boot.lst

DOS SOURCE CODE,DOS-C started in 1988 as an experiment in writing device drivers in C for Microsof

    442
    443				     ;	     readDisk:	     Reads a number of sectors into memory.
    444				     ;
    445				     ;	     Call with:	     DX:AX = 32-bit DOS	sector number
    446				     ;			     DI	= number of sectors to read
    447				     ;			     ES:BX = destination buffer
    448				     ;			     ES	must be	64k aligned (1000h, 2000h etc).
    449				     ;
    450				     ;	     Returns:	     CF	set on error
    451				     ;			     ES:BX points one byte after the last byte read.
    452
    453	015E			     readDisk	     proc
    454	015E  56				     push    si
    455	015F  52		     read_next:	     push    dx
    456	0160  50				     push    ax
    457
    458						     ;
    459						     ; translate sector	number to BIOS parameters
    460						     ;
    461
    462						     ;
    463						     ; abs = sector			     offset in track
    464						     ;	   + head * sectPerTrack	     offset in cylinder
    465						     ;	   + track * sectPerTrack * nHeads   offset in platter
    466						     ;
    467						     ; t1     =	abs  /	sectPerTrack	     (ax has t1)
    468						     ; sector =	abs mod	sectPerTrack	     (cx has sector)
    469						     ;
    470	0161  F7 76 18				     div     word ptr sectPerTrack
    471	0164  8B CA				     mov     cx, dx
    472
    473						     ;
    474						     ; t1   = head + track * nHeads
    475						     ;
    476						     ; track = t1  /  nHeads		     (ax has track)
    477						     ; head  = t1 mod nHeads		     (dl has head)
    478						     ;
    479	0166  33 D2				     xor     dx, dx
    480	0168  F7 76 1A				     div     word ptr nHeads
    481
    482						     ; the following manipulations are necessary in order to
    483						     ; properly	place parameters into registers.
    484						     ; ch = cylinder number low	8 bits
    485						     ; cl = 7-6: cylinder high two bits
    486						     ;	    5-0: sector
    487	016B  8A F2				     mov     dh, dl		     ; save head into dh for bios
    488	016D  D0 CC				     ror     ah, 1		     ; move track high bits into
    489	016F  D0 CC				     ror     ah, 1		     ; bits 7-6	(assumes top = 0)
    490	0171  86 C4				     xchg    al, ah		     ; swap for	later
    491	0173  8A 56 18				     mov     dl, byte ptr sectPerTrack
    492	0176  2A D1				     sub     dl, cl
    493	0178  FE C1				     inc     cl			     ; sector offset from 1
    494	017A  0B C8				     or	     cx, ax		     ; merge cylinder into sector
    495	017C  8A C2				     mov     al, dl		     ; al has #	of sectors left
Turbo Assembler	 Version 3.1	    04/11/13 12:54:48	    Page 10
boot.ASM



    496
    497						     ; Calculate how many sectors can be transfered in this read
    498						     ; due to dma boundary conditions.
    499	017E  52				     push    dx
    500
    501	017F  8B F7				     mov     si, di		     ; temp register save
    502						     ; this computes remaining bytes because of	modulo 65536
    503						     ; nature of dma boundary condition
    504	0181  8B C3				     mov     ax, bx		     ; get offset pointer
    505	0183  F7 D8				     neg     ax			     ; and convert to bytes
    506	0185  74 0B				     jz	     ax_min_1		     ; started at seg:0, skip ahead
    507
    508	0187  33 D2				     xor     dx, dx		     ; convert to sectors
    509	0189  F7 76 0B				     div     word ptr bytesPerSector
    510
    511	018C  3B C7				     cmp     ax, di		     ; check remainder vs. asked
    512	018E  72 02				     jb	     ax_min_1		     ; less, skip ahead
    513	0190  8B F0				     mov     si, ax		     ; transfer	only what we can
    514
    515	0192  5A		     ax_min_1:	     pop     dx
    516
    517						     ; Check that request sectors do not exceed	track boundary
    518	0193  8B 76 18				     mov     si, sectPerTrack
    519	0196  46				     inc     si
    520	0197  8B C1				     mov     ax, cx		     ; get the sector/cyl byte
    521	0199  25 003F				     and     ax, 03fh		     ; and mask	out sector
    522	019C  2B F0				     sub     si, ax		     ; si has how many we can read
    523	019E  8B C7				     mov     ax, di
    524	01A0  3B F7				     cmp     si, di		     ; see if asked <= available
    525	01A2  7D 02				     jge     ax_min_2
    526	01A4  8B C6				     mov     ax, si		     ; get what	can be xfered
    527
    528	01A6  BE 0005		     ax_min_2:	     mov     si, RETRYCOUNT
    529	01A9  B4 02				     mov     ah, 2
    530	01AB  8A 56 24				     mov     dl, drive
    531
    532	01AE  50		     retry:	     push    ax
    533	01AF  CD 13				     int     13h
    534	01B1  58				     pop     ax
    535	01B2  73 10				     jnc     read_ok
    536	01B4  50				     push    ax
    537	01B5  33 C0				     xor     ax, ax	     ; reset the drive
    538	01B7  CD 13				     int     13h
    539	01B9  58				     pop     ax
    540	01BA  4E				     dec     si
    541	01BB  75 F1				     jnz     retry
    542	01BD  F9				     stc
    543	01BE  58				     pop     ax
    544	01BF  5A				     pop     dx
    545	01C0  5E				     pop     si
    546	01C1  C3				     ret
    547
    548	01C2  EB 9B		     read_next_jmp:  jmp     short read_next
    549	01C4  32 E4		     read_ok:	     xor     ah, ah
    550	01C6  8B F0				     mov     si, ax		     ; AX = SI = number	of sectors read
Turbo Assembler	 Version 3.1	    04/11/13 12:54:48	    Page 11
boot.ASM



    551	01C8  F7 66 0B				     mul     word ptr bytesPerSector ; AX = number of bytes read
    552	01CB  03 D8				     add     bx, ax		     ; add number of bytes read	to BX
    553	01CD  73 07				     jnc     no_incr_es		     ; if overflow...
    554
    555	01CF  8C C0				     mov     ax, es
    556	01D1  80 C4 10				     add     ah, 10h		     ; ...add 1000h to ES
    557	01D4  8E C0				     mov     es, ax
    558
    559	01D6  58		     no_incr_es:     pop     ax
    560	01D7  5A				     pop     dx			     ; DX:AX = last sector number
    561
    562	01D8  03 C6				     add     ax, si
    563	01DA  83 D2 00				     adc     dx, 0		     ; DX:AX = next sector to read
    564	01DD  2B FE				     sub     di, si		     ; if there	is anything left to read,
    565	01DF  7F E1				     jg	     read_next_jmp	     ; continue
    566
    567	01E1  F8				     clc
    568	01E2  5E				     pop     si
    569	01E3  C3				     ret
    570	01E4			     readDisk	     endp
    571
    572	01E4  42 6F 6F 74 20 65	72+  errmsg	     db	     "Boot error"
    573	      72 6F 72
    574	      =000A		     ERRMSGLEN	     equ     $ - errmsg
    575
    576
    577	01EE  49 50 4C 20 20 20	20+  filename	     db	     "IPL     SYS"
    578	      20 53 59 53
    579
    580						     org     BASE+01feh
    581	01FE  AA55		     sign	     dw	     0aa55h
    582
    583	0200			     TEXT	     ENDS
    584						     end
Turbo Assembler	 Version 3.1	    04/11/13 12:54:48	    Page 12
Symbol Table




Symbol Name			  Type	 Value

??DATE				  Text	 "04/11/13"
??FILENAME			  Text	 "boot	  "
??TIME				  Text	 "12:54:48"
??VERSION			  Number 030A
@CPU				  Text	 0101H
@CURSEG				  Text	 TEXT
@FILENAME			  Text	 BOOT
@WORDSIZE			  Text	 2
AX_MIN_1			  Near	 TEXT:0192
AX_MIN_2			  Near	 TEXT:01A6
BASE				  Number 0000
BOOT_ERROR			  Near	 TEXT:0140
BOOT_SUCCESS			  Near	 TEXT:0156
BYTESPERSECTOR			  Text	 [bp+0bh]
DATA_START			  Text	 [bp-12]
DRIVE				  Text	 [bp+24h]
ENTRY				  Near	 TEXT:0000
ERRMSG				  Byte	 TEXT:01E4
ERRMSGLEN			  Number 000A
EXTBOOT				  Text	 [bp+26h]
FATBUF				  Number 4000
FATERROR			  Near	 TEXT:011B
FAT_12				  Near	 TEXT:00F1
FAT_16				  Near	 TEXT:0106
FAT_EVEN			  Near	 TEXT:00FE
FAT_START			  Text	 [bp-4]
FFDONE				  Near	 TEXT:00C4
FILENAME			  Byte	 TEXT:01EE
FILESYS				  Text	 [bp+36h]
FINISHED			  Near	 TEXT:0118
FIRST_HALF			  Near	 TEXT:0110
LOADSEG				  Number 2000
LOAD_SEG			  Word	 TEXT:003E
MID				  Text	 [bp+15h]
NEXT_CHAR			  Near	 TEXT:0147
NEXT_CLUST			  Near	 TEXT:00E2
NEXT_CLUSTER			  Near	 TEXT:0125
NEXT_ENTRY			  Near	 TEXT:00A9
NEXT_TEST			  Near	 TEXT:0116
NFATS				  Text	 [bp+10h]
NHEADS				  Text	 [bp+1ah]
NHIDDEN				  Text	 [bp+1ch]
NO_INCR_ES			  Near	 TEXT:01D6
NROOTDIR			  Text	 [bp+11h]
NSECTORHUGE			  Text	 [bp+20h]
NSECTORS			  Text	 [bp+13h]
OEM				  Text	 [bp+3]
READDISK			  Near	 TEXT:015E
READ_NEXT			  Near	 TEXT:015F
READ_NEXT_JMP			  Near	 TEXT:01C2
READ_OK				  Near	 TEXT:01C4
REAL_START			  Near	 TEXT:0040
Turbo Assembler	 Version 3.1	    04/11/13 12:54:48	    Page 13
Symbol Table



RESSECTORS			  Text	 [bp+0eh]
RETRY				  Near	 TEXT:01AE
RETRYCOUNT			  Number 0005
ROOT_DIR_START			  Text	 [bp-8]
SECTPERCLUSTER			  Text	 [bp+0dh]
SECTPERFAT			  Text	 [bp+16h]
SECTPERTRACK			  Text	 [bp+18h]
SIGN				  Word	 TEXT:01FE
TEMPBUF				  Text	 [bp+3eh]
VOLID				  Text	 [bp+27h]
VOLLABEL			  Text	 [bp+2bh]

Macro Name

FINDFILE
GETDRIVEPARMS
GETFATCHAIN
LOADFILE

Groups & Segments		  Bit Size Align  Combine Class

TEXT				  16  0200 Word	  Public  TEXT