int 13h - Read returning 0Ch Media type not found
Posted: Tue Dec 28, 2010 10:22 pm
Hi, I've just started learning assembly language and I wrote some NASM code to create an 8-MB fixed-size VHD file, for which I load into VirtualBox to run my assembly. The first sector contains the boot sector, and the second sector just contains a bunch of data I'd like to load into 0x0000:0x7E00 and display a character dump of. My INT 0x13 function 0x02 sector read, for some reason, doesn't work even though I'm following the IBM ROM BIOS book to the letter on how to use it. It fails with AL receiving 0x0C, "Media type not found," even though I save the boot drive number given to me from the BIOS. It also doesn't read the data when I dd the VHD to USB and boot off of it, so it must be something silly I'm doing. 
Here's the code. Thanks for any help!
Steven
Here's the code. Thanks for any help!
Steven
Code: Select all
;
; SECTOR #1
; nasm -f bin -o boot.vhd boot.asm
;
bits 16
org 0x7C00
start:
; set stack pointer ss:sp (stack segment:stack pointer)
cli
mov ax, 0x0000
mov ss, ax
mov sp, 0x7C00
sti
; save drive number
mov [boot_drive], dl
; set video mode to color text
mov ah, 0x00
mov al, 0x03
int 10h
; read sector
read_sector:
; reset disk
mov ah, 0x00
mov dl, [boot_drive]
int 0x13
; read sector
mov ah, 0x02 ; read sectors
mov al, 0x01 ; number of sectors to read
mov bx, 0x0000 ; read into 0x0000:0x7E00
mov es, bx ; read into 0x0000:0x7E00
mov bx, 0x7E00 ; read into 0x0000:0x7E00
mov dl, [boot_drive] ; read from hard drive
mov dh, 0x00 ; head
mov ch, 0x00 ; cylinder number lo (bits 0-7) cylinder number uses 10 bits for [0, 1024] cylinders
mov cl, 0x00 ; cylinder number hi (bits 6-7)
and cl, 0x02 ; set the sector number (bits 0-5) sector uses 6 bits for [1, 63] sectors
int 0x13 ; execute read sector
;jc read_sector
; address to take hex dump
mov si, 0x7E00
mov byte[row], 0x00
mov byte[col], 0x00
; for(;;) {
begin_loop:
; termination check
mov al, byte[row]
mov bl, byte[max_row]
cmp al, bl
jae end_loop
; col = 0
mov byte[col], 0x00
; for(;;) {
begin_col_loop:
; if(!(col < max_col)) break;
mov al, byte[col]
mov bl, byte[max_col]
cmp al, bl
jae end_col_loop
; set cursor position
mov dh, byte[row]
mov dl, byte[col]
mov bh, 0x00
mov ah, 0x02
int 10h
; display character
mov bh, 0x00
mov bl, 0xE4
mov cx, 0x01
mov al, byte[si]
mov ah, 0x09
int 10h
; increment address
inc si
; col++
inc byte[col]
; }
jmp begin_col_loop
end_col_loop:
; row++
inc byte[row]
; }
jmp begin_loop
end_loop:
; loop forever
loop_forever:
jmp loop_forever
; data
row db 0x00
col db 0x00
max_row db 0x10
max_col db 0x20
boot_drive db 0x00
times 510 - ($ - $$) db 0
dw 0xAA55
;
; SECTOR #2
;
times 1022 - ($ - $$) db 0x41
dw 0xAA55
;
; HARD DISK DATA
;
times 0x00800000 - ($ - $$) db 0
;
; VHD FOOTER
;
dq 0x78697463656E6F63 ; 8-byte conectix cookie
dd 0x02000000 ; 4-byte features (reserved)
dd 0x00000100 ; 4-byte file format version
dq 0xFFFFFFFFFFFFFFFF ; data offset for fixed disks
dd 0x17D06014 ; time stamp
dd 0x656E6F6E ; creator application (none in ASCII)
dd 0x00000100 ; creator version
dd 0x6B326957 ; creator host OS (Windows)
dq 0x0000800000000000 ; original size (8 MB)
dq 0x0000800000000000 ; current size (8 MB)
dd 0x1104F000 ; disk geometry (see below)
dd 0x02000000 ; disk type (fixed hard disk)
dd 0x00000000 ; checksum (skip)
dq 0x0123456789ABCDEF ; unique identifier part 1
dq 0x0123456789ABCDEF ; unique identifier part 2
db 0x00 ; saved state
times 427 db 0 ; reserved
; DISK GEOMETRY
; 0x00F0-04-11
; 240 cylinders
; 4 heads
; 17 sectors
; 512 bytes per sector
; 240*4*17*512 = bytes = 8355840 KB = 7 MB
I see A's now.