void init_timer(uint32_t frequency)
{
    // Firstly, register our 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.
    ioport_out(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.
    ioport_out(0x40, l);
    ioport_out(0x40, h);
}