From de098cb9f325e6bc3e0a1ff3fb94e942fa0e42c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Sun, 4 Jul 2021 19:12:59 +0300
Subject: [PATCH] Finish up the remaining TODOs in bootsect.asm

---
 bootsect.asm | 61 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 49 insertions(+), 12 deletions(-)

diff --git a/bootsect.asm b/bootsect.asm
index 146d86b..45a5ea9 100644
--- a/bootsect.asm
+++ b/bootsect.asm
@@ -121,8 +121,15 @@ search_root:
 		je .end
 
 		test byte [si + 11], 0x08 + 0x10
-		jz .isfile
+		jnz .skipentry
 
+		; Make sure the file has non-zero size
+		cmp word [si + 28], 0
+		jne .isfile
+		cmp word [si + 30], 0
+		jne .isfile
+
+	.skipentry:
 		add si, 32
 		jmp .entry
 
@@ -154,18 +161,12 @@ search_root:
 	.end:
 
 notfound:
-	; TODO: Better error messages
-	mov ax, 0x0e00 + '?'
-	int 0x10
-
-hang:
-	hlt
-	jmp hang
+	mov si, notfound_msg
+	jmp fatal_error
 
 found:
 	; SI points to 11 bytes after the start of the entry, so adjust all
 	; offsets
-	; TODO: Handle zero-length files
 	mov ax, [si - 11 + 26] ; First cluster
 	push ax
 
@@ -248,8 +249,13 @@ loadsectors:
 	push ax
 	push cx
 	push dx
+	push di
 
 	.loop:
+		mov di, 3 ; Retry thrice
+
+		.retry:
+
 		push ax
 		push cx
 
@@ -286,9 +292,9 @@ loadsectors:
 		mov al, 1
 		mov dl, [drivenumber]
 		int 0x13
+
 		; TODO: Handle reset & retry
-		jnc .noerror
-		.noerror:
+		jc .error
 
 		pop cx
 		pop ax
@@ -298,15 +304,46 @@ loadsectors:
 
 		loop .loop
 
+	pop di
 	pop dx
 	pop cx
 	pop ax
 	ret
 
-%include "hexprint.inc"
+	.error:
+		; Do we still have retries remaining?
+		mov si, diskerror_msg
+		test di, di
+		jz fatal_error ; No, fail
+		dec di
+
+		; Yes, reset disk
+		xor ah, ah
+		int 0x13
+
+		; Execute the loop again
+		pop cx
+		pop ax
+		jmp .retry
+
+fatal_error:
+	lodsb
+	test al, al
+	jz hang
+	mov ah, 0xe
+	int 0x10
+	jmp fatal_error
+
+hang:
+	hlt
+	jmp hang
+
 
 kernel_name: db "KERNEL  BIN"
 
+notfound_msg: db "Kernel not found", 0
+diskerror_msg: db "Disk error", 0
+
 times 510-($-$$) db 0
 db 0x55, 0xaa
 _end: