wok view BootProg/stuff/boot16.asm @ rev 24491
Add some current_version
| author | Pascal Bellard <pascal.bellard@slitaz.org> |
|---|---|
| date | Fri Feb 18 22:59:06 2022 +0000 (2022-02-18) |
| parents | d211771a0500 |
| children | d1f31f5f6401 |
line source
1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
2 ;; ;;
3 ;; "BootProg" Loader v 1.5 by Alexey Frunze (c) 2000-2015 ;;
4 ;; 2-clause BSD license. ;;
5 ;; ;;
6 ;; ;;
7 ;; How to Compile: ;;
8 ;; ~~~~~~~~~~~~~~~ ;;
9 ;; nasm boot16.asm -f bin -o boot16.bin ;;
10 ;; ;;
11 ;; ;;
12 ;; Features: ;;
13 ;; ~~~~~~~~~ ;;
14 ;; - FAT12 and FAT16 supported using BIOS int 13h function 42h or 02h. ;;
15 ;; ;;
16 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
17 ;; from the root directory of a disk and transfers control to it ;;
18 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
19 ;; Its maximum size can be up to 635KB without Extended BIOS Data area. ;;
20 ;; ;;
21 ;; - Prints an error if the file isn't found or couldn't be read ;;
22 ;; ("File not found" or "Read error") ;;
23 ;; and waits for a key to be pressed, then executes the Int 19h ;;
24 ;; instruction and lets the BIOS continue bootstrap. ;;
25 ;; ;;
26 ;; - cpu 8086 is supported ;;
27 ;; ;;
28 ;; ;;
29 ;; Known Bugs: ;;
30 ;; ~~~~~~~~~~~ ;;
31 ;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
32 ;; on the following types of diskettes (FAT12): ;;
33 ;; - 360KB 5"25 ;;
34 ;; - 1.2MB 5"25 ;;
35 ;; - 1.44MB 3"5 ;;
36 ;; on my HDD (FAT16). ;;
37 ;; ;;
38 ;; ;;
39 ;; Memory Layout: ;;
40 ;; ~~~~~~~~~~~~~~ ;;
41 ;; The diagram below shows the typical memory layout. The actual location ;;
42 ;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
43 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
44 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
45 ;; ;;
46 ;; physical address ;;
47 ;; +------------------------+ 00000H ;;
48 ;; | Interrupt Vector Table | ;;
49 ;; +------------------------+ 00400H ;;
50 ;; | BIOS Data Area | ;;
51 ;; +------------------------+ 00500H ;;
52 ;; | PrtScr Status / Unused | ;;
53 ;; +------------------------+ 00600H ;;
54 ;; | Loaded Image | ;;
55 ;; +------------------------+ nnnnnH ;;
56 ;; | Available Memory | ;;
57 ;; +------------------------+ A0000H - 512 - 3KB ;;
58 ;; | Boot Sector | ;;
59 ;; +------------------------+ A0000H - 3KB ;;
60 ;; | 3KB Boot Stack | ;;
61 ;; +------------------------+ A0000H ;;
62 ;; | Video RAM | ;;
63 ;; ;;
64 ;; ;;
65 ;; Boot Image Startup (register values): ;;
66 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
67 ;; dl = BIOS boot drive number (e.g. 0, 80H) ;;
68 ;; cs:ip = program entry point ;;
69 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
70 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
71 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
72 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
73 ;; cs:ip and ss:sp depends on EXE header ;;
74 ;; Magic numbers: ;;
75 ;; si = 16381 (prime number 2**14-3) ;;
76 ;; di = 32749 (prime number 2**15-19) ;;
77 ;; bp = 65521 (prime number 2**16-15) ;;
78 ;; The magic numbers let the program know whether it has been loaded by ;;
79 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
80 ;; metal and MS-DOS programs. ;;
81 ;; ;;
82 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
84 %define bx(label) bx+label-boot
86 [BITS 16]
87 [CPU 8086]
89 ImageLoadSeg equ 60h
90 StackSize equ 3072 ; Stack + cluster list
92 [SECTION .text]
93 [ORG 0]
95 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
96 ;; Boot sector starts here ;;
97 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
99 boot:
100 jmp short start ; MS-DOS/Windows checks for this jump
101 nop
102 bsOemName DB "BootProg" ; 0x03
104 ;;;;;;;;;;;;;;;;;;;;;
105 ;; BPB starts here ;;
106 ;;;;;;;;;;;;;;;;;;;;;
108 bpbBytesPerSector DW 0 ; 0x0B
109 bpbSectorsPerCluster DB 0 ; 0x0D
110 bpbReservedSectors DW 0 ; 0x0E
111 bpbNumberOfFATs DB 0 ; 0x10
112 bpbRootEntries DW 0 ; 0x11
113 bpbTotalSectors DW 0 ; 0x13
114 bpbMedia DB 0 ; 0x15
115 bpbSectorsPerFAT DW 0 ; 0x16
116 bpbSectorsPerTrack DW 0 ; 0x18
117 bpbHeadsPerCylinder DW 0 ; 0x1A
118 bpbHiddenSectors DD 0 ; 0x1C
119 bpbTotalSectorsBig DD 0 ; 0x20
121 ;;;;;;;;;;;;;;;;;;;
122 ;; BPB ends here ;;
123 ;;;;;;;;;;;;;;;;;;;
125 bsDriveNumber DB 0 ; 0x24
126 bsUnused DB 0 ; 0x25
127 bsExtBootSignature DB 0 ; 0x26
128 bsSerialNumber DD 0 ; 0x27
129 bsVolumeLabel DB "NO NAME " ; 0x2B
130 bsFileSystem DB "FAT12 " ; 0x36
132 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
133 ;; Boot sector code starts here ;;
134 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
136 start:
137 cld
139 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
140 ;; How much RAM is there? ;;
141 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
143 int 12h ; get conventional memory size (in KBs)
144 mov cx, 106h
145 shl ax, cl ; and convert it to 16-byte paragraphs
147 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
148 ;; Reserve memory for the boot sector and its stack ;;
149 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
151 sub ax, (512+StackSize) /16 ; reserve bytes for the code and the stack
152 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
153 mov ss, ax
154 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
156 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
157 ;; Copy ourselves to top of memory ;;
158 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
160 mov si, 7C00h
161 xor di, di
162 mov ds, di
163 mov [si], dx ; store BIOS boot drive number
164 rep movsw ; move 512 bytes (+ 12)
166 ;;;;;;;;;;;;;;;;;;;;;;
167 ;; Jump to the copy ;;
168 ;;;;;;;;;;;;;;;;;;;;;;
170 push es
171 mov cl, byte main
172 push cx
173 retf
175 main:
176 %if ImageLoadSeg != main-boot
177 %if ImageLoadSeg >= 100h
178 mov cx, ImageLoadSeg
179 %else
180 mov cl, ImageLoadSeg
181 %endif
182 %endif
183 push cx
185 ;;;;;;;;;;;;;;;;;;;;;;;;;;
186 ;; Get drive parameters ;;
187 ;; Update heads count ;;
188 ;; for current BIOS ;;
189 ;;;;;;;;;;;;;;;;;;;;;;;;;;
191 mov ah, 8
192 int 13h ; may destroy SI,BP, and DS registers
193 ; update AX,BL,CX,DX,DI, and ES registers
194 push cs
195 pop ds
196 xor bx, bx
198 and cx, byte 3Fh
199 cmp [bx(bpbSectorsPerTrack)], cx
200 jne BadParams ; verify updated and validity
201 mov al, dh
202 inc ax
203 mov [bpbHeadsPerCylinder], ax
204 BadParams:
206 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
207 ;; Load FAT (FAT12: 6KB max, FAT16: 128KB max) ;;
208 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
210 pop es ; ImageLoadSeg
211 push es
213 mul bx ; dx:ax = 0 = LBA (LBA are relative to FAT)
214 mov cx, word [bx(bpbSectorsPerFAT)]
216 call ReadCXSectors ; read fat and clear cx
218 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
219 ;; load the root directory in ;;
220 ;; its entirety (16KB max) ;;
221 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
223 mov ax, 32
225 mul word [bx(bpbRootEntries)]
226 div word [bx(bpbBytesPerSector)]
227 xchg ax, cx ; cx = root directory size in sectors, clear ax
229 mov al, [bpbNumberOfFATs]
230 mul bp ; [bx(bpbSectorsPerFAT)], set by ReadCXSectors
232 push es
233 call ReadCXSectors ; read root directory, clear cx and di
234 pop es
236 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
237 ;; Look for the COM/EXE file to load and run ;;
238 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
240 ; es:di -> root entries array
242 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
243 ;; Looks for the file/dir ProgramName ;;
244 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
245 ;; Input: ES:DI -> root directory array ;;
246 ;; Output: SI = cluster number ;;
247 ;; AX = file sector count ;;
248 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
250 FindNameCycle:
251 cmp byte [es:di], ch
252 je FindNameFailed ; end of root directory (NULL entry found)
253 push di
254 mov cl, 11
255 mov si, ProgramName ; ds:si -> program name
256 repe cmpsb
257 pop di
258 je FindNameFound
259 add di, byte 32
260 dec word [bx(bpbRootEntries)]
261 jnz FindNameCycle ; next root entry
263 FindNameFailed:
264 call Error
265 db "File not found."
267 FindNameFound:
268 push si
269 mov si, [es:di+1Ah] ; si = cluster no.
270 les ax, [es:di+1Ch] ; file size
271 mov dx, es
272 div word [bx(bpbBytesPerSector)]
273 cmp bx, dx ; sector aligned ?
274 adc ax, bx ; file last sector
275 pop di ; di = ClusterList
277 pop es ; ImageLoadSeg
278 push ax
280 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
281 ;; build cluster list ;;
282 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
283 ;; Input: ES:0 -> FAT ;;
284 ;; SI = first cluster ;;
285 ;; DI = cluster list :;
286 ;; CH = 0 ;;
287 ;; Output: SI = cluster list ;;
288 ;; CH = 0 ;;
289 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
291 push di ; up to 2 * 635K / BytesPerCluster bytes
292 mov cl, 12
293 ClusterLoop:
294 mov [di], si
296 mov ax, es ; ax = FAT segment = ImageLoadSeg
297 add si, si ; si = cluster * 2
298 jnc First64
299 mov ah, (1000h+ImageLoadSeg)>>8 ; adjust segment for 2nd part of FAT16
300 First64:
301 cmp [bx(bpbSectorsPerFAT)], cx ; 1..12 = FAT12, 16..256 = FAT16
302 mov ds, ax
303 jbe ReadClusterFat12
305 lodsw ; ax = next cluster
306 cmp ax, 0FFF8h
307 jmp short ReadClusterDone
309 ReadClusterFat12:
310 add si, [cs:di]
311 shr si, 1 ; si = cluster * 3 / 2
313 lodsw ; ax = next cluster
314 jnc ReadClusterEven
316 rol ax, cl
318 ReadClusterEven:
319 and ax, 0FFFh ; mask cluster value
320 cmp ax, 0FF8h
322 ReadClusterDone:
323 push cs
324 pop ds
325 inc di
326 inc di
327 xchg ax, si
328 jc ClusterLoop
329 pop si
330 pop di ; file size in sectors
332 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
333 ;; Load the entire file ;;
334 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
335 ;; Input: ES:0 -> buffer ;;
336 ;; SI = cluster list ;;
337 ;; DI = file sectors ;;
338 ;; CH = 0 ;;
339 ;; Output: BP:0 -> buffer ;;
340 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
342 push es
344 ReadClusters:
345 lodsw
346 dec ax
347 dec ax
349 mov cl, [bx(bpbSectorsPerCluster)]
350 mul cx ; cx = sector count (ch = 0)
352 add ax, bp ; LBA for cluster data
353 adc dx, bx ; dx:ax = LBA
355 call ReadSector ; clear cx
357 jne ReadClusters
359 pop bp ; ImageLoadSeg
361 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
362 ;; Type detection, .COM or .EXE? ;;
363 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
365 mov ds, bp ; bp=ds=seg the file is loaded to
367 add bp, [bx+08h] ; bp = image base
368 mov ax, [bx+06h] ; ax = reloc items
369 mov di, [bx+18h] ; di = reloc table pointer
371 cmp word [bx], 5A4Dh ; "MZ" signature?
372 je RelocateEXE ; yes, it's an EXE program
374 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
375 ;; Setup and run a .COM program ;;
376 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
377 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
379 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
380 mov ss, bp
381 xor sp, sp
382 push bp ; cs, ds and es
383 mov bh, 1 ; ip
384 jmp short Run
386 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
387 ;; Relocate, setup and run a .EXE program ;;
388 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
389 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
390 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
392 ReloCycle:
393 add [di+2], bp ; item seg (abs)
394 les si, [di] ; si = item ofs, es = item seg
395 add [es:si], bp ; fixup
396 scasw ; di += 2
397 scasw ; point to next entry
399 RelocateEXE:
400 dec ax ; 32768 max (128KB table)
401 jns ReloCycle ; leave with ax=0ffffh: both FCB in the
402 ; PSP don't have a valid drive identifier
403 les si, [bx+0Eh]
404 add si, bp
405 mov ss, si ; ss for EXE
406 mov sp, es ; sp for EXE
408 lea si, [bp-10h] ; ds and es both point to the segment
409 push si ; containing the PSP structure
411 add bp, [bx+16h] ; cs for EXE
412 mov bx, [bx+14h] ; ip for EXE
413 Run:
414 pop ds
415 push bp
416 push bx
417 push ds
418 pop es
420 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
421 ;; Set the magic numbers so the program knows that it ;;
422 ;; has been loaded by this bootsector and not by MS-DOS ;;
423 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
424 mov si, 16381 ; prime number 2**14-3
425 mov di, 32749 ; prime number 2**15-19
426 mov bp, 65521 ; prime number 2**16-15
428 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
429 ;; All done, transfer control to the program now ;;
430 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
431 retf
433 ReadCXSectors:
434 mov bp, cx
435 add bp, ax ; adjust LBA for cluster data
437 mov di, cx ; no file size limit
439 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
440 ;; Reads sectors using BIOS Int 13h ;;
441 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
442 ;; Input: DX:AX = LBA relative to FAT ;;
443 ;; BX = 0 ;;
444 ;; CX = sector count ;;
445 ;; DI = file sectors ;;
446 ;; ES:BX -> buffer address ;;
447 ;; Output: ES:BX -> next address ;;
448 ;; BX = 0 ;;
449 ;; CX or DI = 0 ;;
450 ;; DL = drive number ;;
451 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
453 ReadSector:
454 add ax, [bx(bpbHiddenSectors)]
455 adc dx, [bx(bpbHiddenSectors)+2]
456 add ax, [bx(bpbReservedSectors)]
458 push si
459 ReadSectorNext:
460 adc dx, bx
461 push di
462 push cx
464 push bx
465 push bx
466 push dx ; 32-bit LBA: up to 2TB
467 push ax
468 push es
469 push bx
470 inc bx ; sector count word = 1
471 push bx
472 dec bx
473 mov di, 16 ; packet size byte = 16, reserved byte = 0
474 push di
476 xchg ax, cx ; save low LBA
477 xchg ax, dx ; get high LBA
478 cwd ; clear dx (LBA offset <2TB)
479 div word [bx(bpbSectorsPerTrack)] ; up to 8GB disks
481 xchg ax, cx ; restore low LBA, save high LBA / SPT
482 div word [bx(bpbSectorsPerTrack)]
483 ; ax = LBA / SPT
484 ; dx = LBA % SPT = sector - 1
485 inc dx
487 xchg cx, dx ; restore high LBA / SPT, save sector no.
488 div word [bx(bpbHeadsPerCylinder)]
489 ; ax = (LBA / SPT) / HPC = cylinder
490 ; dx = (LBA / SPT) % HPC = head
491 mov ch, al
492 ; ch = LSB 0...7 of cylinder no.
493 mov al, 64
494 mul ah
495 or cl, al
496 ; cl = MSB 8...9 of cylinder no. + sector no.
497 mov dh, dl
498 ; dh = head no.
500 ReadSectorRetry:
501 mov dl, [bx]
502 ; dl = drive no.
503 mov ah, 42h ; ah = 42h = extended read function no.
504 mov si, sp
505 int 13h ; extended read sectors (DL, DS:SI)
506 jnc ReadSectorNextSegment
508 mov ax, 201h ; al = sector count = 1
509 ; ah = 2 = read function no.
510 int 13h ; read sectors (AL, CX, DX, ES:BX)
512 jnc ReadSectorNextSegment
513 cbw ; ah = 0 = reset function
514 int 13h ; reset drive (DL)
516 dec di
517 jnz ReadSectorRetry ; extra attempt
519 call Error
520 db "Read error."
522 ReadSectorNextSegment:
524 pop ax ; al = 16
525 mul byte [bx(bpbBytesPerSector)+1] ; = (bpbBytesPerSector/256)*16
526 pop cx ; sector count = 1
527 pop bx
528 add [si+6], ax ; adjust segment for next sector
529 pop es ; es:0 updated
530 pop ax
531 pop dx
532 pop di
533 pop di
535 add ax, cx ; adjust LBA for next sector
537 pop cx ; cluster sectors to read
538 pop di ; file sectors to read
539 dec di ; keep C
540 loopne ReadSectorNext ; until cluster sector count or file sector count is reached
541 pop si
542 mov dx, [bx] ; pass the BIOS boot drive to Run or Error
544 ret
546 ;;;;;;;;;;;;;;;;;;;;;;;;;;
547 ;; Error Messaging Code ;;
548 ;;;;;;;;;;;;;;;;;;;;;;;;;;
550 Error:
551 pop si
553 PutStr:
554 mov ah, 0Eh
555 mov bl, 7
556 lodsb
557 int 10h
558 cmp al, "."
559 jne PutStr
561 cbw
562 int 16h ; wait for a key...
563 int 19h ; bootstrap
565 Stop:
566 hlt
567 jmp short Stop
569 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
570 ;; Fill free space with zeroes ;;
571 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
573 times (512-13-($-$$)) db 0
575 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
576 ;; Name of the file to load and run ;;
577 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
579 ProgramName db "STARTUP BIN" ; name and extension each must be
580 ; padded with spaces (11 bytes total)
582 ;;;;;;;;;;;;;;;;;;;;;;;;;;
583 ;; End of the sector ID ;;
584 ;;;;;;;;;;;;;;;;;;;;;;;;;;
586 ClusterList dw 0AA55h ; BIOS checks for this ID