From f10fa026cfc3171aa66595c73552a13d7b4a07b0 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Fri, 18 Dec 2020 18:29:26 +0000
Subject: [PATCH] Add support for floppy types with other geometry than 18/2/80

---
 Makefile         |  5 ++++-
 kernel/drive.asm | 16 +++++++++++-----
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index cd8dcda..4a9a74e 100644
--- a/Makefile
+++ b/Makefile
@@ -68,9 +68,12 @@ clean:
 	rm -f *.com *.bs *.0 *.lst *.img *.bin *.rom
 	rm -rf utils
 
-qemu-floppy: fd1440.img $(ROMS)
+qemu-floppy3: fd1440.img $(ROMS)
 	$(QEMU) $(QEMU_ARGS) -boot a -fda fd1440.img
 
+qemu-floppy5: fd360.img $(ROMS)
+	 $(QEMU) $(QEMU_ARGS) -boot a -fda fd360.img
+
 qemu-hdd: hdimage.img $(ROMS)
 	$(QEMU) $(QEMU_ARGS) -boot c -hda hdimage.img
 
diff --git a/kernel/drive.asm b/kernel/drive.asm
index b78b52c..4582af6 100644
--- a/kernel/drive.asm
+++ b/kernel/drive.asm
@@ -46,6 +46,9 @@ logdrv:		; dont do anything if drive already selected
 		mov [dsknum], dl
 		; save info for bios
 		mov [biosnum], dl
+		; set default geometry (1.44 MB floppy)
+		mov word [bpb+BPBNOS], 2
+		mov word [bpb+BPBSPT], 18
 		; load boot sector
 		xor ax, ax
 		xor dx, dx
@@ -61,12 +64,18 @@ logdrv:		; dont do anything if drive already selected
 		mov [bpb+BPBHS+2], ax
 .ret:		ret
 
-calchs:		mov bx, (18*2)
+calchs:		; put sectors per cylinder into bx
+		mov ax, [bpb+BPBSPT]
+		mul word [bpb+BPBNOS]
+		mov bx, ax
+		; but linear sector num into dx:ax
+		mov ax, [dskseek]
+		mov dx, [dskseek+2]
 		; dx:ax = linear count, bx = sectors / cylinder
 		div bx
 		xchg ax, dx
 		; dx = cylinder, ax = head * spt + sector
-		mov bl, 18
+		mov bl, [bpb+BPBSPT]
 		div byte bl
 		; dx = cylinder, al = head, ah = sector
 		xchg dl, dh
@@ -134,9 +143,6 @@ dirty:		or byte [dskflag], 1 ; dirty
 		; flush buffer if dirty
 flush:		test byte [dskflag], 1
 		jz .ret
-		; load sector number
-		mov ax, [dskseek]
-		mov dx, [dskseek+2]
 		; do the write
 		; TODO: error handling & retries
 		call calchs