From 1cbd918b56c86c7d9df751a67e7b23ffdac71ae9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Mon, 28 Mar 2022 16:53:55 +0300
Subject: [PATCH] Proof of concept 720k disk support

---
 Makefile |  2 +-
 boot.asm | 12 ++++++------
 io.asm   | 15 ++++++++++++---
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 7f602e3..b766c3f 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@ DOSBOX=dosbox -conf dosbox-build.conf -exit
 
 ordos.img: BOOT.BIN IO.SYS ORDOS.SYS COMMAND.COM debug.com edlin.com exe2bin.exe link.exe masm.exe
 	rm -f ordos.img
-	mkfs.fat -C $@ -M 0xff 320
+	mkfs.fat -C $@ 720
 	rw -I 0x7c00 -i BOOT.BIN -o $@ -c 512
 	mcopy -i $@ IO.SYS ::
 	mcopy -i $@ ORDOS.SYS ::
diff --git a/boot.asm b/boot.asm
index 1864551..a395488 100644
--- a/boot.asm
+++ b/boot.asm
@@ -17,12 +17,12 @@ jmp code
 	dw 512 ; Bytes per sector
 	db 2 ; Sectors per cluster
 	dw 1 ; Reserved sectors
-	db 2 ; FATs
+fats db 2 ; FATs
 	dw 112 ; Root directory entries
-	dw 2*320 ; Total sectors
-	db 0ffh ; Media descriptor
-	dw 1 ; Sectors per fat
-sectorspertrack dw 8
+	dw 2*720 ; Total sectors
+	db 0f9h ; Media descriptor
+sectorsperfat dw 3 ; Sectors per fat
+sectorspertrack dw 9
 heads dw 2
 	dd 0 ; Hidden sectors
 	dd 0 ; Total sectors (large)
@@ -40,7 +40,7 @@ code:
 	mov drivenumber, dl
 
 	; TODO: Check we actually have the OS
-	mov ax, 10
+	mov ax, 14
 	mov bx, 600h
 	mov cx, 17 ; This is what PC-DOS 1.10's full size ends up at
 	call loadsectors
diff --git a/io.asm b/io.asm
index ddf09f5..2d49e5e 100644
--- a/io.asm
+++ b/io.asm
@@ -1,7 +1,7 @@
 ; SPDX-License-Identifier: MIT
 ; Copyright (c) 2021 Juhani 'nortti' Krekelä.
 
-debug equ 0
+debug equ 1
 
 iosegment equ 60h
 dossegment equ iosegment + 1*1024/16 ; DOS starts 1KiB after IO system
@@ -558,14 +558,15 @@ code ends
 
 constants segment
 
-sectorspertrack dw 8 ; TODO: Don't hardcode
+sectorspertrack dw 9 ; TODO: Don't hardcode
 heads dw 2 ; TODO: Don't hardcode
 
 disks_table:
 	db 1 ; 1 drive, TODO: Don't hardcode
 
 	db 0 ; Physical drive 0
-	dw offset iogroup:parameters_320k
+	;dw offset iogroup:parameters_320k
+	dw offset iogroup:parameters_720k
 
 parameters_320k:
 	dw 512 ; Sector size in bytes
@@ -575,6 +576,14 @@ parameters_320k:
 	dw 112 ; Number of directory entries
 	dw 320*2 ; Number of sectors
 
+parameters_720k:
+	dw 512 ; Sector size in bytes
+	db 2 ; Sectors per cluster
+	dw 1 ; Number of reserved sectors
+	db 2 ; Number of FATs
+	dw 112 ; Number of directory entries
+	dw 720*2 ; Number of sectors
+
 doubleticks_per_hour dw 32772 ; 1800B0h / 2 / 24
 ticks_per_minute dw 1092 ; 1800B0h / 24 / 60
 ticks_per_second dw 18 ; 1800B0h / 24 / 60 / 60