1 [bits 16]
2 [cpu 286]
3 
4 
5 NUM_SECTORS equ 16
6 
7 section .boot exec write
8 global _start
9 extern _entry
10 _start:
11 	mov byte [bootdrv], dl
12 
13 	; reset boot drive
14 	xor ah, ah
15 	mov dl, byte [bootdrv]
16 	int 0x13
17 	jc error
18 
19 .loop:
20 	lea bp, [ldstr]
21 	call puts
22 
23 	; read sectors
24 	stc
25 	mov ah, 0x02
26 	mov al, NUM_SECTORS
27 	xor ch, ch
28 	mov cl, 2
29 	xor dh, dh
30 	mov dl, byte [bootdrv]
31 	mov bx, 0x1000
32 	mov es, bx
33 	xor bx, bx
34 	int 0x13
35 	jnc .ok
36 
37 	; reset boot drive again
38 	stc
39 	xor ah, ah
40 	mov dl, byte [bootdrv]
41 	int 0x13
42 	jnc error
43 
44 	dec byte [tries]
45 	jnz .loop
46 	jmp error
47 
48 .ok:
49 	push word [bootdrv]
50 	mov ax, 0x1000
51 	mov ds, ax
52 	mov es, ax
53 	jmp 0x1000:_entry
54 
55 error:
56 	lea bp, [errstr]
57 	; fallthrough
58 
59 puts:
60 	mov al, byte [bp]
61 	inc bp
62 	test al, al
63 	jz .ret
64 
65 	mov ah, 0x0E
66 	xor bx, bx
67 	int 0x10
68 	jmp puts
69 
70 .ret:
71 	ret
72 
73 ldstr:
74 	db "Loading kernel...", 13, 10, 0
75 
76 errstr:
77 	db "Error", 13, 10, 0
78 
79 bootdrv:
80 	db 0
81 
82 tries:
83 	db 5
84 
85 times 510 - ($ - $$) db 0
86 dw 0xAA55