From fbab63261611f235ce8e01569aff4dd137f5bf36 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Fri, 19 Mar 2021 18:50:50 +0000
Subject: [PATCH] Implement file open

---
 kernel/fcb.asm | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/kernel/fcb.asm b/kernel/fcb.asm
index f2ce2f6..61bc2f5 100644
--- a/kernel/fcb.asm
+++ b/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