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;; boot.stage1.asm
[org 0x7c00]
[bits 16]
%include "boot.common.asm"
%define LOAD_ADDRESS 0x7C00
%define STAGE2_ADDRESS 0x7E00
%define RELOCATE_ADDRESS 0x0600
%define SECTOR_SIZE 512
%define OFFSET_RELOC (RELOCATE_ADDRESS - LOAD_ADDRESS)
%define STAGE2_SECTORS 8
global _start
_start:
jmp 0x0000:.setup_segments
.setup_segments:
;; Disable interrupts
cli
;; Setup segment registers
xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax
mov gs, ax
mov sp, LOAD_ADDRESS ; Adjust stack
;; Save disk
mov [drive], dl ; Get drive ID from BIOS
sti
mov si, LOAD_ADDRESS
mov di, RELOCATE_ADDRESS
mov cx, SECTOR_SIZE
cld
rep movsdb
jmp 0x0000:(next)
_read_disk_real_mode:
.start:
cmp cx, 127
jbe .good_size
pusha
mov cx, 127
call _read_disk_real_mode
popa
add eax, 127
add dx, 127*512/16
sub cx, 127
jmp .start
.good_size:
mov [DAP.LBA_lower], ax
mov [DAP.num_sectors], cx
mov [DAP.buf_segment], dx
mov [DAP.buf_offset], bx
mov dl, [disk]
mov si, DAP
mov ah, 0x42
int 0x13
jc .disk_read_err
ret
.disk_read_err:
mov si, disk_read_err_msg
call _print_string
.halt: hlt
jmp .halt
_print_string:
pusha
mov ah, 0x0e
mov bh, 0x00
.print_loop:
lodsb
test al, al
je .print_return
int 0x10
jmp .print_loop
.print_return:
popa
ret
_end:
hlt
jmp _end
drive: db 0
disk_read_err_msg: db "Failed to read disk", 13, 10, 0
disk_read_success_msg: db "Read the disk successfully", 13, 10, 0
boot_msg: db "Booting", 13, 10, 0
DAP:
db 0x10
db 0
.num_sectors: dw 127
.buf_offset: dw 0x0
.buf_segment: dw 0x0
.LBA_lower: dd 0x0
.LBA_upper: dd 0x0
;; Padding and magic number
times 510 - ($ - $$) db 0
dw 0xaa55
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