Another attempt on disk i/o

boot/kernel.asm

@@ -3,6 +3,7 @@
 	jmp 0:(init+0x7C00-$$)
 
 	%include "inc/bpb.asm"
+	%include "inc/mbr.asm"
 
 	; Far call via interrupt vector
 	%macro intcall 1
@@ -195,7 +196,7 @@ fputc:	push ax
 	%include "kernel/diskio.asm"
 
 vects:	dw int20h, int21h, retf, retf
-	dw retf, int25h, int26h, int20h
+	dw retf, retf, retf, int20h
 	dw idle, fputc
 
 main:	; zero out first 64kb except our code
@@ -222,12 +223,7 @@ intlp:	movsw
 
 	call dnconv
 	mov al, dl
-	mov cx, 1
+	call select
-	mov dx, 0
-	mov bx, buffer
-	int 3
-	intcall 0x25
-	int 3
 
 loop:	int 0x28
 	jmp loop
@@ -250,6 +246,3 @@ init:	cli
 section .bss
 	; stack to be used during init and disk i/o
 stack:	resw stacks
-	; default int 25h/26h handler use a cache to keep geometry for
-	; the first 4 drives
-buffer:	resb 512

inc/mbr.asm

@@ -0,0 +1,11 @@
+mbrtab:	equ 0x1BE	; start of partition table
+mbrsig:	equ 0x1FE	; start of signature
+mbrmn:	equ 0x55AA	; signature value
+
+pardn:	equ 0x00	; byte: partition active flag
+parchs:	equ 0x01	; 3 bytes: CHS for first sector
+partyp:	equ 0x04	; byte: partition type
+parend:	equ 0x05	; 3 bytes: CHS for last sector
+paroff:	equ 0x08	; dword: partition offset in sectors
+parlen:	equ 0x0C	; dword: partition length in sectors
+parsiz:	equ 0x10

kernel/diskio.asm

@@ -1,11 +1,23 @@
 	section .bss
 
-chsspt: equ 0 ; word sectors per track
+disk_buffer:
-chsnos: equ 2 ; word number of sides
+	resb 512
-chspo:  equ 4 ; dword partition offset
-chssiz: equ 8
 
-chstab: resw (4*chssiz)
+disk_current:
+	resb 1
+
+lba_supported:
+	resb 1
+
+disk_chs: ; DL, DH, CL, CH for int 13h CHS functions
+	resb 4
+disk_dap: ; disk access packet for int 13h EBIOS functions
+	resb 0x10
+
+disk_tracks: ; heads * spt
+	resw 1
+disk_spt:
+	resb 1
 
 	; Disk access packet for EBIOS extensions
 dapps:	equ 0 ; byte packet size
@@ -28,121 +40,77 @@ dncl:	rcl dl, 1
 	xchg dh, dl
 	ret
 
-fndchs:	; find CHS table entry
+	; Select a drive for I/O
-	; IN	dl	DOS drive number (A=0, B=1, ...)
+	; IN	dl	0=A, 1=B, 2=C, 3=D
-	; OUT	cs:si	ptr to chs table entry
+select:	mov byte [disk_current], 0xFF
-	push ax
+	mov byte [lba_supported], 0
-	mov ax, chssiz
+	cmp dl, 0x02
-	mul dl
+	jc select_floppy
-	add ax, chstab
+	; detect EBIOS/LBA extensions
-	mov si, ax
-	pop ax
-	ret
-
-	; compare sector number in disk access packet with zero
-	; sets zero flag accordingly
-iszero:	push ax
-	mov ax, [bx]
-	or ax, [bx+2]
-	pop ax
-	ret
-
-	; calculate CHS from dap and CHS table entry
-	; IN	ds:bx	disk access packet
-	;	cs:si	chstab table entry
-	; OUT	cx,dh	chs data for int 13h
-calchs:	push ax
-	; load linear sector number
-	mov dx, [bx+2]
-	mov ax, [bx]
-	; if any word of it is non-zero, we need to do calculation
-	call iszero
-	jz .zero
-	; ax is track number (lba / spt)
-        ; dx is sector (lba % spt) + 1
-	div word [cs:si+chsspt]
-	inc dx
-	; sector number
-	mov cl, dl
-	; ax is cylinder (track / heads)
-	; dx is head (track % heads)
-	xor dx, dx
-	div word [cs:si+chsnos]
-	; set up cylinder and head number
-	mov ch, al
-	mov dh, dl
-	pop ax
-	ret
-	; set up CHS data for int 13h for reading sector zero
-.zero:	mov cx, 1 ; C=0, S=1
-	mov dh, 0 ; H=0
-	pop ax
-	ret
-
-	; ABSOLUTE DISK READ / DISK WRITE
-int25h:	mov ah, 2
-	jmp adisk
-int26h:	mov ah, 3
-adisk:	push bp
-	push ds
-	push es
-	mov bp, sp
-
-	push ax
-
-	cmp cx, 0xFFFF
-	je .lrg
-
-	; build ebios DAP from registers supplied
-	; qword sector number
-	push cs
-	push cs
-	push cs
-	push dx
-	; dword target buffer
-	push ds
-	push bx
-	; word number of sectors
-	push cx
-	jmp .psz
-
-.lrg:	; build ebios DAP from int 25h DAP
-	; qword sector number
-	push cs
-	push cs
-	mov ax, [bx+2]
-	push ax
-	mov ax, [bx]
-	push ax
-	; dword target buffer
-	mov ax, [bx+8]
-	push ax
-	mov ax, [bx+6]
-	push ax
-	; word number of sectors
-	mov ax, [bx+4]
-	push ax
-.psz:	; word packet size
-	mov ax, dapsiz
-	push ax
-
-	; DS:SI = SS:SP (ptr to dap)
-	push ss
-	pop ds
-	mov si, sp
-
-	; set up int 13h subfunction number
-	mov ax, [si+dapsiz]
-	add ah, 0x40
-
-	; get BIOS drive number
-	mov dl, al
 	call dnconv
-
+	mov byte [disk_chs], dl
+	mov ah, 0x41
+	mov bx, 0x55AA
 	int 0x13
+	test cx, 1
+	jz .nolba
+	cmp bx, 0xAA55
+	jnz .nolba
+	mov byte [lba_supported], 1
+.nolba:	call seek_zero
+	ret
 
-.ret:	mov sp, bp
+select_floppy:
+	xor dx, dx
+	xor ax, ax
+	call seek
+	call read
+	ret
+
+	; Set absolute sector number
+	; IN	dx:ax	32-bit sector number
+seek:	push ax
+	or ax, dx
+	pop ax
+	jz seek_zero
+
+	; dx:ax = lba
+	div word [disk_tracks]
+	xchg ax, dx
+	; dx = cylinder, ax = head * spt + sector
+	div byte [disk_spt]
+	; dx = cylinder, al = head, ah = sector
+	xchg dl, dh
+	ror dl, 1
+	ror dl, 1
+	or dl, ah
+	;inc dx
+	; dh bit 0-7: cylinder 0-7
+	; dl bit 0-5: sector number 0-5
+	; dl bit 6-7: cylinder 8-9
+	; store
+	mov byte [disk_chs+1], al
+	mov word [disk_chs+2], dx
+	int 3
+	ret
+
+seek_zero:
+	mov byte [disk_chs+1], 0
+	mov word [disk_chs+2], 1
+	ret
+
+	; Read a sector into buffer
+read:	mov ax, 0x0201
+	mov dx, [disk_chs]
+	mov cx, [disk_chs+2]
+	lea bx, [disk_buffer]
+	push cs
 	pop es
-	pop ds
+	int 3
-	pop bp
+	int 0x13
-	retf
+	int 3
+	ret
+
+	; Write a sector into buffer
+write:
+	ret