rdos/kernel/fcb.asm

section .text

		; set default drive for current process
		; IN	dl	drive number
setdd:		push ds
		mov ds, [cs:curpsp]
		mov [PSPDD], dl
		pop ds
		ret

		; get default drive for current process
		; OUT	al	drive number
getdd:		push ds
		mov ds, [cs:curpsp]
		mov al, [PSPDD]
		pop ds
		ret

		; auto-complete drive field in fcb
		; IN	ds:dx	far ptr FCB
		; OUT	si	copy of dx
fixfcb:		mov si, dx
		cmp byte [si], 0
		jne .ret
		call getdd
		inc dl
		mov byte [si], dl
.ret:		mov dx, si
		ret

		; Load root directory entry
		; IN	ax	number of directory entry
lddir:		push ax
		mov cl, 4
		shr ax, cl
		xor dx, dx
		call maprd
		; get si to point to entry
		pop si
		mov cl, 5
		shl si, cl
		and si, 0x1FF
		add si, dskbuf
		ret

		; find next file
fnfile:		mov ax, [es:bx+FCBDEN]
		inc word [es:bx+FCBDEN]
		; bail out if we are at end of dir
		cmp ax, [bpb+BPBRDE]
		jnc .err
		; load entry and first byte
		push bx
		call lddir
		pop bx
		; next if hidden, dir or vol label
		test byte [si+0x0B], 0xDA
		jnz fnfile
		; bail out if end of dir
		mov al, [si]
		cmp al, 0
		je .err
		; next if deleted entry
		cmp al, 0xE5
		je fnfile
		clc
		ret
.err:		stc
		ret

		; Open file using FCB
		; IN	DS:DX	far ptr to FCB
open:		call fixfcb
		int 3
		ret