; 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'
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
; reading root directory
; al=count root dir sectors !!!! 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
jmp $
; === KERNEL FOUND. LOADING... ===
found_kernel_file:
mov bp,[si+01ah] ; first cluster of kernel file
; <diamond>
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
mov ax,seg_read_kernel
mov es,ax
xor bx,bx ; es:bx = 1000h:0000h
; reading kernel file
loop_obtains_kernel_data:
call obtain_cluster ; read one cluster of file
mov ax,es
add ax,seg_inc_per_cluster ; << =32(1.44M) or 64(2.88) >>
mov es,ax ; add one cluster length to segment:offset
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:
shr ax,4
verify_end_sector:
cmp ax,0ff8h ; last cluster
jae execute_kernel
mov bp,ax
jmp loop_obtains_kernel_data
execute_kernel:
; <diamond>
mov ax,'KL'
push 0
pop ds
mov si,loader_block+boot_program
; </diamond>
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
; jc $ ; error
pop bx
writesec:
; convert cluster number to sector number
mov ax,bp ; data cluster to read
sub ax,2
;>> add ax,ax ; << only for 2.88M disks! >>
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 ax,0x201 ; ah=2 (read)
;>> ; al=1(1.44) or 2(2.88)
; read sector from disk
read_sector:
push ax bx cx dx
int 13h
jc $ ; error: stop here
pop dx cx bx ax
retn
;------------------------------------------
; converts abs. sector number (AX) to BIOS T:H:S
; Returns: {pre.track number = (AX / BPB_SecPerTrk)}
; ch - track number = pre.track number/2
; cl - sector number = (abs.sector%BPB_SecPerTrk)+1
; dh - head number = pre.track number%BPB_NumHeads
; dl - drive number (0 = a:)
conv_abs_to_THS:
mov cx,word [BPB_SecPerTrk+boot_program] ; << 18 or 36 >>
xor dx,dx
div cx
inc dx
mov cl, dl ; cl = sector number
xor dx, dx
shr ax, 1
rol dx, 1 ; dh = head number
mov ch, al ; ch = track number
retn
;------------------------------------------
loading db cr,lf,'Starting system ',00h
;error_message db 13,10
kernel_name db 'KERNEL MNT',00h
FirstRootDirSecNum dw 19 ; 1st sector of the root dir
RootDirSecs dw 14 ; << = 14(1.44M) or 15(2.88M) >>
data_start dw 33 ; << = 33(1.44M) or 34(2.88M) >>
; <diamond>
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 ? ; 1st cluster of kernel.mnt
loader_block:
db 1
dw 0
dw write1st+boot_program
dw 0
; <\diamond>
times 0x1fe-$ db 00h
db 55h,0aah ;boot signature