[haiku-development] mbrstub.asm for boot menu
- From: R Nikolaev <rhaiku@xxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Thu, 14 May 2009 12:50:32 -0700 (PDT)
;
; Haiku-OS Boot
; MBR Stub - The stub is used if boot menu is unnecessary
; Must be compiled as DOS COM
; Copyright (C) 2008 Ruslan Nikolaev
;
.MODEL TINY
.CODE
.486
ORG 7C00h ; BIOS loads the sector to this address
disk_addr_packet EQU 7A00h
drive_params EQU 7B00h
; Entry point
start:
cli ; disable interrupts
xor dh,dh ; DH = 0 (clear higher word of DH just in case)
jmp 0h,mbrstub_init
; Partition sector (offset 0x8)
partition_sector DD 0,0
; Initialization
mbrstub_init:
xor ax,ax
mov ds,ax ; DS = 0h
mov ah,30h
mov ss,ax ; SS = 3000h
mov es,ax ; ES = 3000h
mov sp,7000h ; SP = 7000h
sti ; enable interrupts
mov cx,100h ; copy 2x256 bytes
mov si,7C00h ; SI = 7C00h
mov di,si ; DI = 7C00h
cld
rep movsw
mov ds,ax ; set DS = 3000h
jmp 3000h, mbrstub_main
; Program
mbrstub_main:
test dx,80h
jnz @F
mov dx,80h ; fix BIOS bug
@@: mov ax,4100h ; EDD installation check
mov bx,55AAh
push dx
int 13h
pop dx ; keep DX
cmp bx,0AA55h
jne edd_error
mov si,drive_params
mov WORD PTR [si],1Ah ; size of the buffer
mov WORD PTR [si+18h],100h ; put 512-bytes as a sector size (just in case)
mov WORD PTR [si+2h],0h ; flags (reset just in case)
mov ax,4800h ; EDD get drive parameters
push dx
int 13h
mov ax,[si+18h]
mov bx,ax ; keep sector size here
add ax,511 ; always read at least 512 bytes
xor dx,dx
div bx ; AX = number of blocks to transfer
pop dx ; restore DX
mov si,disk_addr_packet
mov WORD PTR [si],10h ; size of the packet + reserved byte
mov [si+2h],ax ; put number of blocks to transfer
xor ax,ax
mov [si+6h],ax ; transfer buffer (SEGMENT) = 0h
mov WORD PTR [si+4h],7C00h ; transfer buffer (OFFSET) = 7C00h
mov eax,[partition_sector]
mov [si+8h],eax
mov eax,[partition_sector+4]
mov [si+0Ch],eax
mov ax,4200h ; EDD read
push dx
int 13h
pop dx
test ah,ah
jnz read_error
; Jump to the partition loader
cli ; disable interrupts
xor ax,ax
mov es,ax ; ES = 0
mov ds,ax ; DS = 0
mov ss,ax ; SS = 0
sti ; enable interrupts
jmp 0h,7C00h
; EDD error
edd_error:
mov si,OFFSET edd_error_string
mov cx,edd_error_string_len
jmp print_error
edd_error_string DB "ERROR: EDD does not work."
edd_error_string_len EQU $ - edd_error_string
; Read error
read_error:
mov si,OFFSET read_error_string
mov cx,edd_error_string_len
jmp print_error
read_error_string DB "ERROR: boot fault."
read_error_string_len EQU $ - read_error_string
; Error (SI: string, CX: length)
print_error:
cld ; DF = 0 (do it all the time; just in case)
lodsb
mov ah,0Eh ; print in teletype mode
mov bx,0003h ; bh: page, bl: attribute (light grey)
int 10h
loop print_error
@@: jmp @B ; halt the system
; ---------------------------
; Should not exceed 256 bytes
; ---------------------------
; Reserved area
ORG start+1B8h ; adjust PC
DB 70 DUP(?) ; MBR table
DW 55AAh ; MBR signature
END start
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