From 50aa6e4eecd3ba54efe2423e86fe73a41c2a9e43 Mon Sep 17 00:00:00 2001
From: Nero <41307858+nero@users.noreply.github.com>
Date: Sun, 25 Oct 2020 09:15:33 +0000
Subject: [PATCH] Use uppercase non-struct constants for BPB

---
 boot/fat.asm   | 30 ++++++++++++-------------
 boot/mbr.asm   | 12 +++++-----
 inc/bpb.asm    | 40 +++++++++++++++++++++------------
 kernel/fat.asm | 60 --------------------------------------------------
 4 files changed, 47 insertions(+), 95 deletions(-)
 delete mode 100644 kernel/fat.asm

diff --git a/boot/fat.asm b/boot/fat.asm
index d06e5dd..1a422b3 100644
--- a/boot/fat.asm
+++ b/boot/fat.asm
@@ -19,7 +19,7 @@ bootsect:	equ 0x7C00 ; our origin before reloc
 
 		times ( 0x0B - ($-$$) ) db 0
 
-params:		times bpb_size db 0
+bpb:		times BPBSIZ4 db 0
 
 		; Area for BPB
 		times ( 0x3E - ($-$$) ) db 0
@@ -54,15 +54,15 @@ read:		push ax
 		push dx
 
 		xchg ax, bx
-		mov al, byte [bp+bpb.heads]
-		mul byte [bp+bpb.tracksectors]
+		mov al, byte [bp+BPBNOS]
+		mul byte [bp+BPBSPT]
 		xchg ax, bx
 
 		; dx:ax = lba
 		div word bx
 		xchg ax, dx
 		; dx = cylinder, ax = head * tracksectors + sector
-		div byte [bp+bpb.tracksectors]
+		div byte [bp+BPBSPT]
 		; dx = cylinder, al = head, ah = sector
 		xchg dl, dh
 		ror dl, 1
@@ -92,7 +92,7 @@ read:		push ax
 		loop read
 		ret
 
-rootdirsects:	mov bx, [bp+bpb.direntries]
+rootdirsects:	mov bx, [bp+BPBRDE]
 		mov cl, 4
 		shr bx, cl ; 32 bytes per entry
 		ret
@@ -103,16 +103,16 @@ offset_cluster:	; add offset of cluster data area to DX:AX
 		adc dx, 0
 offset_rootdir:	; add length of fat table times number of fats
 		xor ch, ch
-		mov cl, byte [bp+bpb.fatnumber]
-.loop:		add ax, [bp+bpb.fatsectors]
+		mov cl, byte [bp+BPBFN]
+.loop:		add ax, [bp+BPBFS]
 		adc dx, 0
 		loop .loop
 offset_fat:	; add reserved sectors
-		add ax, [bp+bpb.reservedsects]
+		add ax, [bp+BPBRSC]
 		adc dx, 0
 offset_part:	; add partition offset
-		add ax, [bp+bpb.sectoroffset]
-		add dx, [bp+bpb.sectoroffset+2]
+		add ax, [bp+BPBHS]
+		add dx, [bp+BPBHS]
 		ret
 
 resetbuf:	; DS = ES
@@ -127,7 +127,7 @@ resetbuf:	; DS = ES
 		xor dx, dx
 		ret
 
-main:		mov bp, params
+main:		mov bp, bpb
 		mov [bp-1], dl
 
 		; load root directory
@@ -140,7 +140,7 @@ main:		mov bp, params
 
 		; search for file
 		pop bx
-		mov cx, [bp+bpb.direntries]
+		mov cx, [bp+BPBRDE]
 .loop:		push cx
 		mov si, filename
 		mov di, bx
@@ -156,7 +156,7 @@ main:		mov bp, params
 		call resetbuf
 		push di
 		call offset_fat
-		mov cx, [bp+bpb.fatsectors]
+		mov cx, [bp+BPBFS]
 		call read
 
 		; fetch cluster numbers (FAT12-specific)
@@ -189,10 +189,10 @@ readfat:	stosw
 loadclus:	lodsw
 		sub ax, 2
 		jc .jump
-		mul byte [bp+bpb.clustersects]
+		mul byte [bp+BPBSC]
 		call offset_cluster
 		xor cx, cx
-		mov cl, [bp+bpb.clustersects]
+		mov cl, [bp+BPBSC]
 		call read
 		jmp loadclus
 
diff --git a/boot/mbr.asm b/boot/mbr.asm
index 3b7caf9..f35e8aa 100644
--- a/boot/mbr.asm
+++ b/boot/mbr.asm
@@ -10,7 +10,7 @@
 
 	%include "inc/bpb.asm"
 
-	%define params	bs+0x0B
+	%define bpb	bs+0x0B
 
 	cpu 8086
 	org 0x0600
@@ -72,11 +72,11 @@ main:	; find active partition
 
 	; FAT bpb has "bytes per sector" at this place
 	; we support only 512 byte sectors anyways
-	cmp word [params+bpb.sectorsize], 512
+	cmp word [bpb+BPBSS], 512
 	jne chain
 
 	; Media descriptor byte is never smaller than 0xF0
-	cmp byte [params+bpb.mediadesc], 0xF0
+	cmp byte [bpb+BPBMD], 0xF0
 	jc chain
 
 	; ask BIOS what our disk geometry is
@@ -92,17 +92,17 @@ main:	; find active partition
 	; update sectors per track
 	xor ax, ax
 	mov al, cl
-	mov [params+bpb.tracksectors], ax
+	mov [bpb+BPBSPT], ax
 
 	; update number of sides
 	xor ax, ax
 	mov al, dh
-	mov [params+bpb.heads], ax
+	mov [bpb+BPBNOS], ax
 
 	; update partition offset
 	push si
 	add si, 0x08
-	mov di, params+bpb.sectoroffset
+	mov di, bpb+BPBHS
 	movsw
 	movsw
 	pop si
diff --git a/inc/bpb.asm b/inc/bpb.asm
index f2e170a..ba80e22 100644
--- a/inc/bpb.asm
+++ b/inc/bpb.asm
@@ -1,14 +1,26 @@
-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
-endstruc
+BPBOFF	equ 0xB
+
+; DOS 2.0 BPB
+BPBSS	equ 0 ; word
+BPBSC	equ 2 ; byte
+BPBRSC	equ 3 ; word
+BPBFN	equ 5 ; byte
+BPBRDE	equ 6 ; word
+BPBTS	equ 8 ; word
+BPBMD	equ 10 ; byte
+BPBFS	equ 11 ; word
+BPBSIZ2	equ 13 ; size constant
+
+; DOS 3.31 BPB
+BPBSPT	equ 0x0D ; word
+BPBNOS	equ 0x0F ; word
+BPBHS	equ 0x11 ; dword
+BPBLTS	equ 0x15 ; dword
+BPBSIZ3	equ 25 ; size constant
+
+; DOS 3.4 EBPB
+BPBDN	equ 0x19 ; byte
+BPBFALG	equ 0x1A ; byte
+BPBSIG	equ 0x1B ; byte
+BPBSER	equ 0x1C ; dword serial number
+BPBSIZ4	equ 32 ; size constant
diff --git a/kernel/fat.asm b/kernel/fat.asm
deleted file mode 100644
index 8a1c546..0000000
--- a/kernel/fat.asm
+++ /dev/null
@@ -1,60 +0,0 @@
-section .text
-
-load_bpb:	mov bx, [drive_ptr]
-		; read word for "sectors per fat"
-		mov ax, [diskbuf+0x016]
-		xor dx, dx
-		; if zero, we need to check dword in BPB 7.1
-		test ax, ax
-		jnz .short_sf
-		; fail if BPB 7.1 signature is not present
-		mov cl, [diskbuf+0x042]
-		or cl, 1
-		cmp cl, 0x29
-		jne .err
-		; load dword
-		mov ax, [diskbuf+0x024]
-		mov dx, [diskbuf+0x026]
-.short_sf:
-		; store local value
-		mov [bx+drive.fat_size], ax
-		mov [bx+drive.fat_size+2], dx
-
-		; copy number of fat's
-		xor ah, ah
-		mov al, [diskbuf+0x010]
-		mov [bx+drive.fat_num], ax
-
-		; copy number of root directory entries
-		mov ax, [diskbuf+0x011]
-		mov cl, 4
-		shr ax, cl
-		mov [bx+drive.dir_size], ax
-
-		; calculate offsets for everything
-		xor ax, ax
-		xor dx, dx
-		; add reserved sectors
-		add ax, [diskbuf+0x0B+bpb_rsc]
-		adc ax, 0
-		; save begin of FAT tables
-		mov [bx+drive.fat_offset], ax
-		mov [bx+drive.fat_offset+2], dx
-		; add FAT size * FAT number
-		mov cx, [bx+drive.fat_num]
-.floop:		add ax, [bx+drive.fat_size]
-		adc dx, [bx+drive.fat_size+2]
-		loop .floop
-		; save begin of root directories
-		mov [bx+drive.dir_offset], ax
-		mov [bx+drive.dir_offset+2], dx
-		; add root directory size (might be zero)
-		add ax, [bx+drive.dir_size]
-		adc dx, 0
-		; save start of data area
-		mov [bx+drive.clus_offset], ax
-		mov [bx+drive.clus_offset+2], dx
-
-		ret
-.err:		stc
-		ret