From 9cd4c04c42224de3d0f7e4e9debe9a4716ea5c6d Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Tue, 15 Sep 2020 21:38:26 +0200
Subject: [PATCH] Make kernel and fat.bs use BPB struct

---
 Makefile     |  11 +-
 boot/fat.asm | 526 ++++++++++++++++++++++-----------------------------
 inc/bpb.asm  |  46 ++---
 3 files changed, 247 insertions(+), 336 deletions(-)

diff --git a/Makefile b/Makefile
index d83cba9..8acbb1d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-FLOPPY = 360
+FLOPPY = 1440
 
 PROGRAMS = hello.com
 DISTFILES = $(PROGRAMS) kernel.bs
@@ -55,15 +55,6 @@ fat4.bs: boot/fat.asm
 fat6.bs: boot/fat.asm
 	$(NASM) $(NASM_ARGS) -DFAT16 -DCHS -DLARGE -o $@ $<
 
-fatb.bs: boot/fat.asm
-	$(NASM) $(NASM_ARGS) -DFAT32 -DCHS -DLARGE -o $@ $<
-
-fatc.bs: boot/fat.asm
-	$(NASM) $(NASM_ARGS) -DFAT32 -DLBA -DLARGE -o $@ $<
-
-fate.bs: boot/fat.asm
-	$(NASM) $(NASM_ARGS) -DFAT16 -DLBA -DLARGE -o $@ $<
-
 # BIOS option roms
 %.rom: rom/%.asm utils/fix-rom
 	$(NASM) $(NASM_ARGS) -o $@ $< && utils/fix-rom $@
diff --git a/boot/fat.asm b/boot/fat.asm
index cdbe931..37228f4 100644
--- a/boot/fat.asm
+++ b/boot/fat.asm
@@ -1,338 +1,270 @@
-	; Bootsector for FAT32 filesystems
-	; Takes defines:
-	; 	FAT12	FAT has 1.5 bytes per entry
-	; 	FAT16	FAT has WORD per entry
-	; 	FAT32	FAT has DWORD per entry
-	; 	CHS	uses int13h/AH=02h
-	; 	LARGE	requires 32 bit sector numbers
-	; 	LBA	uses int13h/AH=42h
-	cpu 8086
+		; Bootsector for FAT12/FAT16 filesystems
+		; Takes defines:
+		; 	FAT12	FAT has 1.5 bytes per entry
+		; 	FAT16	FAT has WORD per entry
+		cpu 8086
 
-	org 0x0800
-	jmp short init
-	nop
+		org 0x0800
+		jmp short init
+		nop
 
-	%include "inc/bpb.asm"
+		%include "inc/bpb.asm"
 
-bpb:	equ 0x080B
+		times ( 0x0B - ($-$$) ) db 0
 
-	; Area for BPB
-	%ifdef FAT32
-	times ( 0x5A - ($-$$) ) db 0
-	%else
-	times ( 0x3E - ($-$$) ) db 0
-	%endif
+params:		times bpb_size db 0
 
-init:	xor ax, ax
-	mov ss, ax
-	mov sp, 0x7C00
+		; Area for BPB
+		times ( 0x3E - ($-$$) ) db 0
 
-	; save potential partition table entry
-	push ds
-	push si
+init:		xor ax, ax
+		mov ss, ax
+		mov sp, 0x7C00
 
-	mov ds, ax
-	mov es, ax
+		; save potential partition table entry
+		push ds
+		push si
 
-	mov si, 0x7C00
-	mov di, 0x0800
-	mov cx, 0x0100
-	rep movsw
-	jmp 0x0:main
+		mov ds, ax
+		mov es, ax
 
-	%include "inc/booterr.asm"
+		mov si, 0x7C00
+		mov di, 0x0800
+		mov cx, 0x0100
+		rep movsw
+		jmp 0x0:main
 
-	; offsets relative to FS
-readd:	; add offset of cluster data area to DX:AX
-	push cx
-	mov di, [bp+bpb_rde]
-	mov cl, 4
-	shr di, cl ; 32 bytes per entry
-	add ax, di
-	adc dx, 0
-	pop cx
-readr:	; add offset to rootdir to DX:AX (FAT12/FAT16 only)
-	push cx
-	xor ch, ch
-	mov cl, byte [bp+bpb_fn]
-fatlp:
-	%ifdef FAT32
-	add ax, [bp+bpb7_lsf]
-	adc dx, [bp+bpb7_lsf+2]
-	%else
-	add ax, [bp+bpb_sf]
-	adc dx, 0
-	%endif
-	loop fatlp
-	pop cx
-readf:	; add offset to FAT table to DX:AX
-	add ax, word [bp+bpb_rsc]
-	adc dx, 0
-readp:	; read sector DX:AX from partition
-	add ax, word [bp+bpb_po]
-	adc dx, word [bp+bpb_po+2]
-	jnc ($+5)
-	call errcll
+		%include "inc/booterr.asm"
 
-	%ifdef LBA
-read_:	; read sector DX:AX from disk
-	; this uses the EBIOS extensions
-	; qword sector number DX:AX
-	push cs
-	push cs
-	push dx
-	push ax
+		; offsets relative to FS
+readd:		; add offset of cluster data area to DX:AX
+		push cx
+		mov di, [bp+bpb.direntries]
+		mov cl, 4
+		shr di, cl ; 32 bytes per entry
+		add ax, di
+		adc dx, 0
+		pop cx
+readr:		; add offset to rootdir to DX:AX (FAT12/FAT16 only)
+		push cx
+		xor ch, ch
+		mov cl, byte [bp+bpb.fatnumber]
+fatlp:		add ax, [bp+bpb.fatsectors]
+		adc dx, 0
+		loop fatlp
+		pop cx
+readf:		; add offset to FAT table to DX:AX
+		add ax, word [bp+bpb.reservedsects]
+		adc dx, 0
+readp:		; read sector DX:AX from partition
+		add ax, word [bp+bpb.sectoroffset]
+		adc dx, word [bp+bpb.sectoroffset+2]
+		jnc ($+5)
+		call errcll
 
-	; dword target buffer: BX:0
-	push bx
-	push cs
+read_:		; read sector DX:AX from disk
+		; uses basic CHS disk IO
+		; this cant reliable read over track boundaries
+		; so we read each single sector in loop over CX
+chslp:		push ax
+		push cx
+		push dx
+		push bx
 
-	; word sector number
-	push cx
+		; calculate CHS data
+		div word [bp+bpb.tracksectors] ; ax:temp     = (lba / spt)
+		inc dx                         ; dx:sector   = (lba % spt) + 1
+		mov cl, dl ; sector number
+		xor dx, dx
+		div word [bp+bpb.heads]    ; ax:cylinder = (tmp / heads)
+		                           ; dx:head     = (tmp % heads)
+		mov ch, al ; cylinder number
+		mov dh, dl ; head number
+		mov dl, [bp+bpb.drivenum] ; drive number
 
-	; size & passing
-	mov di, 0x10
-	push di
+		; set up read buffer
+		mov es, bx
+		xor bx, bx
 
-	mov si, sp
-	mov ah, 0x42
-	mov dl, [bp+bpb7_dn]
-	stc
-	int 0x13
-	jnc ($+5)
-	call errcll
+		; call bios
+		mov ax, 0x0201
+		int 0x13
+		jnc ($+5)
+		call errcll
 
-	add sp, di
+		pop bx
+		pop dx
+		pop cx
+		pop ax
 
-	ret
-	%endif
+		; increment sector num + write offset
+		add ax, 1
+		adc dx, 0
+		add bx, 0x20
+		; loop on CX
+		loop chslp
+		ret
 
-	%ifdef CHS
-read_:	; read sector DX:AX from disk
-	; uses basic CHS disk IO
-	; this cant reliable read over track boundaries
-	; so we read each single sector in loop over CX
-chslp:	push ax
-	push cx
-	push dx
-	push bx
+next:		; Advances DX:AX to next FAT entry
+		push ax
+		push bx
+		; shift 2 left for dword-sized FAT entries
+		; shift 9 right for sector size
+		mov cl, 7
+shftl:		clc
+		rcr dx, 1
+		rcr ax, 1
+		loop shftl
 
-	; calculate CHS data
-	div word [bp+bpb_spt]    ; ax:temp     = (lba / spt)
-	inc dx                   ; dx:sector   = (lba % spt) + 1
-	mov cl, dl ; sector number
-	xor dx, dx
-	div word [bp+bpb_nos]    ; ax:cylinder = (tmp / heads)
-	                         ; dx:head     = (tmp % heads)
-	mov ch, al ; cylinder number
-	mov dh, dl ; head number
-	mov dl, [bp+bpb7_dn] ; drive number
+		mov bx, 0xA0
+		%ifdef FAT12
+		; FAT item might span over two sectors
+		mov cx, 2
+		%else
+		mov cx, 1
+		%endif
+		call readf
 
-	; set up read buffer
-	mov es, bx
-	xor bx, bx
+		pop bx
 
-	; call bios
-	mov ax, 0x0201
-	int 0x13
-	jnc ($+5)
-	call errcll
+		; get address of cluster within sector
+		pop si
+		%ifdef FAT12
+		push si
+		; times 1.5
+		mov ax, si
+		shr ax, 1
+		add si, ax
+		add si, buf
+		lodsw
+		pop si
+		test si, 1
+		jz .odd
+.even:		mov cl, 4
+		shr ax, cl
+		jmp .done
+.odd:		and ax, 0x0FFF
+.done:		xor dx, dx
+		%endif
 
-	pop bx
-	pop dx
-	pop cx
-	pop ax
+		%ifdef FAT16
+		; double
+	        sal si, 1
+		; make sure its within sector range
+		and si, 0x1FF
+		add si, buf
+		; load word
+		lodsw
+		xor dx, dx
+		%endif
 
-	; increment sector num + write offset
-	add ax, 1
-	adc dx, 0
-	add bx, 0x20
-	; loop on CX
-	loop chslp
-	ret
-	%endif
+		ret
 
-next:	; Advances DX:AX to next FAT entry
-	push ax
-	push bx
-	; shift 2 left for dword-sized FAT entries
-	; shift 9 right for sector size
-	mov cl, 7
-shftl:	clc
-	rcr dx, 1
-	rcr ax, 1
-	loop shftl
+		; reads current cluster into [dest]
+readc:		; load cluster number
+		push ax
+		push dx
 
-	mov bx, 0xA0
-	%ifdef FAT12
-	; FAT item might span over two sectors
-	mov cx, 2
-	%else
-	mov cx, 1
-	%endif
-	call readf
+		; subtract the two dummy entries from FAT start
+		sub ax, 2
+		sbb dx, 0
 
-	pop bx
-
-	; get address of cluster within sector
-	pop si
-	%ifdef FAT12
-	push si
-	; times 1.5
-	mov ax, si
-	shr ax, 1
-	add si, ax
-	add si, buf
-	lodsw
-	pop si
-	test si, 1
-	jz .odd
-.even:	mov cl, 4
-	shr ax, cl
-	jmp .done
-.odd:	and ax, 0x0FFF
-.done:	xor dx, dx
-	%endif
-
-	%ifdef FAT16
-	; double
-        sal si, 1
-	; make sure its within sector range
-	and si, 0x1FF
-	add si, buf
-	; load word
-	lodsw
-	xor dx, dx
-	%endif
-
-	%ifdef FAT32
-	; multiply with 4
-	sal si, 1
-	sal si, 1
-	; make sure its within sector range
-	and si, 0x1FF
-	add si, buf
-	; load dword
-	lodsw
-	mov dx, [si]
-	%endif
-
-	ret
-
-	; reads current cluster into [dest]
-readc:	; load cluster number
-	push ax
-	push dx
-
-	; subtract the two dummy entries from FAT start
-	sub ax, 2
-	sbb dx, 0
-
-	; convert cluster number to sector number
-	; this is some cheapo multiplication with 2^n
-	mov cl, [bp+bpb_sc]
-l02:	shr cl, 1
-	jz l02e
-	clc
-        rcl ax, 1
-        rcl dx, 1
-	jmp l02
+		; convert cluster number to sector number
+		; this is some cheapo multiplication with 2^n
+		mov cl, [bp+bpb.clustersects]
+l02:		shr cl, 1
+		jz l02e
+		clc
+        	rcl ax, 1
+        	rcl dx, 1
+		jmp l02
 l02e:
-	; dx:ax is now sector num in data area
-	mov cx, [bp+bpb_sc]
-	xor ch, ch
+		; dx:ax is now sector num in data area
+		mov cx, [bp+bpb.clustersects]
+		xor ch, ch
 
-	call readd
+		call readd
 
-	xchg di, cx
-	mov cl, 5
-	sal di, cl
-	add bx, di
+		xchg di, cx
+		mov cl, 5
+		sal di, cl
+		add bx, di
 
-	pop dx
-	pop ax
+		pop dx
+		pop ax
 
-	ret
+		ret
 
-	; Load root directory
-loadr:
-	%ifdef FAT32
-	mov ax, 2
-	xor dx, dx
-	jmp load
-	%else
-	mov ax, [bp+bpb_rde]
-	mov cl, 4
-	shr ax, cl
-	mov cx, ax
-	xor ax, ax
-	xor dx, dx
-	mov bx, 0x07C0
-	jmp readr
-	%endif
+		; Load root directory
+loadr:		mov ax, [bp+bpb.direntries]
+		mov cl, 4
+		shr ax, cl
+		mov cx, ax
+		xor ax, ax
+		xor dx, dx
+		mov bx, 0x07C0
+		jmp readr
 
-	; Load file identified by fsattr
-	; Directory data is expected at 0x07C00
-loadf:	mov si, (0x7C00-0x20)
-sloop:	add si, 0x20
-	; check if entry is valid
-	mov al, [si]
-	; unallocated direntry
-	test al, al
-	jnz ($+5)
-	call errcll
-	; deleted files
-	cmp al, 0xE2
-	je sloop
-	; check attr
-	mov al, [si+11]
-	and al, 0x5C
-	cmp al, ah
-	jne sloop
-	mov ax, [si+0x1A]
-	mov dx, [si+0x14]
+		; Load file identified by fsattr
+		; Directory data is expected at 0x07C00
+loadf:		mov si, (0x7C00-0x20)
+sloop:		add si, 0x20
+		; check if entry is valid
+		mov al, [si]
+		; unallocated direntry
+		test al, al
+		jnz ($+5)
+		call errcll
+		; deleted files
+		cmp al, 0xE2
+		je sloop
+		; check attr
+		mov al, [si+11]
+		and al, 0x5C
+		cmp al, ah
+		jne sloop
+		mov ax, [si+0x1A]
+		mov dx, [si+0x14]
 
-	; Load cluster chain DX:AX to 0x07C00
-load:	mov bx, 0x07C0
-lloop:	call readc
-	call next
-	%ifdef FAT12
-	cmp word ax, 0x0FF8
-	%endif
-	%ifdef FAT16
-	cmp word ax, 0xFFF8
-	%endif
-	%ifdef FAT32
-	cmp word dx, 0x0FFF
-	%endif
-	jc lloop
-	ret
+		; Load cluster chain DX:AX to 0x07C00
+load:		mov bx, 0x07C0
+lloop:		call readc
+		call next
+		%ifdef FAT12
+		cmp word ax, 0x0FF8
+		%endif
+		%ifdef FAT16
+		cmp word ax, 0xFFF8
+		%endif
+		jc lloop
+		ret
 
-main:	; Set up BP to point to BPB
-	; Relative addressing saves one instruction byte per access
-	mov bp, bpb
-	; Save DL contents
-	mov [bp+bpb7_dn], dl
+main:		; Set up BP to point to BPB
+		; Relative addressing saves one instruction byte per access
+		mov bp, params
+		; Save DL contents
+		mov [bp+bpb.drivenum], dl
 
-	; load root directory
-	call loadr
-	; search for first system directory
-	mov ah, 0x14
-	call loadf
-	; search for first system file
-	mov ah, 0x04
-	call loadf
+		; load root directory
+		call loadr
 
-	; restore drive number
-	mov dl, [bp+bpb7_dn]
+		; search for first system directory
+		mov ah, 0x14
+		call loadf
+		; search for first system file
+		mov ah, 0x04
+		call loadf
 
-	; restore potential partition table
-	pop si
-	pop ds
+		; restore drive number
+		mov dl, [bp+bpb.drivenum]
 
-	jmp 0x7C00
+		; restore potential partition table
+		pop si
+		pop ds
 
-	; Padding and signature
-	times (0x1FE - ($-$$)) db 0
-	dw 0xAA55
+		jmp 0x7C00
+
+		; Padding and signature
+		times (0x1FE - ($-$$)) db 0
+		dw 0xAA55
 buf:
diff --git a/inc/bpb.asm b/inc/bpb.asm
index 01f2f51..62d8232 100644
--- a/inc/bpb.asm
+++ b/inc/bpb.asm
@@ -1,29 +1,17 @@
-; DOS 3.31 Bios Parameter Block
-bpb_ss:	  equ 0x00 ; WORD sector size
-bpb_sc:	  equ 0x02 ; BYTE sector / cluster
-bpb_rsc:  equ 0x03 ; WORD reserved sector count
-bpb_fn:	  equ 0x05 ; BYTE fat number
-bpb_rde:  equ 0x06 ; WORD root dir entries
-bpb_ts:	  equ 0x08 ; WORD total sectors
-bpb_md:   equ 0x0A ; BYTE media descriptor
-bpb_sf:	  equ 0x0B ; WORD sectors / fat
-bpb_spt:  equ 0x0D ; WORD sectors per track
-bpb_nos:  equ 0x0F ; WORD number of sides
-bpb_po:   equ 0x11 ; DWORD partition offset
-bpb_lts:  equ 0x15 ; DWORD large total sectors
-
-; DOS 4.0 Extended Bios Parameter Block
-bpb4_dn:  equ 0x19 ; BYTE drive number
-bpb4_sig: equ 0x1B ; BYTE 29h
-bpb4_ser: equ 0x1C ; DWORD serial
-
-; DOS 7.1 Extended Bios Parameter Block
-bpb7_lsf: equ 0x19 ; DWORD large sectors / fat
-bpb7_rdc: equ 0x21 ; DWORD root directory cluster
-bpb7_fsc: equ 0x25 ; WORD fsinfo sector
-bpb7_bsc: equ 0x27 ; WORD backup boot sector
-bpb7_dn:  equ 0x35 ; BYTE drive number
-bpb7_sig: equ 0x37 ; BYTE 28h or 29h
-bpb7_ser: equ 0x38 ; DWORD serial
-
-bpb_len:  equ 0x4F
+struc bpb
+.sectorsize:	resw 1 ; WORD sector size
+.clustersects:	resb 1 ; BYTE sector / cluster
+.reservedsects:	resw 1 ; WORD reserved sector count
+.fatnumber:	resb 1 ; BYTE fat number
+.direntries:	resw 1 ; WORD root dir entries
+.total:		resw 1 ; WORD total sectors
+.mediadesc:	resb 1 ; BYTE media descriptor
+.fatsectors:	resw 1 ; WORD sectors / fat
+.tracksectors:	resw 1 ; WORD sectors per track
+.heads:		resw 1 ; WORD number of sides
+.sectoroffset:	resd 1 ; DWORD partition offset
+.longtotal:	resd 1 ; DWORD large total sectors
+.drivenum:	resb 1 ; BYTE drive number
+.signature:	resb 1 ; BYTE 28h
+.serial:	resd 1 ; DWORD serial
+endstruc