Luna/kernel/src/scheduling/PIT.cpp

#define MODULE "pit"

#include "scheduling/PIT.h"
#include "io/IO.h"
#include "log/Log.h"

#define PIT_CHANNEL_0_PORT 0x40

volatile uint64_t PIT::ms_since_boot = 0;
uint16_t divisor = 65535;

void PIT::initialize(uint64_t frequency)
{
    divisor = base_frequency / frequency;
    kinfoln("Configuring PIT to use divisor %d (will tick %lu times per second)", divisor, frequency);
    if (divisor < 100) divisor = 100;
    IO::outb(PIT_CHANNEL_0_PORT, (uint8_t)(divisor & 0xFF));
    IO::delay();
    IO::outb(PIT_CHANNEL_0_PORT, (uint8_t)((divisor & 0xFF00) >> 8));
}

uint64_t PIT::frequency()
{
    return base_frequency / divisor;
}

void PIT::tick()
{
    ms_since_boot += 1000 / frequency();
}