byte 0 # BIOS physical drive number (W)
80
81 .org 0x25,0x90
82/*
83 * Trampoline used by boot2 to call read to read data from the disk via
84 * the BIOS. Call with:
85 *
86 * %cx:%ax - long - LBA to read in
87 * %es:(%bx) - caddr_t - buffer to read data into
88 * %dl - byte - drive to read from
89 * %dh - byte - num sectors to read
90 */
91
92xread: push %ss # Address
93 pop %ds # data
94/*
95 * Setup an EDD disk packet and pass it to read
96 */
97xread.1: # Starting
98 pushl $0x0 # absolute
99 push %cx # block
100 push %ax # number
101 push %es # Address of
102 push %bx # transfer buffer
103 xor %ax,%ax # Number of
104 movb %dh,%al # blocks to
105 push %ax # transfer
106 push $0x10 # Size of packet
107 mov %sp,%bp # Packet pointer
108 callw read # Read from disk
109 lea 0x10(%bp),%sp # Clear stack
110 lret # To far caller
111/*
112 * Load the rest of boot2 and BTX up, copy the parts to the right locations,
113 * and start it all up.
114 */
115
116/*
117 * Setup the segment registers to flat addressing (segment 0) and setup the
118 * stack to end just below the start of our code.
119 */
120main: cld # String ops inc
121 xor %cx,%cx # Zero
122 mov %cx,%es # Address
123 mov %cx,%ds # data
124 mov %cx,%ss # Set up
125 mov $start,%sp # stack
126/*
127 * Relocate ourself to MEM_REL. Since %cx == 0, the inc %ch sets
128 * %cx == 0x100.
129 */
130 mov %sp,%si # Source
131 mov $MEM_REL,%di # Destination
132 incb %ch # Word count
133 rep # Copy
134 movsw # code
135/*
136 * If we are on a hard drive, then load the MBR and look for the first
137 * FreeBSD slice. We use the fake partition entry below that points to
138 * the MBR when we call nread. The first pass looks for the first active
139 * FreeBSD slice. The second pass looks for the first non-active FreeBSD
140 * slice if the first one fails.
141 */
142 mov $part4,%si # Partition
143 cmpb $0x80,%dl # Hard drive?
144 jb main.4 # No
145 movb $0x1,%dh # Block count
146 callw nread # Read MBR
147 mov $0x1,%cx # Two passes
148main.1: mov $MEM_BUF+PRT_OFF,%si # Partition table
149 movb $0x1,%dh # Partition
150main.2: cmpb $PRT_BSD,0x4(%si) # Our partition type?
151 jne main.3 # No
152 jcxz main.5 # If second pass
153 testb $0x80,(%si) # Active?
154 jnz main.5 # Yes
155main.3: add $0x10,%si # Next entry
156 incb %dh # Partition
157 cmpb $0x1+PRT_NUM,%dh # In table?
158 jb main.2 # Yes
159 dec %cx # Do two
160 jcxz main.1 # passes
161/*
162 * If we get here, we didn't find any FreeBSD slices at all, so print an
163 * error message and die.
164 */
165 mov $msg_part,%si # Message
166 jmp error # Error
167/*
168 * Floppies use partition 0 of drive 0.
169 */
170main.4: xor %dx,%dx # Partition:drive
171/*
172 * Ok, we have a slice and drive in %dx now, so use that to locate and load
173 * boot2. %si references the start of the slice we are looking for, so go
174 * ahead and load up the first 16 sectors (boot1 + boot2) from that. When
175 * we read it in, we conveniently use 0x8c00 as our transfer buffer. Thus,
176 * boot1 ends up at 0x8c00, and boot2 starts at 0x8c00 + 0x200 = 0x8e00.
177 * The first part of boot2 is the disklabel, which is 0x200 bytes long.
178 * The second part is BTX, which is thus loaded into 0x9000, which is where
179 * it also runs from. The boot2.bin binary starts right after the end of
180 * BTX, so we have to figure out where the start of it is and then move the
181 * binary to 0xc000. Normally, BTX clients start at MEM_USR, or 0xa000, but
182 * when we use btxld to create boot2, we use an entry point of 0x2000. That
183 * entry point is relative to MEM_USR; thus boot2.bin starts at 0xc000.
184 */
185main.5: mov %dx,MEM_ARG # Save args
186 movb $NSECT,%dh # Sector count
187 callw nread # Read disk
188 mov $MEM_BTX,%bx # BTX
189 mov 0xa(%bx),%si # Get BTX length and set
190 add %bx,%si # %si to start of boot2.bin
191 mov $MEM_USR+SIZ_PAG*2,%di # Client page 2
192 mov $MEM_BTX+(NSECT-1)*SIZ_SEC,%cx # Byte
193 sub %si,%cx # count
194 rep # Relocate
195 movsb # client
196
197/*
198 * Enable A20 so we can access memory above 1 meg.
199 * Use the zero-valued %cx as a timeout for embedded hardware which do not
200 * have a keyboard controller.
201 */
202seta20: cli # Disable interrupts
203seta20.1: dec %cx # Timeout?
204 jz seta20.3 # Yes
205 inb $0x64,%al # Get status
206 testb $0x2,%al # Busy?
207 jnz seta20.1 # Yes
208 movb $0xd1,%al # Command: Write
209 outb %al,$0x64 # output port
210seta20.2: inb $0x64,%al # Get status
211 testb $0x2,%al # Busy?
212 jnz seta20.2 # Yes
213 movb $0xdf,%al # Enable
214 outb %al,$0x60 # A20
215seta20.3: sti # Enable interrupts
216
217 jmp start+MEM_JMP-MEM_ORG # Start BTX
218
219
220/*
221 * Trampoline used to call read from within boot1.
222 */
223nread: mov $MEM_BUF,%bx # Transfer buffer
224 mov 0x8(%si),%ax # Get
225 mov 0xa(%si),%cx # LBA
226 push %cs # Read from
227 callw xread.1 # disk
228 jnc return # If success, return
229 mov $msg_read,%si # Otherwise, set the error
230 # message and fall through to
231 # the error routine
232/*
233 * Print out the error message pointed to by %ds:(%si) followed
234 * by a prompt, wait for a keypress, and then reboot the machine.
235 */
236error: callw putstr # Display message
237 mov $prompt,%si # Display
238 callw putstr # prompt
239 xorb %ah,%ah # BIOS: Get
240 int $0x16 # keypress
241 movw $0x1234, BDA_BOOT # Do a warm boot
|
243/*
244 * Display a null-terminated string using the BIOS output.
245 */
246putstr.0: mov $0x7,%bx # Page:attribute
247 movb $0xe,%ah # BIOS: Display
248 int $0x10 # character
249putstr: lodsb # Get char
250 testb %al,%al # End of string?
251 jne putstr.0 # No
252
253/*
254 * Overused return code. ereturn is used to return an error from the
255 * read function. Since we assume putstr succeeds, we (ab)use the
256 * same code when we return from putstr.
257 */
258ereturn: movb $0x1,%ah # Invalid
259 stc # argument
260return: retw # To caller
261/*
262 * Reads sectors from the disk. If EDD is enabled, then check if it is
263 * installed and use it if it is. If it is not installed or not enabled, then
264 * fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
265 * fetch the drive parameters from the BIOS and divide it out ourselves.
266 * Call with:
267 *
268 * %dl - byte - drive number
269 * stack - 10 bytes - EDD Packet
270 */
271read: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
272 jz read.1 # No, use CHS
273 cmpb $0x80,%dl # Hard drive?
274 jb read.1 # No, use CHS
275 mov $0x55aa,%bx # Magic
276 push %dx # Save
277 movb $0x41,%ah # BIOS: Check
278 int $0x13 # extensions present
279 pop %dx # Restore
280 jc read.1 # If error, use CHS
281 cmp $0xaa55,%bx # Magic?
282 jne read.1 # No, so use CHS
283 testb $0x1,%cl # Packet interface?
284 jz read.1 # No, so use CHS
285 mov %bp,%si # Disk packet
286 movb $0x42,%ah # BIOS: Extended
287 int $0x13 # read
288 retw # To caller
289read.1: push %dx # Save
290 movb $0x8,%ah # BIOS: Get drive
291 int $0x13 # parameters
292 movb %dh,%ch # Max head number
293 pop %dx # Restore
294 jc return # If error
295 andb $0x3f,%cl # Sectors per track
296 jz ereturn # If zero
297 cli # Disable interrupts
298 mov 0x8(%bp),%eax # Get LBA
299 push %dx # Save
300 movzbl %cl,%ebx # Divide by
301 xor %edx,%edx # sectors
302 div %ebx # per track
303 movb %ch,%bl # Max head number
304 movb %dl,%ch # Sector number
305 inc %bx # Divide by
306 xorb %dl,%dl # number
307 div %ebx # of heads
308 movb %dl,%bh # Head number
309 pop %dx # Restore
310 cmpl $0x3ff,%eax # Cylinder number supportable?
311 sti # Enable interrupts
312 ja ereturn # No, return an error
313 xchgb %al,%ah # Set up cylinder
314 rorb $0x2,%al # number
315 orb %ch,%al # Merge
316 inc %ax # sector
317 xchg %ax,%cx # number
318 movb %bh,%dh # Head number
319 subb %ah,%al # Sectors this track
320 mov 0x2(%bp),%ah # Blocks to read
321 cmpb %ah,%al # To read
322 jb read.2 # this
323#ifdef TRACK_AT_A_TIME
324 movb %ah,%al # track
325#else
326 movb $1,%al # one sector
327#endif
328read.2: mov $0x5,%di # Try count
329read.3: les 0x4(%bp),%bx # Transfer buffer
330 push %ax # Save
331 movb $0x2,%ah # BIOS: Read
332 int $0x13 # from disk
333 pop %bx # Restore
334 jnc read.4 # If success
335 dec %di # Retry?
336 jz read.6 # No
337 xorb %ah,%ah # BIOS: Reset
338 int $0x13 # disk system
339 xchg %bx,%ax # Block count
340 jmp read.3 # Continue
341read.4: movzbw %bl,%ax # Sectors read
342 add %ax,0x8(%bp) # Adjust
343 jnc read.5 # LBA,
344 incw 0xa(%bp) # transfer
345read.5: shlb %bl # buffer
346 add %bl,0x5(%bp) # pointer,
347 sub %al,0x2(%bp) # block count
348 ja read.1 # If not done
349read.6: retw # To caller
350
351/* Messages */
352
353msg_read: .asciz "Read"
354msg_part: .asciz "Boot"
355
356prompt: .asciz " error\r\n"
357
358flags: .byte FLAGS # Flags
359
360 .org PRT_OFF,0x90
361
362/* Partition table */
363
364 .fill 0x30,0x1,0x0
365part4: .byte 0x80, 0x00, 0x01, 0x00
366 .byte 0xa5, 0xfe, 0xff, 0xff
367 .byte 0x00, 0x00, 0x00, 0x00
368 .byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
369
370 .word 0xaa55 # Magic number
| 243/*
244 * Display a null-terminated string using the BIOS output.
245 */
246putstr.0: mov $0x7,%bx # Page:attribute
247 movb $0xe,%ah # BIOS: Display
248 int $0x10 # character
249putstr: lodsb # Get char
250 testb %al,%al # End of string?
251 jne putstr.0 # No
252
253/*
254 * Overused return code. ereturn is used to return an error from the
255 * read function. Since we assume putstr succeeds, we (ab)use the
256 * same code when we return from putstr.
257 */
258ereturn: movb $0x1,%ah # Invalid
259 stc # argument
260return: retw # To caller
261/*
262 * Reads sectors from the disk. If EDD is enabled, then check if it is
263 * installed and use it if it is. If it is not installed or not enabled, then
264 * fall back to using CHS. Since we use a LBA, if we are using CHS, we have to
265 * fetch the drive parameters from the BIOS and divide it out ourselves.
266 * Call with:
267 *
268 * %dl - byte - drive number
269 * stack - 10 bytes - EDD Packet
270 */
271read: testb $FL_PACKET,%cs:MEM_REL+flags-start # LBA support enabled?
272 jz read.1 # No, use CHS
273 cmpb $0x80,%dl # Hard drive?
274 jb read.1 # No, use CHS
275 mov $0x55aa,%bx # Magic
276 push %dx # Save
277 movb $0x41,%ah # BIOS: Check
278 int $0x13 # extensions present
279 pop %dx # Restore
280 jc read.1 # If error, use CHS
281 cmp $0xaa55,%bx # Magic?
282 jne read.1 # No, so use CHS
283 testb $0x1,%cl # Packet interface?
284 jz read.1 # No, so use CHS
285 mov %bp,%si # Disk packet
286 movb $0x42,%ah # BIOS: Extended
287 int $0x13 # read
288 retw # To caller
289read.1: push %dx # Save
290 movb $0x8,%ah # BIOS: Get drive
291 int $0x13 # parameters
292 movb %dh,%ch # Max head number
293 pop %dx # Restore
294 jc return # If error
295 andb $0x3f,%cl # Sectors per track
296 jz ereturn # If zero
297 cli # Disable interrupts
298 mov 0x8(%bp),%eax # Get LBA
299 push %dx # Save
300 movzbl %cl,%ebx # Divide by
301 xor %edx,%edx # sectors
302 div %ebx # per track
303 movb %ch,%bl # Max head number
304 movb %dl,%ch # Sector number
305 inc %bx # Divide by
306 xorb %dl,%dl # number
307 div %ebx # of heads
308 movb %dl,%bh # Head number
309 pop %dx # Restore
310 cmpl $0x3ff,%eax # Cylinder number supportable?
311 sti # Enable interrupts
312 ja ereturn # No, return an error
313 xchgb %al,%ah # Set up cylinder
314 rorb $0x2,%al # number
315 orb %ch,%al # Merge
316 inc %ax # sector
317 xchg %ax,%cx # number
318 movb %bh,%dh # Head number
319 subb %ah,%al # Sectors this track
320 mov 0x2(%bp),%ah # Blocks to read
321 cmpb %ah,%al # To read
322 jb read.2 # this
323#ifdef TRACK_AT_A_TIME
324 movb %ah,%al # track
325#else
326 movb $1,%al # one sector
327#endif
328read.2: mov $0x5,%di # Try count
329read.3: les 0x4(%bp),%bx # Transfer buffer
330 push %ax # Save
331 movb $0x2,%ah # BIOS: Read
332 int $0x13 # from disk
333 pop %bx # Restore
334 jnc read.4 # If success
335 dec %di # Retry?
336 jz read.6 # No
337 xorb %ah,%ah # BIOS: Reset
338 int $0x13 # disk system
339 xchg %bx,%ax # Block count
340 jmp read.3 # Continue
341read.4: movzbw %bl,%ax # Sectors read
342 add %ax,0x8(%bp) # Adjust
343 jnc read.5 # LBA,
344 incw 0xa(%bp) # transfer
345read.5: shlb %bl # buffer
346 add %bl,0x5(%bp) # pointer,
347 sub %al,0x2(%bp) # block count
348 ja read.1 # If not done
349read.6: retw # To caller
350
351/* Messages */
352
353msg_read: .asciz "Read"
354msg_part: .asciz "Boot"
355
356prompt: .asciz " error\r\n"
357
358flags: .byte FLAGS # Flags
359
360 .org PRT_OFF,0x90
361
362/* Partition table */
363
364 .fill 0x30,0x1,0x0
365part4: .byte 0x80, 0x00, 0x01, 0x00
366 .byte 0xa5, 0xfe, 0xff, 0xff
367 .byte 0x00, 0x00, 0x00, 0x00
368 .byte 0x50, 0xc3, 0x00, 0x00 # 50000 sectors long, bleh
369
370 .word 0xaa55 # Magic number
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