From 8d67cdf201c6c1ce4f6a2528e4c591a07faad1ec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Sun, 4 Jul 2021 18:52:11 +0300
Subject: [PATCH] Always do disk reads one sector at a time

PCem emulating IBM PC 5150 seems to have a bug where int 0x13/2 will report
it read zero sectors regardless of how many sectors it actually read.
---
 bootsect.asm | 36 +++++++++++-------------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/bootsect.asm b/bootsect.asm
index 6847bd6..146d86b 100644
--- a/bootsect.asm
+++ b/bootsect.asm
@@ -282,35 +282,21 @@ loadsectors:
 			and al, 0xC0
 			or cl, al
 
-		; Copy number of sectors to still read to ax and cap at 127
-		pop ax
-		push ax
-		cmp al, 127
-		jbe .read
-		mov al, 127
+		mov ah, 2
+		mov al, 1
+		mov dl, [drivenumber]
+		int 0x13
+		; TODO: Handle reset & retry
+		jnc .noerror
+		.noerror:
 
-		.read:
-			mov ah, 2
-			mov dl, [drivenumber]
-			int 0x13
-
-		; Decrement cx by the number of sectors read
 		pop cx
-		xor ah, ah
-		sub cx, ax
+		pop ax
 
-		; Increment bx by the number of sectors read times 512
-		xor dx, dx
-		mov dh, al
-		shl dx, 1
-		add bx, dx
+		inc ax
+		add bx, 512
 
-		; Increment ax by the number of sectors read
-		pop dx
-		add ax, dx
-
-		test cx, cx
-		jnz .loop
+		loop .loop
 
 	pop dx
 	pop cx