How to handle keyboard in real mode through BIOS i

Question

I have to code for a operating system on which I can run a calculater.It is like a desktop calculater. For this I am reading the brokenthorn operating development series I have completed the second stage of bootloader The bootloader is in real mode. After this the author is explaining the protected mode. I don't want to use the protected mode. I don't have time for that. So I want to write the calculater in real mode by using bios interrupts. Is it possible? I think it can be written on the second stage of the bootloader(I am not sure.) Means I don't have to use a kernel(I am not sure). I don't know how to use BIOS interrupts to handle the keyboard. Can anybody provide me a link which will help me in this? And If anything wrong in whatevet I assumed above is wrong, please correct me.Thanks in advance.

Answer 1

You can handle IRQ 1 (mapped to interrupt 9 by the x86 controller) and read the keys from port 60h.

See http://inglorion.net/documents/tutorials/x86ostut/keyboard/.

Answer 2

Minimal GAS boot sector BIOS example

When you enter a character, it gets printed to the screen.

main.S

.code16
.global _start
_start:
cli

/* Set SS and SP as they may get used by BIOS calls. */
xor %ax, %ax
mov %ax, %ss
mov $0x0000, %sp

/* Get input to %al */
mov $0x00, %ah
int $0x16

/* Print the input from %al */
mov $0x0E, %ah
int $0x10

hlt

.org 510
.word 0xaa55

Compile and run:

as -o main.o main.S
ld --oformat binary -o main.img -Ttext 0x7C00 main.o
qemu-system-i386 -hda main.img

GitHub upstream.

Tested on Ubuntu 14.04 AMD64, Binutils 2.24, QEMU 2.0.0 and on real hardware Lenovo Thinkpad T400.

Answer 3

If you want to use high-level BIOS keyboard services, rather than handling the keyboard interrupts yourself, then INT 16h is what you want.

INT 16h with AH=00h or 10h will block waiting for a keypress (returns ASCII result in AL); use AH=01h or 11h to query whether a keypress is available first if you want to avoid blocking (returns immediately with ZF clear if a key is available, or set if not). See e.g. here, or here (or Google "INT 16h" for more).