From c70f388548d65f03537c21fed76551c85f78df33 Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Tue, 17 Sep 2019 22:41:39 +0000
Subject: [PATCH] Get MBR ready, add hdimage target

---
 Makefile        | 15 ++++++++---
 boot/fatvbr.asm |  4 +++
 boot/mbr.asm    | 67 ++++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 79 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index a4f3f67..c2c2836 100644
--- a/Makefile
+++ b/Makefile
@@ -29,18 +29,27 @@ kernel.com: kernel/*.asm lib/*.inc
 debug.rom: debug/*.asm lib/*.inc
 	nasm -s -o $@ -I lib -I debug debug/main.asm && scripts/fix-rom.sh $@
 
-floppy.bs: boot/fatvbr.asm
+boot/floppy.bs: boot/fatvbr.asm
 	nasm -s -DCMDLINE='"KERNEL.COM"' -o $@ $<
 
+boot/mbr.bs: boot/mbr.asm
+	nasm -s -DFLOPPY=$(FLOPPY) -o $@ $<
+
 programs/%.com: programs/%.asm
 	nasm -s -I lib -o $@ $<
 
-fdimage.img: floppy.bs $(DISTFILES)
-	mformat -C -i $@ -f $(FLOPPY) -B floppy.bs ::
+fdimage.img: boot/floppy.bs $(DISTFILES)
+	mformat -C -i $@ -f $(FLOPPY) -B boot/floppy.bs ::
 	mcopy -i $@ $(DISTFILES) ::
 
+hdimage.img: boot/mbr.bs fdimage.img
+	cat boot/mbr.bs fdimage.img >$@
+
 clean:
 	rm -f *.com *.bin *.rom *.img *.log *.bs *.lst programs/*.com
 
 qemu-floppy: fdimage.img $(DEBUGROM)
 	$(QEMU) $(QEMU_ARGS) -boot c -fda fdimage.img
+
+qemu-hdd: hdimage.img $(DEBUGROM)
+	$(QEMU) $(QEMU_ARGS) -boot c -hda hdimage.img
diff --git a/boot/fatvbr.asm b/boot/fatvbr.asm
index a75338e..321454f 100644
--- a/boot/fatvbr.asm
+++ b/boot/fatvbr.asm
@@ -151,6 +151,10 @@ load_sectors:
   push cx
   push dx
 
+  ; add partition offset (required for HDD)
+  add ax, [fdc.po]
+  adc dx, [fdc.po+2]
+
   ; calculate CHS data
   div word [cs:fdc.spt]    ; ax:temp     = (lba / spt)
   inc dx                   ; dx:sector   = (lba % spt) + 1
diff --git a/boot/mbr.asm b/boot/mbr.asm
index 48109f0..c7cb2e2 100644
--- a/boot/mbr.asm
+++ b/boot/mbr.asm
@@ -2,6 +2,11 @@
 %define self      0x00600 ; 1 sector
 %define prog      0x07C00 ; 1 sector
 
+; FDC fields in VBR
+%define spt       (prog + 0x18)
+%define nos       (prog + 0x1A)
+%define po        (prog + 0x1C)
+
 org self
 cpu 8086
 
@@ -26,15 +31,69 @@ init:
   jmp 0:main
 
 main:
-  mov bp, 0x0035
-  mov WORD [dap.blocknum], 1
+  mov bp, 0x3335
+  mov si, part1
+  mov cx, 4
+.loop:
+  test BYTE [si], 0x80
+  jnz loadpart
+  add si, 0x10
+  loop .loop
+  jmp error
+
+loadpart:
+  ; transfer starting address into DAP
+  push si
+  add si, 0x08
+  mov di, dap.blocknum
+  movsw
+  movsw
+  pop si
+
+  ; load sector
+  push si
   mov si, dap
+  mov bp, 0x3336
   mov ah, 0x42
   stc
   int 0x13
   jc error
-  mov cx, [dap.blocknum]
-  int3
+  pop si
+
+  cmp BYTE [si+4], 0x01
+  jne jump
+
+adjust:
+  push dx
+
+  mov bp, 0x3337
+  mov ah, 0x08
+  stc
+  int 0x13
+  jc error
+
+  ; update sectors per track
+  xor ax, ax
+  mov al, cl
+  mov [spt], ax
+
+  ; update number of sides
+  xor ax, ax
+  mov al, dh
+  mov [nos], ax
+
+  ; update partition offset
+  push si
+  add si, 0x08
+  mov di, po
+  movsw
+  movsw
+  pop si
+
+  pop dx
+
+jump:
+  jmp 0:prog
 
 error:
   mov ax, bp