; FAT12 boot sector for Kolibri OS ; ; Copyright (C) Alex Nogueira Teixeira ; Copyright (C) Diamond ; Copyright (C) Dmitry Kartashov aka shurf ; ; Distributed under GPL, see file COPYING for details ; ; Version 1.0 lf equ 0ah cr equ 0dh pos_read_tmp equ 0700h ;position for temporary read boot_program equ 07c00h ;position for boot code seg_read_kernel equ 01000h ;segment to kernel read jmp start_program nop ; Boot Sector and BPB Structure include 'floppy1440.inc' ;include 'floppy2880.inc' ;include 'floppy1680.inc' ;include 'floppy1743.inc' start_program: xor ax,ax mov ss,ax mov sp,boot_program push ss pop ds ; print loading string mov si,loading+boot_program loop_loading: lodsb or al,al jz read_root_directory mov ah,0eh mov bx,7 int 10h jmp loop_loading read_root_directory: push ss pop es ; calculate some disk parameters ; - beginning sector of RootDir mov ax,word [BPB_FATSz16+boot_program] xor cx,cx mov cl,byte [BPB_NumFATs+boot_program] mul cx add ax,word [BPB_RsvdSecCnt+boot_program] mov word [FirstRootDirSecNum+boot_program],ax ; 19 mov si,ax ; - count of sectors in RootDir mov bx,word [BPB_BytsPerSec+boot_program] mov cl,5 ; divide ax by 32 shr bx,cl ; bx = directory entries per sector mov ax,word [BPB_RootEntCnt+boot_program] xor dx,dx div bx mov word [RootDirSecs+boot_program],ax ; 14 ; - data start add si,ax ; add beginning sector of RootDir and count sectors in RootDir mov word [data_start+boot_program],si ; 33 ; reading root directory ; al=count root dir sectrors !!!! TODO: al, max 255 sectors !!!! mov ah,2 ; read push ax mov ax,word [FirstRootDirSecNum+boot_program] call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector) pop ax mov bx,pos_read_tmp ; es:bx read buffer call read_sector mov si,bx ; read buffer address: es:si mov ax,[RootDirSecs+boot_program] mul word [BPB_BytsPerSec+boot_program] add ax,si ; AX = end of root dir. in buffer pos_read_tmp ; find kernel file in root directory loop_find_dir_entry: push si mov cx,11 mov di,kernel_name+boot_program rep cmpsb ; compare es:si and es:di, cx bytes long pop si je found_kernel_file add si,32 ; next dir. entry cmp si,ax ; end of directory jb loop_find_dir_entry file_error_message: mov si,error_message+boot_program loop_error_message: lodsb or al,al jz freeze_pc mov ah,0eh mov bx,7 int 10h jmp loop_error_message freeze_pc: jmp $ ; endless loop ; === KERNEL FOUND. LOADING... === found_kernel_file: mov bp,[si+01ah] ; first cluster of kernel file ; mov [cluster1st+boot_program],bp ; starting cluster of kernel file ; <\diamond> ; reading first FAT table mov ax,word [BPB_RsvdSecCnt+boot_program] ; begin first FAT abs sector number call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector) mov bx,pos_read_tmp ; es:bx read position mov ah,2 ; ah=2 (read) mov al, byte [BPB_FATSz16+boot_program] ; FAT size in sectors (TODO: max 255 sectors) call read_sector jc file_error_message ; read error mov ax,seg_read_kernel mov es,ax xor bx,bx ; es:bx = 1000h:0000h ; reading kernel file loop_obtains_kernel_data: ; read one cluster of file call obtain_cluster jc file_error_message ; read error ; add one cluster length to segment:offset push bx mov bx,es mov ax,word [BPB_BytsPerSec+boot_program] ;\ movsx cx,byte [BPB_SecPerClus+boot_program] ; | !!! TODO: !!! mul cx ; | out this from loop !!! shr ax,4 ;/ add bx,ax mov es,bx pop bx mov di,bp shr di,1 pushf add di,bp ; di = bp * 1.5 add di,pos_read_tmp mov ax,[di] ; read next entry from FAT-chain popf jc move_4_right and ax,0fffh jmp verify_end_sector move_4_right: mov cl,4 shr ax,cl verify_end_sector: cmp ax,0ff8h ; last cluster jae execute_kernel mov bp,ax jmp loop_obtains_kernel_data execute_kernel: ; mov ax,'KL' push 0 pop ds mov si,loader_block+boot_program ; push word seg_read_kernel push word 0 retf ; jmp far 1000:0000 ;------------------------------------------ ; loading cluster from file to es:bx obtain_cluster: ; bp - cluster number to read ; carry = 0 -> read OK ; carry = 1 -> read ERROR ; print one dot push bx mov ax,0e2eh ; ah=0eh (teletype), al='.' xor bh,bh int 10h pop bx writesec: ; convert cluster number to sector number mov ax,bp ; data cluster to read sub ax,2 xor dx,dx mov dl,byte [BPB_SecPerClus+boot_program] mul dx add ax,word [data_start+boot_program] call conv_abs_to_THS ; convert abs sector (AX) to BIOS T:H:S (track:head:sector) patchhere: mov ah,2 ; ah=2 (read) mov al,byte [BPB_SecPerClus+boot_program] ; al=(one cluster) call read_sector retn ;------------------------------------------ ;------------------------------------------ ; read sector from disk read_sector: push bp mov bp,20 ; try 20 times newread: dec bp jz file_error_message push ax bx cx dx int 13h pop dx cx bx ax jc newread pop bp retn ;------------------------------------------ ; convert abs. sector number (AX) to BIOS T:H:S ; sector number = (abs.sector%BPB_SecPerTrk)+1 ; pre.track number = (abs.sector/BPB_SecPerTrk) ; head number = pre.track number%BPB_NumHeads ; track number = pre.track number/BPB_NumHeads ; Return: cl - sector number ; ch - track number ; dl - drive number (0 = a:) ; dh - head number conv_abs_to_THS: push bx mov bx,word [BPB_SecPerTrk+boot_program] xor dx,dx div bx inc dx mov cl, dl ; cl = sector number mov bx,word [BPB_NumHeads+boot_program] xor dx,dx div bx ; !!!!!!! ax = track number, dx = head number mov ch,al ; ch=track number xchg dh,dl ; dh=head number mov dl,0 ; dl=0 (drive 0 (a:)) pop bx retn ;------------------------------------------ loading db cr,lf,'Starting system ',00h error_message db 13,10 kernel_name db 'KERNEL MNT ?',cr,lf,00h FirstRootDirSecNum dw ? RootDirSecs dw ? data_start dw ? ; write1st: push cs pop ds mov byte [patchhere+1+boot_program], 3 ; change ah=2 to ah=3 mov bp,[cluster1st+boot_program] push 1000h pop es xor bx,bx call writesec mov byte [patchhere+1+boot_program], 2 ; change back ah=3 to ah=2 retf cluster1st dw ? loader_block: db 1 dw 0 dw write1st+boot_program dw 0 ; <\diamond> times 0x1fe-$ db 00h db 55h,0aah ;boot signature