From 8e87cf0f759d58e9dc7a426ef93a7c6570b5fb1d Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Thu, 17 Sep 2020 05:57:46 +0000
Subject: [PATCH] Load kernel from reserved sectors in fatfs

---
 Makefile        | 25 +++++++++++--------------
 boot/kernel.asm | 27 ++++++++++++++++++++++++---
 boot/mbr.asm    |  2 +-
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/Makefile b/Makefile
index 8acbb1d..b6027c6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,5 @@
-FLOPPY = 1440
-
 PROGRAMS = hello.com
-DISTFILES = $(PROGRAMS) kernel.bs
+DISTFILES = $(PROGRAMS)
 ROMS =
 
 QEMU_ARCH = $(shell uname -m)
@@ -9,7 +7,7 @@ QEMU = qemu-system-$(QEMU_ARCH)
 QEMU_ARGS = $(addprefix --option-rom ,$(ROMS))
 
 NASM = nasm
-NASM_ARGS = -s -Ilib -DFLOPPY=$(FLOPPY)
+NASM_ARGS = -s -Ilib
 
 EMUL = utils/emul
 
@@ -28,7 +26,7 @@ endif
 
 .PHONY: default bootstrap clean qemu-rom qemu-floppy qemu-pxe
 
-default: fdimage.img
+default: fd1440.img
 
 # Host utils
 utils/%: %.c
@@ -59,14 +57,13 @@ fat6.bs: boot/fat.asm
 %.rom: rom/%.asm utils/fix-rom
 	$(NASM) $(NASM_ARGS) -o $@ $< && utils/fix-rom $@
 
-fdimage.img: fat1.bs $(DISTFILES)
-	mformat -C -i $@ -f $(FLOPPY) -B fat1.bs ::
-	mmd -i $@ ::rdos
-	mcopy -i $@ $(DISTFILES) ::rdos
-	mattrib -i $@ +s ::rdos ::rdos/kernel.bs
+fd%.img: kernel.bs $(DISTFILES)
+	mformat -C -i $@ -f $* -R 8 -B kernel.bs ::
+	dd if=kernel.bs conv=notrunc bs=512 skip=1 seek=1 of=$@
+	mcopy -i $@ $(DISTFILES) ::
 
-hdimage.img: mbr.bs fdimage.img
-	cat mbr.bs fdimage.img >$@
+hdimage.img: mbr.bs fd1440.img
+	cat mbr.bs fd1440 >$@
 
 part.img: fatc.bs $(DISTFILES)
 	dd if=/dev/zero bs=1024 count=33k of=$@
@@ -82,8 +79,8 @@ clean:
 	rm -f *.com *.bs *.0 *.lst *.img *.bin *.rom
 	rm -rf utils
 
-qemu-floppy: fdimage.img $(ROMS)
-	$(QEMU) $(QEMU_ARGS) -boot a -fda fdimage.img
+qemu-floppy: fd1440.img $(ROMS)
+	$(QEMU) $(QEMU_ARGS) -boot a -fda fd1440.img
 
 qemu-hdd: hdd.img $(ROMS)
 	$(QEMU) $(QEMU_ARGS) -boot c -hda hdd.img
diff --git a/boot/kernel.asm b/boot/kernel.asm
index 1b37760..b742457 100644
--- a/boot/kernel.asm
+++ b/boot/kernel.asm
@@ -7,11 +7,12 @@
 		; kernel stack size in words
 %define		stacksize 512
 
-		jmp init
+		jmp near init
 
-		times ( 0x0B - ($-$$) ) db " "
+		db "LOVELAIN"
 
-		times bpb_size db 0
+		; mformat writes stuff until 0x3E
+params:		times ( 0x3E - ($-$$) ) nop
 
 init:		cli
 		xor ax, ax
@@ -20,11 +21,31 @@ init:		cli
 		mov ss, ax
 		mov sp, ( stack+stacksize )
 
+		mov ax, [params+bpb.sectoroffset]
+		mov dx, [params+bpb.sectoroffset+2]
+
+		mov ax, 0x0201
+		mov cx, 0x0002
+		mov dh, 0
+		mov bx, 0x7E00
+		int 0x13
+
+		mov ax, [0x7E00]
+		mov cx, [0x7E02]
+		mov dx, [0x7E04]
+
 		int 3
 
 hlt:		hlt
 		jmp hlt
 
+		times (0x1FE - ($-$$)) db 0
+		dw 0xAA55
+
+		db "rdos kernel"
+
+end:		align 512
+
 section .bss
 
 stack:		resb stacksize
diff --git a/boot/mbr.asm b/boot/mbr.asm
index 6655e48..c6b7bce 100644
--- a/boot/mbr.asm
+++ b/boot/mbr.asm
@@ -131,7 +131,7 @@ part1:	db 0x80
 	db 0x01
 	db 0xFF, 0xFF, 0xFF
 	dd 1
-	dd (FLOPPY * 2)
+	dd (1440 * 2)
 
 	times (0x1FE - ($-$$)) db 0