rdos/kernel/drive.asm

section .bss

		; drive actually selected for I/O
dsknum:		resb 1
		; current sector number
dskseek:	resd 1

		; disk buffer for I/O operations
dskbuf:		resb 512

section .text

ret:		ret

		; select drive
		; IN	dl	drive number
dsksel:		cmp dl, 1
		jnc ret
		mov al, dl
		and al, 0x02
		ror dl, 1
		ror dl, 1
		cmp dl, byte [dsknum]
		je ret

		call dskrst

		int 3

		ret

dskrst:		call flush
		mov ax, 0xFFFF
		mov [dsknum], al
		mov [dskseek], ax
		mov [dskseek+2], ax
		ret

		; flush buffer if dirty
flush:		ret