1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
|
/*
* Copyright (c) 2008 Luigi Rizzo (mostly documentation)
* Copyright (c) 2002 Bruce M. Simpson
* Copyright (c) 1998 Robert Nordier
* All rights reserved.
*
* Redistribution and use in source and binary forms are freely
* permitted provided that the above copyright notice and this
* paragraph and the following disclaimer are duplicated in all
* such forms.
*
* This software is provided "AS IS" and without any express or
* implied warranties, including, without limitation, the implied
* warranties of merchantability and fitness for a particular
* purpose.
*
* $FreeBSD$
*/
/* build options: */
#ifdef SIO /* use serial console on COM1. */
#endif
#ifdef PXE /* enable PXE/INT18 booting with F6 */
#endif
#ifdef CHECK_DRIVE /* make sure we boot from a HD. */
#endif
#ifdef ONLY_F_KEYS /* Only F1..F6, no digits on console */
#endif
#ifdef TEST /* enable some test code */
#ifndef ONLY_F_KEYS
#define ONLY_F_KEYS /* make room for the test code */
#endif
#endif
/*
* Note - this code uses many tricks to save space and fit in one sector.
* This includes using side effects of certain instructions, reusing
* register values from previous operations, etc.
* Be extremely careful when changing the code, even for simple things.
*/
/*
* BOOT BLOCK STRUCTURE
*
* This code implements a Master Boot Record (MBR) for an Intel/PC disk.
* It is 512 bytes long and it is normally loaded by the BIOS (or another
* bootloader) at 0:0x7c00. This code depends on %cs:%ip being 0:0x7c00
*
* The initial chunk of instructions is used as a signature by external
* tools (e.g. boot0cfg) which can manipulate the block itself.
*
* The area at offset 0x1b2 contains a magic string ('Drive '), also
* used as a signature to detect the block, and some variables that can
* be updated by boot0cfg (and optionally written back to the disk).
* These variables control the operation of the bootloader itself,
* e.g. which partitions to enable, the timeout, the use of LBA
* (called 'packet') or CHS mode, whether to force a drive number,
* and whether to write back the user's selection back to disk.
*
* As in every Master Boot Record, the partition table is at 0x1be,
* made of four 16-byte entries each containing:
*
* OFF SIZE DESCRIPTION
* 0 1 status (0x80: bootable, 0: non bootable)
* 1 3 start sector CHS
* 8:head, 6:sector, 2:cyl bit 9..8, 8:cyl bit 7..0
* 4 1 partition type
* 5 3 end sector CHS
* 8 4 LBA of first sector
* 12 4 partition size in sectors
*
* and followed by the two bytes 0x55, 0xAA (MBR signature).
*/
/*
* BOOT BLOCK OPERATION
*
* On entry, the registers contain the following values:
*
* %cs:%ip 0:0x7c00
* %dl drive number (0x80, 0x81, ... )
* %si pointer to the partition table from which we were loaded.
* Some boot code (e.g. syslinux) use this info to relocate
* themselves, so we want to pass a valid one to the next stage.
* NOTE: the use of %is is not a standard.
*
* This boot block first relocates itself at a different address (0:0x600),
* to free the space at 0:0x7c00 for the next stage boot block.
*
* It then initializes some memory at 0:0x800 and above (pointed by %bp)
* to store the original drive number (%dl) passed to us, and to construct a
* fake partition entry. The latter is used by the disk I/O routine and,
* in some cases, passed in %si to the next stage boot code.
*
* The variables at 0x1b2 are accessed as negative offsets from %bp.
*
* After the relocation, the code scans the partition table printing
* out enabled partition or disks, and waits for user input.
*
* When a partition is selected, or a timeout expires, the currently
* selected partition is used to load the next stage boot code,
* %dl and %si are set appropriately as when we were called, and
* control is transferred to the newly loaded code at 0:0x7c00.
*/
/*
* CONSTANTS
*
* NHRDRV is the address in segment 0 where the BIOS writes the
* total number of hard disks in the system.
* LOAD is the original load address and cannot be changed.
* ORIGIN is the relocation address. If you change it, you also need
* to change the value passed to the linker in the Makefile
* PRT_OFF is the location of the partition table (from the MBR standard).
* B0_OFF is the location of the data area, known to boot0cfg so
* it cannot be changed.
* MAGIC is the signature of a boot block.
*/
.set NHRDRV,0x475 # Number of hard drives
.set ORIGIN,0x600 # Execution address
.set LOAD,0x7c00 # Load address
.set PRT_OFF,0x1be # Partition table
.set B0_OFF,0x1b2 # Offset of boot0 data
.set MAGIC,0xaa55 # Magic: bootable
.set KEY_ENTER,0x1c # Enter key scan code
.set KEY_F1,0x3b # F1 key scan code
.set KEY_1,0x02 # #1 key scan code
.set ASCII_BEL,'#' # ASCII code for <BEL>
.set ASCII_CR,0x0D # ASCII code for <CR>
/*
* Offsets of variables in the block at B0_OFF, and in the volatile
* data area, computed as displacement from %bp.
* We need to define them as constant as the assembler cannot
* compute them in its single pass.
*/
.set _NXTDRV, -0x48 # Next drive
.set _OPT, -0x47 # Default option
.set _SETDRV, -0x46 # Drive to force
.set _FLAGS, -0x45 # Flags
.set SETDRV, 0x20 # the 'setdrv' flag
.set NOUPDATE, 0x40 # the 'noupdate' flag
.set USEPACKET, 0x80 # the 'packet' flag
.set _TICKS, -0x44 # Timeout ticks
.set _FAKE,0x0 # Fake partition table
.set _MNUOPT, 0x10 # Saved menu entries
.set TLEN, (desc_ofs - bootable_ids) # size of bootable ids
.globl start # Entry point
.code16 # This runs in real mode
/*
* MAIN ENTRY POINT
* Initialise segments and registers to known values.
* segments start at 0.
* The stack is immediately below the address we were loaded to.
* NOTE: the initial section of the code (up to movw $LOAD,%sp)
* is used by boot0cfg, together with the 'Drive ' string and
* the 0x55, 0xaa at the end, as an identifier for version 1.0
* of the boot code. Do not change it.
* In version 1.0 the parameter table (_NEXTDRV etc) is at 0x1b9
*/
start: cld # String ops inc
xorw %ax,%ax # Zero
movw %ax,%es # Address
movw %ax,%ds # data
movw %ax,%ss # Set up
movw $LOAD,%sp # stack
/*
* Copy this code to the address it was linked for, 0x600 by default.
*/
movw %sp,%si # Source
movw $start,%di # Destination
movw $0x100,%cx # Word count
rep # Relocate
movsw # code
/*
* After the code, (i.e. at %di+0, 0x800) create a partition entry,
* initialized to LBA 0 / CHS 0:0:1.
* Set %bp to point to the partition and also, with negative offsets,
* to the variables embedded in the bootblock (nextdrv and so on).
*/
movw %di,%bp # Address variables
movb $0x8,%cl # Words to clear
rep # Zero
stosw # them
incb -0xe(%di) # Set the S field to 1
jmp main-LOAD+ORIGIN # Jump to relocated code
main:
#if defined(SIO) && COMSPEED != 0
/*
* Init the serial port. bioscom preserves the driver number in DX.
*/
movw $COMSPEED,%ax # defined by Makefile
callw bioscom
#endif
/*
* If the 'setdrv' flag is set in the boot sector, use the drive
* number from the boot sector at 'setdrv_num'.
* Optionally, do the same if the BIOS gives us an invalid number
* (note though that the override prevents booting from a floppy
* or a ZIP/flash drive in floppy emulation).
* The test costs 4 bytes of code so it is disabled by default.
*/
testb $SETDRV,_FLAGS(%bp) # Set drive number?
#ifndef CHECK_DRIVE /* disable drive checks */
jz save_curdrive # no, use the default
#else
jnz disable_update # Yes
testb %dl,%dl # Drive number valid?
js save_curdrive # Possibly (0x80 set)
#endif
/*
* Disable updates if the drive number is forced.
*/
disable_update: orb $NOUPDATE,_FLAGS(%bp) # Disable updates
movb _SETDRV(%bp),%dl # Use stored drive number
/*
* Whatever drive we decided to use, store it at (%bp). The byte
* is normally used for the state of the partition (0x80 or 0x00),
* but we abuse it as it is very convenient to access at offset 0.
* The value is read back after 'check_selection'
*/
save_curdrive: movb %dl, (%bp) # Save drive number
pushw %dx # Also in the stack
#ifdef TEST /* test code, print internal bios drive */
rolb $1, %dl
movw $drive, %si
call putkey
#endif
callw putn # Print a newline
/*
* Start out with a pointer to the 4th byte of the first table entry
* so that after 4 iterations it's beyond the end of the sector
* and beyond a 256 byte boundary. We use the latter trick to check for
* end of the loop without using an extra register (see start.5).
*/
movw $(partbl+0x4),%bx # Partition table (+4)
xorw %dx,%dx # Item number
/*
* Loop around on the partition table, printing values until we
* pass a 256 byte boundary.
*/
read_entry: movb %ch,-0x4(%bx) # Zero active flag (ch == 0)
btw %dx,_FLAGS(%bp) # Entry enabled?
jnc next_entry # No
/*
* Lookup type in the 'non_bootable_ids' table, skip matching entries.
* This is implemented is by setting %di to the start of the
* exclude table, and %cl to the length of the table itself. After the
* 'repne scasb' the zero flag is set if we found a match.
* If not, %di points to the beginning of the 'valid' types,
* which is what we need for the next check.
*/
movb (%bx),%al # Load type
movw $non_bootable_ids,%di # Lookup tables
movb $(bootable_ids-non_bootable_ids),%cl # length
repne # Exclude
scasb # partition?
je next_entry # Yes, ignore it
/*
* Now scan the table of bootable ids, which starts at %di and has
* length TLEN. On a match, %di points to the element following the
* match; the corresponding offset to the description is $(TLEN-1)
* bytes ahead. If we don't find a match, we hit the 'unknown' entry.
*/
movb $(TLEN),%cl # Number of entries
repne # Locate
scasb # type
/*
* Get the matching element in the next array.
* The byte at $(TLEN-1)(%di) contains the offset of the description
* string from %di, so we add the number and print the string.
*/
addw $(TLEN-1), %di # Adjust
movb (%di),%cl # Partition
addw %cx,%di # description
callw putx # Display it
next_entry: incw %dx # Next item
addb $0x10,%bl # Next entry
jnc read_entry # Till done
/*
* We are past a 256 byte boundary: the partition table is finished.
* Add one to the drive number and check it is valid.
* Note that if we started from a floppy, %dl was 0 so we still
* get an entry for the next drive, which is the first Hard Disk.
*/
popw %ax # Drive number
subb $0x80-0x1,%al # Does next
cmpb NHRDRV,%al # drive exist? (from BIOS?)
jb print_drive # Yes
/*
* If this is the only drive, don't display it as an option.
*/
decw %ax # Already drive 0?
jz print_prompt # Yes
/*
* If it was illegal or we cycled through them, go back to drive 0.
*/
xorb %al,%al # Drive 0
/*
* Whatever drive we selected, make it an ascii digit and save it
* back to the "nxtdrv" location in case we want to save it to disk.
* This digit is also part of the printed drive string, so add 0x80
* to indicate end of string.
*/
print_drive: addb $'0'|0x80,%al # Save next
movb %al,_NXTDRV(%bp) # drive number
movw $drive,%di # Display
callw putx # item
/*
* Menu is complete, display a prompt followed by current selection.
* 'decw %si' makes the register point to the space after 'Default: '
* so we do not see an extra CRLF on the screen.
*/
print_prompt: movw $prompt,%si # Display
callw putstr # prompt
movb _OPT(%bp),%dl # Display
decw %si # default
callw putkey # key
jmp start_input # Skip beep
/*
* Here we have the code waiting for user input or a timeout.
*/
beep: movb $ASCII_BEL,%al # Input error, print or beep
callw putchr
start_input:
/*
* Actual Start of input loop. Take note of time
*/
xorb %ah,%ah # BIOS: Get
int $0x1a # system time
movw %dx,%di # Ticks when
addw _TICKS(%bp),%di # timeout
read_key:
/*
* Busy loop, looking for keystrokes but keeping one eye on the time.
*/
#ifndef SIO
movb $0x1,%ah # BIOS: Check
int $0x16 # for keypress
#else /* SIO */
movb $0x03,%ah # BIOS: Read COM
call bioscom
testb $0x01,%ah # Check line status
# (bit 1 indicates input)
#endif /* SIO */
jnz got_key # Have input
xorb %ah,%ah # BIOS: int 0x1a, 00
int $0x1a # get system time
cmpw %di,%dx # Timeout?
jb read_key # No
/*
* Timed out or default selection
*/
use_default: movb _OPT(%bp),%al # Load default
jmp check_selection # Join common code
/*
* Get the keystroke.
* ENTER or CR confirm the current selection (same as a timeout).
* Otherwise convert F1..F6 (or '1'..'6') to 0..5 and check if the
* selection is valid.
* The SIO code uses ascii chars, the console code uses scancodes.
*/
got_key:
#ifndef SIO
xorb %ah,%ah # BIOS: int 0x16, 00
int $0x16 # get keypress
movb %ah,%al # move scan code to %al
cmpb $KEY_ENTER,%al
#else
movb $0x02,%ah # BIOS: Receive
call bioscom
cmpb $ASCII_CR,%al
#endif
je use_default # enter -> default
/*
* Check if the key is acceptable, and loop back if not.
* The console (non-SIO) code looks at scancodes and accepts
* both F1..F6 and 1..6 (the latter costs 6 bytes of code),
* relying on the fact that F1..F6 have higher scancodes than 1..6
* The SIO code only takes 1..6
*/
#ifdef SIO /* SIO mode, use ascii values */
subb $'1',%al # Subtract '1' ascii code
#else /* console mode -- use scancodes */
subb $KEY_F1,%al /* Subtract F1 scan code */
#if !defined(ONLY_F_KEYS)
cmpb $0x5,%al # F1..F6
jna 3f # Yes
subb $(KEY_1 - KEY_F1),%al # Less #1 scan code
3:
#endif /* ONLY_F_KEYS */
#endif /* SIO */
cmpb $0x5,%al # F1..F6 or 1..6 ?
#ifdef PXE /* enable PXE/INT18 using F6 */
jne 1f;
int $0x18 # found F6, try INT18
1:
#endif /* PXE */
jae beep # Not in F1..F5, beep
check_selection:
/*
* We have a selection. If it's a bad selection go back to complain.
* The bits in MNUOPT were set when the options were printed.
* Anything not printed is not an option.
*/
cbtw # Extend (%ah=0 used later)
btw %ax,_MNUOPT(%bp) # Option enabled?
jnc beep # No
/*
* Save the info in the original tables
* for rewriting to the disk.
*/
movb %al,_OPT(%bp) # Save option
/*
* Make %si and %bx point to the fake partition at LBA 0 (CHS 0:0:1).
* Because the correct address is already in %bp, just use it.
* Set %dl with the drive number saved in byte 0.
* If we have pressed F5 or 5, then this is a good, fake value
* to present to the next stage boot code.
*/
movw %bp,%si # Partition for write
movb (%si),%dl # Drive number, saved above
movw %si,%bx # Partition for read
cmpb $0x4,%al # F5/#5 pressed?
pushf # Save results for later
je 1f # Yes, F5
/*
* F1..F4 was pressed, so make %bx point to the currently
* selected partition, and leave the drive number unchanged.
*/
shlb $0x4,%al # Point to
addw $partbl,%ax # selected
xchgw %bx,%ax # partition
movb $0x80,(%bx) # Flag active
/*
* If not asked to do a write-back (flags 0x40) don't do one.
* Around the call, save the partition pointer to %bx and
* restore to %si which is where the next stage expects it.
*/
1: pushw %bx # Save
testb $NOUPDATE,_FLAGS(%bp) # No updates?
jnz 2f # skip update
movw $start,%bx # Data to write
movb $0x3,%ah # Write sector
callw intx13 # to disk
2: popw %si # Restore
/*
* If going to next drive, replace drive with selected one.
* Remember to un-ascii it. Hey 0x80 is already set, cool!
*/
popf # Restore %al test results
jne 3f # If not F5/#5
movb _NXTDRV(%bp),%dl # Next drive
subb $'0',%dl # number
/*
* Load selected bootsector to the LOAD location in RAM. If read
* fails or there is no 0x55aa marker, treat it as a bad selection.
*/
3: movw $LOAD,%bx # Address for read
movb $0x2,%ah # Read sector
callw intx13 # from disk
jc beep # If error
cmpw $MAGIC,0x1fe(%bx) # Bootable?
jne beep # No
pushw %si # Save ptr to selected part.
callw putn # Leave some space
popw %si # Restore, next stage uses it
jmp *%bx # Invoke bootstrap
/*
* Display routines
* putkey prints the option selected in %dl (F1..F5 or 1..5) followed by
* the string at %si
* putx: print the option in %dl followed by the string at %di
* also record the drive as valid.
* puts: print the string at %si followed by a crlf
* putn: print a crlf
* putstr: print the string at %si
* putchr: print the char in al
*/
putkey:
#ifndef SIO
movb $'F',%al # Display
callw putchr # 'F'
#endif
movb $'1',%al # Prepare
addb %dl,%al # digit
jmp putstr.1 # Display the rest
/*
* Display the option and record the drive as valid in the options.
* That last point is done using the btsw instruction which does
* a test and set. We don't care for the test part.
*/
putx: btsw %dx,_MNUOPT(%bp) # Enable menu option
movw $item,%si # Display
callw putkey # key
movw %di,%si # Display the rest
puts: callw putstr # Display string
putn: movw $crlf,%si # To next line
putstr: lodsb # Get byte
testb $0x80,%al # End of string?
jnz putstr.2 # Yes
putstr.1: callw putchr # Display char
jmp putstr # Continue
putstr.2: andb $~0x80,%al # Clear MSB
putchr:
#ifndef SIO
pushw %bx # Save
movw $0x7,%bx # Page:attribute
movb $0xe,%ah # BIOS: Display
int $0x10 # character
popw %bx # Restore
#else /* SIO */
movb $0x01,%ah # BIOS: Send
bioscom:
pushw %dx # Save
xorw %dx,%dx # Use COM1
int $0x14 # Character
popw %dx # Restore
#endif /* SIO */
retw # To caller
/* One-sector disk I/O routine */
/*
* %dl: drive, %si partition entry, %es:%bx transfer buffer.
* Load the CHS values and possibly the LBA address from the block
* at %si, and use the appropriate method to load the sector.
* Don't use packet mode for a floppy.
*/
intx13: # Prepare CHS parameters
movb 0x1(%si),%dh # Load head
movw 0x2(%si),%cx # Load cylinder:sector
movb $0x1,%al # Sector count
pushw %si # Save
movw %sp,%di # Save
#ifndef CHECK_DRIVE /* floppy support */
testb %dl, %dl # is this a floppy ?
jz 1f # Yes, use CHS mode
#endif
testb $USEPACKET,_FLAGS(%bp) # Use packet interface?
jz 1f # No
pushl $0x0 # Set the
pushl 0x8(%si) # LBA address
pushw %es # Set the transfer
pushw %bx # buffer address
push $0x1 # Block count
push $0x10 # Packet size
movw %sp,%si # Packet pointer
decw %ax # Verify off
orb $0x40,%ah # Use disk packet
1: int $0x13 # BIOS: Disk I/O
movw %di,%sp # Restore
popw %si # Restore
retw # To caller
/*
* Various menu strings. 'item' goes after 'prompt' to save space.
* Also use shorter versions to make room for the PXE/INT18 code.
*/
#ifdef PXE
prompt: .ascii "\nBoot:"
item: .ascii " "; .byte ' '|0x80
#else
prompt: .ascii "\nDefault:"
item: .ascii " "; .byte ' '|0x80
#endif
crlf: .ascii "\r"; .byte '\n'|0x80
/* Partition type tables */
non_bootable_ids:
/*
* These entries identify invalid or NON BOOT types and partitions.
* 0: empty, 5: DOS3 ext. partition, 0xf: WIN95 ext partition
*/
.byte 0x0, 0x5, 0xf
bootable_ids:
/*
* These values indicate bootable types we know the names of.
* 1: FAT12, 4: FAT16 <32M, 6: FAT16 > 32M, 7: NTFS
* 0xb: FAT32, 0xc: FAT32-LBA, 0xe: FAT16-LBA,
* 0x83: linux, 0xa5: FreeBSD, 0xa6: netbsd, 0xa9:openbsd
*/
.byte 0x1, 0x6, 0x7, 0xb, 0xc, 0xe, 0x83
.byte 0xa5, 0xa6, 0xa9, 0x4
desc_ofs:
/*
* Offsets that match the known types above, used to point to the
* actual partition name. The last entry must point to os_misc,
* which is used for non-matching names.
*/
.byte os_dos-. # 1, DOS
.byte os_dos-. # 6, DOS/WIN
.byte os_win-. # 7, Windows
.byte os_win-. # 11, Windows
.byte os_win-. # 12, Windows
.byte os_win-. # 14, Windows
.byte os_linux-. # 131, Linux
.byte os_freebsd-. # 165, FreeBSD
.byte os_bsd-. # 166, OpenBSD
.byte os_bsd-. # 169, NetBSD
.byte os_dos-. # 4, DOS
.byte os_misc-. # Unknown
/*
* And here are the strings themselves. The last byte of
* the string has bit 7 set.
*/
os_misc: .byte '?'|0x80
os_dos:
#if !defined(TEST) /* DOS string only if room */
.ascii "DO"; .byte 'S'|0x80
#endif
os_win: .ascii "WI"; .byte 'N'|0x80
os_linux: .ascii "Linu"; .byte 'x'|0x80
os_freebsd: .ascii "Free"
os_bsd: .ascii "BS"; .byte 'D'|0x80
.org B0_OFF,0x90
/*
* The boot0 version 1.0 parameter table.
* Do not move it nor change the "Drive " string, boot0cfg
* uses its offset and content to identify the boot sector.
* The other fields are sometimes changed before writing back to the drive
* Be especially careful that nxtdrv: must come after drive:, as it
* is part of the same string.
*/
drive: .ascii "Drive "
nxtdrv: .byte 0x0 # Next drive number
opt: .byte 0x0 # Option
setdrv_num: .byte 0x80 # Drive to force
flags: .byte FLAGS # Flags
ticks: .word TICKS # Delay
.org PRT_OFF
/*
* Here is the 64 byte partition table that fdisk would fiddle with.
*/
partbl: .fill 0x40,0x1,0x0 # Partition table
.word MAGIC # Magic number
.org 0x200 # again, safety check
endblock:
|