#include "system.h"

#define PIT_CHANNEL0_REG 0x40

#define PIT_CHANNEL1_REG 0x41

#define PIT_CHANNEL2_REG 0x42

#define PIT_COMMAND_REG 0x43

#define PIT_FREQUENCY 1193180

/* command register

* 7, 6: counter number (0-2)

* 5, 4: read write mode, 0 = latch ocunt value, 1 = lsb, 2 = msb, 3 = lsb then msb

* 3, 2, 1: mode,

* 0 = interrupt on terminal count

* 1 = hardware retriggerable one shot

* 2 = rate generator

* 3 = square wave generator

* 4 = software triggered strobe

* 5 = hardware triggered strobe

* 1, 0: 0 = 16 bit counter, 1 = 4-digit BCD counter

*/

/* from brokenthorn.com

* Each counter register holds the COUNT value used by the PIT to count

* down from. They are all 16-bit registers. When writing or reading from

* these registers, you must first send a control word to the PIT. You

* might wonder why we cannot just do it directly. There is a reason for

* this, and it has to do with the size of the data. The PIT only has 8 data

* lines (Pins D0-D7). However, the counter registers are all 16 bits, not 8.

*/

void pit_setup(unsigned short frequency) {

unsigned short divided = PIT_FREQUENCY / frequency;

// use square wave mode

unsigned short control_word = 0b00110110;

outb(control_word, PIT_COMMAND_REG);

outb(divided && 0xff, PIT_CHANNEL0_REG);

outb(divided >> 8, PIT_CHANNEL0_REG);

timer_ticks = 0;

}

void timer_wait(unsigned ticks) {

unsigned eticks = timer_ticks ticks;

while (timer_ticks < eticks) ;

}