; 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
BS_OEMName db 'KOLIBRI ' ; db 8
BPB_BytsPerSec dw 512 ; bytes per sector
BPB_SecPerClus db 1 ; sectors per cluster
BPB_RsvdSecCnt dw 1 ; number of reserver sectors
BPB_NumFATs db 2 ; count of FAT data structures
BPB_RootEntCnt dw 224 ; count of 32-byte dir. entries (224*32 = 14 sectors)
BPB_TotSec16 dw 2880 ; count of sectors on the volume (2880 for 1.44 mbytes disk)
BPB_Media db 0f0h ; f0 - used for removable media
BPB_FATSz16 dw 9 ; count of sectors by one copy of FAT
BPB_SecPerTrk dw 18 ; sectors per track
BPB_NumHeads dw 2 ; number of heads
BPB_HiddSec dd 0 ; count of hidden sectors
BPB_TotSec32 dd 0 ; count of sectors on the volume (if > 65535)
BS_DrvNum db 0 ; int 13h drive number
BS_Reserved db 0 ; reserved
BS_BootSig db 29h ; Extended boot signature
BS_VolID dd 0 ; Volume serial number
BS_VolLab db 'KOLIBRI ' ; Volume label (db 11)
BS_FilSysType db 'FAT12 ' ; file system type (db 8)
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
; <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
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:
; <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
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 ?
; <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 ?
loader_block:
db 1
dw 0
dw write1st+boot_program
dw 0
; <\diamond>
times 0x1fe-$ db 00h
db 55h,0aah ;boot signature