timer.c

// timer.c -- Initialises the PIT, and handles clock updates.
// Written for JamesM's kernel development tutorials.

#include "timer.h"
#include "write.h"

uint32_t tick = 0;

void timer_callback()
{
	tick++;
	//kprintf("Tick: %d\n", tick);
}

void init_timer(uint32_t frequency)
{
	fb_write("Initialising timer...");
  // Firstly, register our timer callback.
	//install_irq_handler(0, &timer_callback);

	// The value we send to the PIT is the value to divide it's input clock
	// (1193180 Hz) by, to get our required frequency. Important to note is
	// that the divisor must be small enough to fit into 16-bits.
	uint32_t divisor = 1193180 / frequency;

	// Send the command byte.
	outb(0x43, 0x36);

	// Divisor has to be sent byte-wise, so split here into upper/lower bytes.
	uint8_t l = (uint8_t)(divisor & 0xFF);
	uint8_t h = (uint8_t)( (divisor>>8) & 0xFF );

	// Send the frequency divisor.
	outb(0x40, l);
  outb(0x40, h);
	fb_write("Success!\n");
}