From de48157cb811c927d7a2af1be1ed15b162a320a2 Mon Sep 17 00:00:00 2001
From: John Tsiombikas <nuclear@member.fsf.org>
Date: Wed, 16 Nov 2022 22:03:03 +0200
Subject: [PATCH] now it should boot on an IBM PC correctly (tested on pcem)

---
 .gitignore    |    1 +
 Makefile      |   20 ++++++++++++++------
 boot/boot.asm |   16 ++++++++++++----
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/.gitignore b/.gitignore
index 77c7ebc..a3492c9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@
 dis1
 dis2
 *.log
+bootldr
diff --git a/Makefile b/Makefile
index 8e95cce..5c19343 100644
--- a/Makefile
+++ b/Makefile
@@ -1,9 +1,17 @@
-bin = boot.img
+disk_numsec = 720
+#disk_numsec = 2880
+
+bin = bootldr
+img = bootldr.img
 
 CC = ia16-elf-gcc
 LD = ia16-elf-ld
 
-CFLAGS = -march=i8088 -mtune=i8088
+CFLAGS = -march=i8088 -mtune=i8088 -DFLOPPY360
+
+$(img): $(bin)
+	dd if=/dev/zero of=$@ bs=512 count=$(disk_numsec)
+	dd if=$< of=$@ bs=512 conv=notrunc
 
 $(bin): boot/boot.o boot/boot2.o boot/main.o
 	$(LD) -T boot.ld -Map boot.map -o $@ $^
@@ -17,12 +25,12 @@ clean:
 
 
 .PHONY: run
-run: $(bin)
-	qemu-system-i386 -fda $(bin) -serial file:serial.log
+run: $(img)
+	qemu-system-i386 -fda $(img) -serial file:serial.log
 
 .PHONY: debug
-debug: $(bin)
-	qemu-system-i386 -fda $(bin) -serial file:serial.log -s -S
+debug: $(img)
+	qemu-system-i386 -fda $(img) -serial file:serial.log -s -S
 
 .PHONY: disasm
 disasm: $(bin)
diff --git a/boot/boot.asm b/boot/boot.asm
index 2b74db8..96506de 100644
--- a/boot/boot.asm
+++ b/boot/boot.asm
@@ -27,21 +27,29 @@ cur_cyl		equ 7b14h	; 2 bytes - current cylinder
 %%end:	popf
 %endmacro
 
+; 5.25" 360K floppy
+BPB_DISK_SECTORS	equ 720
+BPB_TRACK_SECTORS	equ 9
+BPB_MEDIA_TYPE		equ 0fdh
+; 3.5" 1.44M floppy
+;BPB_DISK_SECTORS	equ 2880
+;BPB_TRACK_SECTORS	equ 18
+;BPB_MEDIA_TYPE		equ 0f0h
 
 bios_param_block:
 	jmp start	; 2 bytes
 	nop		; 1 byte
 	; start of BPB at offset 3
-	db "BSPL 0.1"	; 03h: OEM ident, 8 bytes
+	db "86BOOT00"	; 03h: OEM ident, 8 bytes
 	dw 512		; 0bh: bytes per sector
 	db 1		; 0dh: sectors per cluster
 	dw 1		; 0eh: reserved sectors (including boot record)
 	db 2		; 10h: number of FATs
 	dw 224		; 11h: number of dir entries
-	dw 2880		; 13h: number of sectors in volume
-	db 0fh		; 15h: media descriptor type (f = 3.5" HD floppy)
+	dw BPB_DISK_SECTORS	; 13h: number of sectors in volume
+	db BPB_MEDIA_TYPE	; 15h: media descriptor type (f0 = 3.5" HD floppy)
 	dw 9		; 16h: number of sectors per FAT
-	dw 18		; 18h: number of sectors per track
+	dw BPB_TRACK_SECTORS	; 18h: number of sectors per track
 	dw 2		; 1ah: number of heads
 	dd 0		; 1ch: number of hidden sectors
 	dd 0		; 20h: high bits of sector count
-- 
1.7.10.4