Implement file open

kernel/fcb.asm

@@ -1,9 +1,15 @@
 ; FCB layout
-; 1 byte drive (0=default, 1=A:, 2=B:, ...)
-; 8.3 filename
-; 8.3 filename for rename
 
-FCBSIZ	equ 30
+struc FCB
+
+FCBDRV	resb 1 ; BYTE drive (0=default, 1=A:, 2=B:, ...)
+FCBFN	resb 11 ; 11 BYTES filename
+FCBCLUS	resw 1 ; DWORD current cluster
+FCBRN	resb 1 ; BYTE record in cluster
+
+endstruc
+
+FCBSIZ	equ FCB_size
 
 section .data
 
@@ -136,11 +142,13 @@ fndnxt	mov bp, sp
 	; copy over drive byte
 	movsb
 	; copy filename
+	push ds
 	mov ax, cs
 	mov ds, ax
 	mov si, bx
 	mov cx, 11
 	rep movsb
+	pop ds
 	; done!
 	xor ax, ax
 	ret
@@ -149,5 +157,12 @@ fndnxt	mov bp, sp
 .ret:	sbb al, al
 	ret
 
-open:
-	ret
+open	call fndfst
+	test al, al
+	jnz .ret
+	; read start cluster
+	mov ax, [cs:bx+26]
+	mov [ds:bx+FCBCLUS], ax
+	; reset record number
+	mov byte [ds:bx+FCBRN], 0
+.ret	ret