; sector.S -- boot program named:  HIPBOOT.SYS;             from any MSDOS floppy diskette;; Copyright 2001-2002 John Coffman.; All rights reserved.;; Licensed under the terms contained in the file 'COPYING' in the LILO; source directory.;#define DEBUG 0		/* enables loading .EXE for codeview debugging */#define OPTION 1	/* enables fast directory search exit */#define LARGE 0		/* enables loading code >32K */#define TESTFAT 0	/* enables testing for FAT12/FAT16 */#define SYSSEG 0x1000  	/* load at a fixed address SYSSEG:0000 */;;directory_entry         			block	0dir_filename:		.blkb	8dir_filename_ext:	.blkb	3dir_attribute:		.blkb	1dir_Reserved:		.blkb	10dir_time_updated:	.blkw	1dir_date_updated:	.blkw	1dir_cluster:		.blkw	1dir_file_size:		.blkw	2dir_entry_size:			endbbase    equ     0x7C00buffer  equ     0x0500          ;scratch disk buffer;contAddr  equ   SS:[bp-4]      ;dword     DO NOT MOVE;dataBase  equ   SS:[bp-8]       ;dword    DO NOT MOVE;FATshift  equ   SS:[bp-9]      ; byte ;diskNumber  equ SS:[bp-10]      ; byte    DO NOT MOVE;dirBase equ     SS:[bp-14]       ;dword;nDirSec equ     SS:[bp-16]      ;word;FATsector equ   SS:[bp-18]      ;word;FATnibbles  equ SS:[bp-20]      ;wordstacksize	equ	20			block	-stacksizeFATnibbles:	.blkw	1FATsector:	.blkw	1nDirSec:	.blkw	1dirBase:	.blkw	2diskNumber:	.blkb	1	; DO NOT MOVEFATshift:	.blkb	1dataBase:	.blkw	2	; DO NOT MOVEcontAddr:	.blkw	2	; DO NOT MOVEstack:	/* this had better be zero */		.blkb	3	; jump instruction		.blkb	8	; system ID stringsecSiz:		.blkw	1	; bytes_per_sectorsecPerCl:	.blkb	1	; sectors_per_clusterFATbase:	.blkw	1	; reserved_sectorsnFATs:		.blkb	1	; FAT_copiesnDirEnt:	.blkw	1	; directory_entriestotSec:		.blkw	1	; total_sectorsmedia:		.blkb	1	; media_descriptorsecPerFAT:	.blkw	1	; sectors_per_FATnSEC:		.blkw	1	; sectors_per_tracknSides:		.blkw	1	; heads_per_cylinderhidSec:		.blkw	2	; hidden_sectors		.blkb	22fs_id:		.blkb	8	; filesystem_id			endb.globl _main			org	0; jump instruction_main:			jmp	beginning			nopsystem_id_string:	.ascii	"DISKBOOT"	; 8 charsmsdos_boot_data:bytes_per_sector:	dw	512sectors_per_cluster:	db	1reserved_sectors:	dw	1FAT_copies:		db	2directory_entries:	dw	224       ; 112 & 224 are typicaltotal_sectors:		dw	2880media_descriptor:	db	0xf0      ; 0f9H, 0f0h, 0fAh, etc.sectors_per_FAT:	dw	9sectors_per_track:	dw	18heads_per_cylinder:	dw	2hidden_sectors:		dd	0       ; always zero for floppiestotal_sectors_2:	dd      0       ; actual value if 'total_sectors' is zeroBPB_rsvd:		dw      0       ; reservedvol_id_marker:		db      0x29    ; marker? for volume IDserial_number:		dd      0       ; volume unique ID numbervolume_label:		.ascii	"NO NAME    "	; 11 charsfilesystem_id:		.ascii	"FAT12   "	;  8 charsbeginning:        xor     ax,ax        mov     bp,#base         ;origin at 7C00#if DEBUG        xor     dl,dl        mov     ax,ss#endif        cli        mov     ss,ax        lea     sp,(bp-stacksize)        sti        cld        mov     es,ax           ;both at zero        mov     ds,ax#if DEBUG        xor     ax,ax#endif        mov     diskNumber(bp),dl   ;save disk number        int     0x13             ;reset the disk system        jc      errornoError:        mov     ax,#0x0403        ;shift=4, nibbles=3 -- FAT12fat12   equ     *-2#if TESTFAT        cmp     fs_id+4(bp),'6'        jne     isFAT12        mov     ax,#0004        ;shift=0, nibbles=4 -- FAT16isFAT12:#endif        mov     FATshift(bp),ah     ;set shift count        cbw        mov     FATnibbles(bp),ax   ;set number of nibbles per FAT index entry        mov     al,nFATs(bp)        ;number of FATs;       cbw        mul     secPerFAT(bp)       ;* sectors per FAT        add     ax,FATbase(bp)      ;+ FAT base        adc     dx,#0            ; SI = 0        mov     dirBase(bp),ax        mov     dirBase+2(bp),dx    ;save directory base        mov     dataBase(bp),ax        mov     dataBase+2(bp),dx   ;still forming Data base         mov     ax,#dir_entry_size        mul     nDirEnt(bp)        mov     bx,secSiz(bp)        add     ax,bx                   dec     ax        div     bx              ;get base of data#if DEBUG        add     bx,bx#endif#if SYSSEG        mov     contAddr(bp),ss            ; SS = 0        mov     contAddr+2(bp),#SYSSEG      ; begin at SYSSEG:0000#else        add     bx,#base        mov     contAddr(bp),bx     ;save continuation address        mov     contAddr+2(bp),es#endif        mov     nDirSec(bp),ax      ;save no. of Directory sectors        add     dataBase(bp),ax        adc     word ptr dataBase+2(bp),#0           ; SI = 0; scan the directory for the required bootstrap file        mov     ax,dirBase(bp)      ; starting disk block in DX:AX        mov     dx,dirBase+2(bp)dirscan:        mov     bx,#buffer        ; ES:BX points to buffer        call    ReadSector        mov     di,bx        mov     bx,secSiz(bp)dirscan1:                call    S21tofind: .ascii	"HIPBOOT SYS"error:        call    write        db      13,10,10	.ascii	'Non-SYSTEM disk or disk error'        db      13,10	.ascii	'Press any key to re-boot ...'	db	0done:        xor     ax,ax        int     0x16             ;wait for keypress        int     0x19             ;re-bootS21:    pop     si        push    di        mov     cx,#11           ;name length        rep     	 seg cs	  cmpsb    ;byte ptr CS:[si],ES:[di]        pop     di        je      hipboot#if OPTION        cmp     byte ptr (di),#0        je      endOfDirectory#endif        lea     di,dir_entry_size(di)        sub     bx,#dir_entry_size        jg      dirscan1        inc     ax        dec     word ptr nDirSec(bp)        jnz     dirscanendOfDirectory:error2:        jmp     errorReadSector:        push    dx              ;save registers        push    cx        push    ax                add     ax,hidSec(bp)       ;+ Hidden Sectors        adc     dx,hidSec+2(bp)     ;        xchg    ax,dx        push    dx              ;AX=dividend-hi, DX=dividend-low        cwd        div     nSEC(bp)            ;DX=remainder, AX=quo-hi                pop     cx        xchg    ax,cx           ;CX=quo-hi, DX:AX=dividend-low        div     nSEC(bp)            ;remainder is sector number, zero based        inc     dx              ;DX=sector#, CX:AX=quotient        push    dx              ;save sector number        mov     dx,cx           ;DX:AX=quotient        div     nSides(bp)          ;DX = side, AX = Cyl No.        mov     cl,#6        shl     ah,cl           ;AH is hi-bits of cyl no.        pop     cx              ;restore sector number        or      cl,ah        mov     ch,al        mov     dh,dl        mov     dl,diskNumber(bp)retry:        mov     ax,#0x0201        ;BIOS read 1 sector        int     0x13#if DEBUG        jnc     readcont        xor     ax,ax        int     0x13        jmp     retryreadcont:#endiferror3:        jc      error2        pop     ax        pop     cx        pop     dx        rethipboot:        mov     cx,dir_cluster(di)        mov     word ptr FATsector(bp),#-1    ;no FAT sector present        les     bx,contAddr(bp)     ;get continue addressnextCluster:        call    readCluster        push    es        push    bx        mov     ax,FATnibbles(bp)   ;get number of nibbles in a FAT entry        mul     cx              ;DX:AX is nibble index        shr     dx,1        rcr     ax,1            ;DX:AX is byte index, CF=odd/even        pushf                   ;save CF        mov     si,secSiz(bp)       ;sector size to SI        div     si              ;AX is rel. sector, DX is byte offset        mov     di,dx           ;DI is byte offset        push    ds        pop     es        mov     bx,#buffer        call    ForceFatSector  ;AX is rel. FATsector to force        mov     dl,(bx+di)   ;get low byte        dec     si        inc     di        and     di,si           ;mask DI byte offset        jnz     sameFATsec        inc     ax        call    ForceFatSectorsameFATsec:        mov     dh,(bx+di)        popf                    ;restore shift flag        mov     cl,FATshift(bp)        jc      shiftIt        shl     dx,clshiftIt:        shr     dx,cl        mov     si,#-1        shr     si,cl           ;si is EOF        and     si,#-8		;0xFFF8        mov     cx,dx           ;CX is next cluster        pop     bx        pop     es        cmp     cx,si        jb      nextCluster        mov     ch,media(bp)        ;pass on media descriptor        lea     sp,diskNumber(bp)        pop     dx        pop     bx              ;low order start of data        pop     ax              ;high order start of data#if DEBUG        jmp     done#endif        retfreadCluster:        push    cx        mov     al,secPerCl(bp)     ;sectors per cluster        cbw        xchg    ax,cx           ;AX=cluster #,  CX=# sectors per cluster        dec     ax        dec     ax              ;base it at 0, instead of 2        mul     cx        add     ax,dataBase(bp)     ;offset onto disk        adc     dx,dataBase+2(bp)readClus1:        call    ReadSector      ;read a sector        add     bx,secSiz(bp)       ;update address#if LARGE        jnc     readClus2        mov     si,es           ;get segment register        add     si,#0x1000        ;REAL mode increment        mov     es,si           ;update segment register#else        jc      error3          ;segment overflow#endifreadClus2:        inc     ax              ;update sector number        jnz     readClus3        inc     dxreadClus3:        loop    readClus1        pop     cx        retForceFatSector:        push    dx        cmp     ax,FATsector(bp)        je      gotFATsector        mov     FATsector(bp),ax        add     ax,FATbase(bp)        xor     dx,dx        call    ReadSectorgotFATsector:        pop     dx        retwrite:        pop     si              ;get character string pointerwrite1:	seg cs        lodsb   ;byte ptr CS:[si]        test    al,al        jz      return        mov     ah,#0x0e        mov     bx,#7        int     0x10        jmp     write1return:        jmp     si	org	510	dw	0xAA55		; BOOT_SIGNATUREendup:theend: