timer.c

#include "printk.h"
#include "isr.h"
#include "types.h"
#include "ports.h"
#include "timer.h"

#define PIT_A       0x40
#define PIT_B       0x41
#define PIT_C       0x42
#define PIT_CONTROL 0x43
#define PIT_SET     0x36
#define PIT_MASK    0xFF
#define PIT_SCALE   1193180

static clock_t tick = 0;

static void
timer_callback(struct registers *regs)
{
    ++tick;

    if (tick % 100 == 0)
        printk(INFO, "Tick: %lu\n", tick);
}

void 
timer__init(uint32_t frequency)
{
    int32_t divisor;

    printk(INFO, "Initalizing timer\n");
    register_interrupt_handler(IRQ0, &timer_callback);

    divisor = PIT_SCALE / frequency;
    
    outb(PIT_CONTROL, PIT_SET);

    outb(PIT_A, divisor & PIT_MASK);
    outb(PIT_A, (divisor >> 8) & PIT_MASK);
}