From c75b323d31b75d4c2e9f03551a5ff872336da025 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Sat, 26 Dec 2020 17:44:48 +0000
Subject: [PATCH] Add support for hard disks

---
 boot/kernel.asm  |  6 +++-
 kernel/drive.asm | 87 ++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 82 insertions(+), 11 deletions(-)

diff --git a/boot/kernel.asm b/boot/kernel.asm
index c806402..4bca0fe 100644
--- a/boot/kernel.asm
+++ b/boot/kernel.asm
@@ -29,17 +29,21 @@ init:		cli
 		sub dl, (0x80-2)
 .k:		mov [defdrv], dl
 
-		call logdrv.force
+		call logdrv
 
 		xor ax, ax
 		xor dx, dx
 		call maprd
 
 		inc word [dskbuf+0x82]
+		push word [dskbuf+0x82]
 
 		call dirty
 		call flush
 
+		call printf
+		db "Current run: ",2,0x0A,0x0D,0
+
 hlt:		hlt
 		jmp hlt
 
diff --git a/kernel/drive.asm b/kernel/drive.asm
index 7ad68cd..9e09c75 100644
--- a/kernel/drive.asm
+++ b/kernel/drive.asm
@@ -65,15 +65,33 @@ int13:		; debug output
 		stc
 		ret
 
-		; restore DPT to default values if possible
-		; IN	dl	bios drive number
-rstdpt:		mov ah, 8
+		; get drive parameters
+		; read BIOS int13h/AH=8 values
+		; DPT data gets copied over our dpt
+		; CHS data gets inserted into our bpb
+getprm:		mov ah, 8
+		mov dl, [biosnum]
 		call int13
-		jc .ret
-		mov ax, es
+		; bail out if error
+		jc .nodpt
+		; get and store sector number
+		and cx, 0x3F
+		mov word [bpb+BPBSPT], cx
+		; get and store number of heads
+		xchg dl, dh
+		and dx, 0xFF
+		inc dx
+		mov [bpb+BPBNOS], dx
+		; print geometry
+		push dx
+		push cx
+		call printf
+		db "getprm: ",2," sectors, ",2," heads",0x0A,0x0D,0
+		; test if DPT ptr is non-zero
+.nochs:		mov ax, es
 		or ax, di
 		test ax, ax
-		jz .ret
+		jz .nodpt
 		; DS:SI = ES:DI
 		mov ax, es
 		mov ds, ax
@@ -85,9 +103,10 @@ rstdpt:		mov ah, 8
 		; do the copy
 		mov cx, 11
 		rep movsb
-.ret:		; restore DS to 0
+.nodpt:		; restore segment registers
 		xor ax, ax
 		mov ds, ax
+		mov es, ax
 		ret
 
 		; log in drive
@@ -95,7 +114,7 @@ rstdpt:		mov ah, 8
 		; IN	dl	drive number
 logdrv:		; dont do anything if drive already selected
 		cmp dl, [dsknum]
-		je .ret
+		je logfdd.ret
 		; clear out current contents
 		push dx
 		call flush
@@ -106,10 +125,14 @@ logdrv:		; dont do anything if drive already selected
 		pop dx
 		; set current drive number
 		mov [dsknum], dl
-		; save info for bios
+		; fork off if hdd
+		cmp dl, 2
+		jnc loghdd
+
+logfdd:		; save info for bios
 		mov [biosnum], dl
 		; reset dpt to defaults
-		call rstdpt
+		call getprm
 		; set default geometry (1.44 MB floppy)
 		mov word [bpb+BPBNOS], 2
 		mov word [bpb+BPBSPT], 18
@@ -132,6 +155,50 @@ logdrv:		; dont do anything if drive already selected
 		mov [bpb+BPBHS+2], ax
 .ret:		ret
 
+loghdd:		sub dl, 2
+		cmp dl, 4
+		jnc logerr
+		push dx
+		mov byte [biosnum], 0x80
+		; get chs data (needed or we cant load vbr)
+		call getprm
+		; read mbr
+		xor ax, ax
+		xor dx, dx
+		call mapabs
+		; get partition number
+		pop bx
+		xor bh, bh
+		mov cl, 4
+		sal bx, cl
+		; bail out if no partition
+		cmp byte [dskbuf+0x1be+bx+4], 0
+		je logerr
+		; load partition offset
+		mov ax, [dskbuf+0x1be+bx+8]
+		mov dx, [dskbuf+0x1be+bx+8+2]
+		; save to to stack
+		push dx
+		push ax
+		; load vbr
+		call mapabs
+		; copy bpb
+		mov si, dskbuf+BPBOFF
+		mov di, bpb
+		mov cx, BPBSIZ4
+		rep movsb
+		; fix CHS data
+		call getprm
+		; fix partition offset
+		pop ax
+		pop dx
+		mov [bpb+BPBHS], ax
+		mov [bpb+BPBHS+2], dx
+		ret
+
+logerr:		stc
+		ret
+
 mapclu:		; counting from begin of cluster area
 		mov bx, [bpb+BPBRDE]
 		mov cl, 4