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|
bits 16
jmp start
CR equ 0Dh
LF equ 0Ah
K_CS_ADDR equ 0050h
; data
drive0: dw 0
banner: db "MINOS Bootloader", CR, LF, 0
; General messages
msg_loading: db "Loading", 0
msg_done: db "done!", CR, LF, 0
; Error messages
error_msg_panic: db "PANIC: ", 0
error_msg_disk_reset: db "Drive reset failed!", CR, LF, 0
error_msg_disk_read: db "Drive read failed!", CR, LF, 0
start:
cli
mov ax, 07C0h ; load bootstrap address
mov ds, ax ; set data segment
mov es, ax ; set extra segment
mov ax, stack_end ; load address of temp stack segment
mov ss, ax ; set stack end
mov cx, 01FCh
sub ax, cx
mov sp, ax ; set stack top before boot signature
sti
mov [drive0], dx ; save first detected drive
push banner ;
call puts ; print version
add sp, 2 ; clean up
push word [drive0]
call disk_reset
add sp, 2
push msg_loading
call puts
add sp, 2
; begin disk operations
xor cx, cx
mov ax, K_CS_ADDR
mov es, ax
mov bx, 0000h ; starting address (es:bx)
mov di, 2 ; start at sector
.loader:
mov al, 1 ; read one sector
mov cx, di ; track/cyl | sector number
mov dh, 0 ; head number
mov dl, [drive0] ; drive number
call disk_read
push '.'
call putc
add sp, 2
add bx, 0200h ; increment address by 512 bytes
inc di ; increment track read count
cmp di, 12h ; transfer 9K (512 * 18)
jle .loader ; keep reading
push msg_done
call puts
add sp, 2
mov dx, [drive0] ; the kernel will need the boot drive number
jmp K_CS_ADDR:0000h ; jump to kernel address
cli ; disable interrupts
jmp $ ; hang
panic:
; Hang system with supplied error message
push bp
mov bp, sp
push error_msg_panic ; i.e. 'PANIC:'
call puts
add sp, 2
push word [bp + 4] ; address of error string buffer
call puts ; print error
add sp, 2
cli ; disable interrupts
jmp $ ; hang (no return)
; stack is dead
disk_reset:
mov ah, 00h ; reset disk
; dl is drive number
int 13h ; BIOS disk service
jnc .success
push error_msg_disk_reset
call panic
.success:
ret
disk_read:
push bp
mov bp, sp
push di
mov di, 3 ; retry counter
.readloop:
push ax
push bx
push cx
mov ah, 02h ; BIOS - read disk sectors
int 13h ; BIOS disk service
jnc .success
call disk_reset
pop cx
pop bx
pop ax
dec di
jnz .readloop
push error_msg_disk_read
call panic
add sp, 2
.success:
pop di
mov sp, bp
pop bp
ret
putc:
; Write single character at cursor position
push bp
mov bp, sp
pusha
mov ah, 0eh ; BIOS - teletype
mov al, [bp + 4] ; character
mov bx, 0 ; video page zero
int 10h ; BIOS video service
popa
mov sp, bp
pop bp
ret
puts:
; Write string buffer at cursor position
push bp
mov bp, sp
pusha
mov si, [bp + 4] ; address of string buffer
mov bx, 0000h ;
mov ah, 0eh ; BIOS - teletype
.loop:
lodsb ; load byte at [si] into al
or al, 0 ; 0 | 0 = 0 (detect null terminator)
je .end
int 10h ; BIOS video service
jmp .loop
.end:
popa
mov sp, bp
pop bp
ret
stack_end: ; address of stack end
; boot signature
times 510-($-$$) db 0
dw 0xAA55
|
