Initial commit

1 files changed, 246 insertions, 0 deletions

diff --git a/boot.asm b/boot.asm
new file mode 100644
index 0000000..d6ddfa1
--- /dev/null
+++ b/boot.asm
@@ -0,0 +1,246 @@
+bits 16
+
+jmp start
+
+CR equ 0Dh
+LF equ 0Ah
+K_CS_ADDR equ 007eh
+
+start:
+	mov ax, 07c0h
+	mov ds, ax		; set data segment
+	mov ax, 07e0h
+	mov ss, ax		; set stack segment
+	mov sp, 2000h		; 8192k
+
+	push bp			; set up stack frame
+	mov bp, sp
+	sub sp, 2		; local storage
+
+	mov [drive0], dl	; save first detected drive
+
+	call cls		; clear screen
+
+	push 0			;
+	call setcursor		; set cursor position
+
+	push banner		;
+	call puts		; print version
+	add sp, 2		; clean up
+
+	push word [drive0]
+	call disk_reset
+	add sp, 2
+
+	xor cx, cx
+	mov ax, K_CS_ADDR
+	mov es, ax
+
+	push msg_loading
+	call puts
+	add sp, 2
+
+	mov bx, 0
+	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, 200h		; increment address by 512 bytes
+	inc di			; increment sector read count
+	cmp di, 16		; 8K (i'll make this smarter later)
+	jle .loader		; keep reading
+
+	push msg_done
+	call puts
+	add sp, 2
+
+	add sp, 2		; remove local storage
+	mov sp, bp
+	pop bp
+
+	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:
+	push bp
+	mov bp, sp
+	pusha
+
+	mov ah, 00h		; reset disk
+	mov dl, [bp + 4]	; disk number
+	int 13h			; BIOS disk service
+	jnc .success
+
+	push error_msg_disk_reset
+	call panic
+
+.success:
+	popa
+	mov sp, bp
+	pop bp
+	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
+
+	push dx
+	call disk_reset
+	add sp, 2
+
+	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
+
+
+cls:
+	push bp
+	mov bp, sp
+	pusha
+
+	mov ah, 07h		; BIOS - scroll down
+	mov al, 00h		; lines to scroll (0 == entire screen)
+	mov bx, 0700h		; color white/black
+				; & video page zero
+	mov cx, 0
+	mov dh, 24		; rows
+	mov dl, 79		; cols
+	int 10h			; BIOS video service
+	popa
+
+	mov sp, bp
+	pop bp
+	ret
+
+
+setcursor:
+	push bp
+	mov bp, sp
+	pusha
+
+	mov ah, 02h		; BIOS - set cursor position
+	mov bh, 0		; video page zero
+	mov dx, [bp + 4]	; address of new cursor value
+	int 10h			; BIOS video service
+
+	popa
+	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
+
+
+
+; 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
+msg_disk_reset: db "Drive reset successful.", CR, LF, 0
+msg_disk_read: db "Sector read successful.", 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
+
+; boot signature
+times 510-($-$$) db 0
+dw 0xAA55
+