Concepts you may want to Google beforehand: CPU timer, keyboard interrupts, scancode
Goal: Implement our first IRQ handlers: the CPU timer and the keyboard
Everything is now ready to test our hardware interrupts.
The timer is easy to configure. First we'll declare an init_timer() on cpu/timer.h and
implement it on cpu/timer.c. It is just a matter of computing the clock frequency and
sending the bytes to the appropriate ports.
We will now fix kernel/utils.c int_to_ascii() to print the numbers in the correct order.
For that, we need to implement reverse() and strlen().
Finally, go back to the kernel/kernel.c and do two things. Enable interrupts again
(very important!) and then initialize the timer interrupt.
Go make run and you'll see the clock ticking!
The keyboard is even easier, with a drawback. The PIC does not send us the ASCII code for the pressed key, but the scancode for the key-down and the key-up events, so we will need to translate those.
Check out drivers/keyboard.c where there are two functions: the callback and
the initialization which configures the interrupt callback. A new keyboard.h was
created with the definitions.
keyboard.c also has a long table to translate scancodes to ASCII keys. For the time
being, we will only implement a simple subset of the US keyboard. You can read
more about scancodes here
I don't know about you, but I'm thrilled! We are very close to building a simple shell. In the next chapter, we will expand a little bit on keyboard input