From 400f2827256166598cef93663b1cd21543d15e6f Mon Sep 17 00:00:00 2001
From: shikhin <draumr.shikhin@gmail.com>
Date: Thu, 16 Mar 2023 16:12:22 +0530
Subject: [PATCH] Merge read/write to modify_sector

---
 ponydos.asm | 66 +++++++++++++++--------------------------------------
 1 file changed, 19 insertions(+), 47 deletions(-)

diff --git a/ponydos.asm b/ponydos.asm
index 1db5054..d1c7532 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -171,24 +171,31 @@ read_sectors:
 	push ax
 	push cx
 	push bx
+	push di
 
+	xor di, di
 	.loop:
-		call read_sector
+		call modify_sector
 		inc ax
 		add bx, 512
 		loop .loop
 
+	pop di
 	pop bx
 	pop cx
 	pop ax
 	ret
 
 ; in:
-;  ax = LBA of sector
-; out:
-;  cx, dx = appropriately set for int 0x13
-;  ax clobbered
-prepare_geometry:
+;  ax = LBA of first sector
+;;  bl = drive number, use [boot_disk] for now
+;  es:bx = output buffer
+;  di = 0x0100 for write, 0x0000 for read
+modify_sector:
+	push ax
+	push cx
+	push dx
+
 	mov cx, 18
 	div cx
 
@@ -206,21 +213,10 @@ prepare_geometry:
 
 	; dl = drive number
 	mov dl, [boot_disk]
-	ret
-
-; in:
-;  ax = LBA of first sector
-;;  bl = drive number, use [boot_disk] for now
-;  es:bx = output buffer
-read_sector:
-	push ax
-	push cx
-	push dx
-
-	call prepare_geometry
 
 	.retry:
-	mov ax, 0x0201 ; read one sector
+	mov ax, 0x0201 ; read/write one sector
+	add ax, di
 	int 0x13
 	jc .error
 
@@ -237,32 +233,6 @@ read_sector:
 		int 0x10
 		jmp .retry
 
-; in:
-;  ax = LBA of first sector
-;;  bl = drive number, use [boot_disk] for now
-;  es:bx = input buffer
-write_sector:
-	push ax
-	push cx
-	push dx
-
-	call prepare_geometry
-
-	.retry:
-	mov ax, 0x0301 ; write one sector
-	int 0x13
-	jc .error
-
-	pop dx
-	pop cx
-	pop ax
-	ret
-
-	.error:
-		xor ah, ah
-		int 0x10
-		jmp .retry
-
 ; ------------------------------------------------------------------
 ; Filesystem
 ; ------------------------------------------------------------------
@@ -290,7 +260,8 @@ open_file:
 	;mov ax, 1
 	mov al, 1
 	mov bx, DIRENTS
-	call read_sector
+	xor di, di
+	call modify_sector
 
 	mov ax, 2
 	mov di, bx
@@ -336,7 +307,8 @@ open_file:
 		push ax
 		mov ax, 1
 		;mov bx, DIRENTS
-		call write_sector
+		mov di, 0x0100 ; write
+		call modify_sector
 		pop ax
 		
 		;mov cx, 1