; ; File: ; boot.asm ; Description: ; DOS-C boot ; ; Copyright (c) 1997; ; Svante Frey ; All Rights Reserved ; ; This file is part of DOS-C. ; ; DOS-C is free software; you can redistribute it and/or ; modify it under the terms of the GNU General Public License ; as published by the Free Software Foundation; either version ; 2, or (at your option) any later version. ; ; DOS-C is distributed in the hope that it will be useful, but ; WITHOUT ANY WARRANTY; without even the implied warranty of ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See ; the GNU General Public License for more details. ; ; You should have received a copy of the GNU General Public ; License along with DOS-C; see the file COPYING. If not, ; write to the Free Software Foundation, 675 Mass Ave, ; Cambridge, MA 02139, USA. ; ; $Header$ ; ; Rev 1.5 10 Jan 1997 4:58:06 patv ; Corrected copyright ; ; Rev 1.4 10 Jan 1997 4:52:50 patv ; Re-written to support C drive and eliminate restrictions on IPL.SYS ; ; Rev 1.3 29 Aug 1996 13:06:50 patv ; Bug fixes for v0.91b ; ; Rev 1.2 01 Sep 1995 17:56:44 patv ; First GPL release. ; ; Rev 1.1 30 Jul 1995 20:37:38 patv ; Initialized stack before use. ; ; Rev 1.0 02 Jul 1995 10:57:52 patv ; Initial revision. ; .text BASE equ 0 org BASE Entry: jmp real_start ; bp is initialized to 7c00h oem equ [bp+3] bytesPerSector equ [bp+0bh] sectPerCluster equ [bp+0dh] resSectors equ [bp+0eh] nFats equ [bp+10h] nRootDir equ [bp+11h] nSectors equ [bp+13h] MID equ [bp+15h] sectPerFat equ [bp+16h] sectPerTrack equ [bp+18h] nHeads equ [bp+1ah] nHidden equ [bp+1ch] nSectorHuge equ [bp+20h] drive equ [bp+24h] extBoot equ [bp+26h] volid equ [bp+27h] vollabel equ [bp+2bh] filesys equ [bp+36h] LOADSEG equ 2000h FATBUF equ 4000h ; offset of temporary buffer for FAT ; chain RETRYCOUNT equ 5 ; number of retries on disk errors ; Some extra variables that are created on the stack frame fat_start equ [bp-4] ; first FAT sector root_dir_start equ [bp-8] ; first root directory sector data_start equ [bp-12] ; first data sector ; ; Include macros for filesystem access ; include boot.inc ; ; ; org BASE+3eh tempbuf equ [bp+3eh] load_seg dw LOADSEG real_start: cli cld mov ax, cs mov ss, ax ; initialize stack mov bp, 7c00h lea sp, [bp-20h] sti mov es, ax mov ds, ax mov drive, dl ; BIOS passes drive number in DL GETDRIVEPARMS FINDFILE ; locate file in root directory jc boot_error ; fail if not found GETFATCHAIN ; read FAT chain LOADFILE ; load file (jumps to boot_sucess if successful) boot_error: mov cx, ERRMSGLEN mov si, offset errmsg+7c00h next_char: lodsb ; print error message mov ah, 0eh xor bh, bh int 10h loop next_char xor ah, ah int 16h ; wait for keystroke int 19h ; invoke bootstrap loader boot_success: mov dl, drive db 0eah ; far jump to LOADSEG:0000 dw 0 dw LOADSEG ; readDisk: Reads a number of sectors into memory. ; ; Call with: DX:AX = 32-bit DOS sector number ; DI = number of sectors to read ; ES:BX = destination buffer ; ES must be 64k aligned (1000h, 2000h etc). ; ; Returns: CF set on error ; ES:BX points one byte after the last byte read. readDisk proc push si read_next: push dx push ax ; ; translate sector number to BIOS parameters ; ; ; abs = sector offset in track ; + head * sectPerTrack offset in cylinder ; + track * sectPerTrack * nHeads offset in platter ; ; t1 = abs / sectPerTrack (ax has t1) ; sector = abs mod sectPerTrack (cx has sector) ; div word ptr sectPerTrack mov cx, dx ; ; t1 = head + track * nHeads ; ; track = t1 / nHeads (ax has track) ; head = t1 mod nHeads (dl has head) ; xor dx, dx div word ptr nHeads ; the following manipulations are necessary in order to ; properly place parameters into registers. ; ch = cylinder number low 8 bits ; cl = 7-6: cylinder high two bits ; 5-0: sector mov dh, dl ; save head into dh for bios ror ah, 1 ; move track high bits into ror ah, 1 ; bits 7-6 (assumes top = 0) xchg al, ah ; swap for later mov dl, byte ptr sectPerTrack sub dl, cl inc cl ; sector offset from 1 or cx, ax ; merge cylinder into sector mov al, dl ; al has # of sectors left ; Calculate how many sectors can be transfered in this read ; due to dma boundary conditions. push dx mov si, di ; temp register save ; this computes remaining bytes because of modulo 65536 ; nature of dma boundary condition mov ax, bx ; get offset pointer neg ax ; and convert to bytes jz ax_min_1 ; started at seg:0, skip ahead xor dx, dx ; convert to sectors div word ptr bytesPerSector cmp ax, di ; check remainder vs. asked jb ax_min_1 ; less, skip ahead mov si, ax ; transfer only what we can ax_min_1: pop dx ; Check that request sectors do not exceed track boundary mov si, sectPerTrack inc si mov ax, cx ; get the sector/cyl byte and ax, 03fh ; and mask out sector sub si, ax ; si has how many we can read mov ax, di cmp si, di ; see if asked <= available jge ax_min_2 mov ax, si ; get what can be xfered ax_min_2: mov si, RETRYCOUNT mov ah, 2 mov dl, drive retry: push ax int 13h pop ax jnc read_ok push ax xor ax, ax ; reset the drive int 13h pop ax dec si jnz retry stc pop ax pop dx pop si ret read_next_jmp: jmp short read_next read_ok: xor ah, ah mov si, ax ; AX = SI = number of sectors read mul word ptr bytesPerSector ; AX = number of bytes read add bx, ax ; add number of bytes read to BX jnc no_incr_es ; if overflow... mov ax, es add ah, 10h ; ...add 1000h to ES mov es, ax no_incr_es: pop ax pop dx ; DX:AX = last sector number add ax, si adc dx, 0 ; DX:AX = next sector to read sub di, si ; if there is anything left to read, jg read_next_jmp ; continue clc pop si ret readDisk endp errmsg db "Boot error" ERRMSGLEN equ $ - errmsg ;filename db "OSLDR BIN" filename db "KERNEL BIN" org BASE+01feh sign dw 0aa55h TEXT ENDS end