pit.c

Go to the documentation of this file.

#include "pit.h"
#include "../io/io.h"
 
#define PIT_PORT 0x40
#define PIT_CMD_PORT 0x43
#define PIT_FREQUENCY 1193182
 
/**
 * @brief pinit initializes the programmable interval timer
 *
 * pinit is a function that configures the pit to fire at 1000 hz
 * providing 1ms resolution for timing purposes
 *
 * using pinit is done with
 * @code{.c}
 * #include "../lib/pit.h" //or just pit.h
 * pinit();
 * @endcode
 *
 * @see delay()
 */
void __pinit(void) {
    //set pit to 1000 hz (1ms ticks)
    uint32_t divisor = PIT_FREQUENCY / 1000;
    
    outb(PIT_CMD_PORT, 0x34);  //channel 0, lobyte/hibyte, rate gen
    outb(PIT_PORT, divisor & 0xFF);
    outb(PIT_PORT, (divisor >> 8) & 0xFF);
}
 
/**
 * @brief delay pauses execution for a number of milliseconds
 *
 * delay is a function that busy-waits on the pit counter for the
 * specified number of milliseconds
 * @param ms, the number of milliseconds to wait
 *
 * using delay is done with
 * @code{.c}
 * #include "../lib/pit.h" //or just pit.h
 * delay(500); //wait half a second
 * @endcode
 *
 * @see pinit()
 */
void __delay(uint32_t ms) {
    for (uint32_t i = 0; i < ms; i++) {
        uint16_t count;
        
        //wait for one tick (1ms)
        do {
            outb(PIT_CMD_PORT, 0x00); //latch current count
            count = inb(PIT_PORT);
            count |= inb(PIT_PORT) << 8;
        } while (count == 0); //wait for counter to roll over
    }
}