Computer makes clicking sound when using INT16h 00h

Question

I'm using x86 to make a cat program, hoping to turn it into a basic OS. I copied the starter code from MikeOS, and added some stuff of my own. It works fine with qemu, but when actually using a USB with the code copied to it, the computer clicks every time I press a key. Any ideas?

    BITS 16

start:
mov ax, 07C0h       ; Set up 4K stack space after this bootloader
add ax, 288     ; (4096 + 512) / 16 bytes per paragraph
mov ss, ax
mov sp, 4096

mov ax, 07C0h       ; Set data segment to where we're loaded
mov ds, ax


mov si, text_string ; Put string position into SI
call print_string   ; Call our string-printing routine


typel:
mov ah, 00h     ; Set mode to read from keyboard
int 16h         ; Read from keyboard
mov ah, 0Eh     ; Set up printing
int 10h         ; Print
jmp typel       ; Typing loop


text_string db 'Starting SR|02',10,13,7,0


print_string:           ; Routine: output string in SI to screen
mov ah, 0Eh     ; int 10h 'print char' function

.repeat:
lodsb           ; Get character from string
cmp al, 0
je .done        ; If char is zero, end of string
int 10h         ; Otherwise, print it
jmp .repeat

.done:
ret


times 510-($-$$) db 0   ; Pad remainder of boot sector with 0s
dw 0xAA55       ; The standard PC boot signature

Using American Megatrends Inc. Version: 1504

Maybe this is related: https://stackoverflow.com/questions/47277702/custom-bootloader-booted-via-usb-drive-produces-incorrect-output-on-some-compute/47320115#47320115 — Michael Petch, Jun 14 '18 at 03:59
Although not likely related to your issue, if you are using int 10h/ah=-0eh you should set the page number to 0 (BH) per the docs: http://www.ctyme.com/intr/rb-0106.htm — Michael Petch, Jun 14 '18 at 04:04
Cat now works, but the original text display system broke. 'Starting SR|02' no longer displays. — Metroidisprettycool, Jun 14 '18 at 04:11
You should also make sure before you use a string instruction like `lodsb` that you use `cld` before to ensure the direction bit is set forward. put `cld` after `mov ds, ax` — Michael Petch, Jun 14 '18 at 04:16
"nasm -f bin -o os.bin os.asm" to make the .bin, and "sudo dd if=os.bin of=/dev/sdg bs=512 count=1" to add it to the MBR — Metroidisprettycool, Jun 14 '18 at 04:16

Computer makes clicking sound when using INT16h 00h

0 Answers0