mirror of
https://github.com/cfenollosa/os-tutorial.git
synced 2024-10-27 20:34:19 +00:00
40 lines
1.6 KiB
Markdown
40 lines
1.6 KiB
Markdown
*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.
|
|
|
|
Timer
|
|
-----
|
|
|
|
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!
|
|
|
|
|
|
Keyboard
|
|
--------
|
|
|
|
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](http://www.win.tue.nl/~aeb/linux/kbd/scancodes-1.html)
|
|
|
|
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
|