kernel: First steps of calculating drive tab data from BPB

boot/kernel.asm

@@ -2,9 +2,28 @@
 		org 0x500
 
 %include	"inc/bpb.asm"
-%include	"inc/mbr.asm"
 %include	"inc/dpt.asm"
 
+; drive table entry
+struc drive
+.biosnum:	resb 1
+.flag:		resb 1
+.spc:		resw 1
+.cylinders:	resw 1
+.dpt:		resb dpt_size
+.type:		resb 1 ; 12 or 16, depending on FAT type
+.fat_offset:	resd 1 ; offset of fat table
+.fat_num:	resw 1 ; number of fat tables
+.fat_size:	resw 1 ; sectors per fat table
+
+.dir_offset:	resd 1 ; offset of root directory
+.dir_size:	resw 1 ; size of root directory in sectors
+
+.clus_offset:	resd 1 ; offset of clusters
+.clus_num:	resw 1 ; number of clusters
+.clus_size:	resw 1 ; sectors per cluster
+endstruc
+
 		; kernel stack size in words
 %define		stacksize 512
 
@@ -240,6 +259,7 @@ fputc:	push ax
 	iret
 
 	%include "kernel/drive.asm"
+	%include "kernel/fat.asm"
 
 zero:	dw 0
 

kernel/drive.asm

@@ -2,15 +2,6 @@ section .bss
 
 drives:		equ 16
 
-; drive table entry
-struc drive
-.biosnum:	resb 1
-.flag:		resb 1
-.spc:		resw 1
-.cylinders:	resw 1
-.dpt:		resb dpt_size
-endstruc
-
 		; ptr into currently selected drive
 drive_ptr:	resw 1
 

kernel/fat.asm

@@ -1,111 +1,59 @@
-	section .bss
-
-	; the sector numbers have the partition offset already included
-
-fat_offset:
-	resd 1
-fat_size:
-	resd 1
-fat_num: ; a byte would be enough, but i want to work with cx
-	resw 1
-
-rootdir_offset:
-	resd 1
-rootdir_size:
-	resw 1
-
-clusters_offset:
-	resd 1
-clusters_num:
-	resd 1
-
 section .text
 
-load_ts: ; load total number of sectors into DX:AX
+load_bpb:	mov bx, [drive_ptr]
-	xor dx, dx
-	mov ax, [disk_buffer+0x013]
-	test ax, ax
-	jnz .ret
-	mov ax, [disk_buffer+0x020]
-	mov dx, [disk_buffer+0x022]
-.ret:	ret
-
-	; invoked after disk select
-load_bpb:
 		; read word for "sectors per fat"
-	mov ax, [disk_buffer+0x016]
+		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, [disk_buffer+0x042]
+		mov cl, [diskbuf+0x042]
 		or cl, 1
 		cmp cl, 0x29
 		jne .err
 		; load dword
-	mov ax, [disk_buffer+0x024]
+		mov ax, [diskbuf+0x024]
-	mov dx, [disk_buffer+0x026]
+		mov dx, [diskbuf+0x026]
 .short_sf:
 		; store local value
-	mov [fat_size], ax
+		mov [bx+drive.fat_size], ax
-	mov [fat_size+2], dx
+		mov [bx+drive.fat_size+2], dx
 
 		; copy number of fat's
 		xor ah, ah
-	mov al, [disk_buffer+0x010]
+		mov al, [diskbuf+0x010]
-	mov [fat_num], ax
+		mov [bx+drive.fat_num], ax
 
 		; copy number of root directory entries
-	mov ax, [disk_buffer+0x011]
+		mov ax, [diskbuf+0x011]
 		mov cl, 4
 		shr ax, cl
-	mov [rootdir_size], ax
+		mov [bx+drive.dir_size], ax
 
 		; calculate offsets for everything
-	mov ax, [part_offset]
+		xor ax, ax
-	mov dx, [part_offset+2]
+		xor dx, dx
 		; add reserved sectors
-	add ax, [disk_buffer+0x0B+bpb_rsc]
+		add ax, [diskbuf+0x0B+bpb_rsc]
 		adc ax, 0
 		; save begin of FAT tables
-	mov [fat_offset], ax
+		mov [bx+drive.fat_offset], ax
-	mov [fat_offset+2], dx
+		mov [bx+drive.fat_offset+2], dx
 		; add FAT size * FAT number
-	mov cx, [fat_num]
+		mov cx, [bx+drive.fat_num]
-.floop:	add ax, [fat_size]
+.floop:		add ax, [bx+drive.fat_size]
-	adc dx, [fat_size+2]
+		adc dx, [bx+drive.fat_size+2]
 		loop .floop
 		; save begin of root directories
-	mov [rootdir_offset], ax
+		mov [bx+drive.dir_offset], ax
-	mov [rootdir_offset+2], dx
+		mov [bx+drive.dir_offset+2], dx
 		; add root directory size (might be zero)
-	add ax, [rootdir_size]
+		add ax, [bx+drive.dir_size]
 		adc dx, 0
 		; save start of data area
-	mov [clusters_offset], ax
+		mov [bx+drive.clus_offset], ax
-	mov [clusters_offset+2], dx
+		mov [bx+drive.clus_offset+2], dx
-
-	call load_ts
-	add ax, [part_offset]
-	adc dx, [part_offset+2]
-	sub ax, [clusters_offset]
-	sbb dx, [clusters_offset+2]
-
-	; get "sectors per cluster"
-	mov cl, [disk_buffer+0x00D]
-	; this turns dx:ax from data sectors to number of clus
-.sloop:	shr cl, 1
-	test cl, cl
-	jz .send
-	clc
-	rcr dx, 1
-	rcr ax, 1
-	jmp .sloop
-.send:  mov [clusters_num], ax
-	mov [clusters_num+2], dx
-
-	int 3
 
 		ret
 .err:		stc