#include <htc.h>

#define _XTAL_FREQ 8e6 // 8MHz
#define ZERO_CROSS_PIN GP0
#define ZERO_CROSS_PIN_TRIS TRISIO0
#define OUTPUT_PIN GP1
#define OUTPUT_PIN_TRIS TRISIO1

/*
   _delay( 1 ); // 1 instruction cycle delay
   __delay_us( 2 ); // 2 us delay
   __delay_ms( 3 ); // 3 ms delay
*/

unsigned char timerArmed = 0; // set if timer is waiting to go off
unsigned int delayTicks = 0; // number of ticks to set the timer to for the desired delay
unsigned int delayFor = 0; // delay for this many uS

int main (void)
{
    // -- Oscillator setup
    OSCCONbits.IRCF = 7; // set internal osc to 8MHz
    while (!OSCCONbits.HTS); // wait for osc to be stable

    // -- IO setup
    ZERO_CROSS_PIN_TRIS = 1; // read from Z_C_PIN
    OUTPUT_PIN_TRIS = 0; // write to O_P
    OUTPUT_PIN = 0; // set it to a known state

    // -- Timer1 setup
    T1CONbits.T1CKPS = 0; // 1:1 prescaler
    T1CONbits.T1OSCEN = 0; // disable Timer1 oscillator
    T1CONbits.TMR1CS = 0; // internal clock (fosc/4)

    // -- Timer1 interrupt setup
    TMR1 = 0; // clear timer1 counter
    TMR1IF = 0; // clear timer1 flag
    TMR1IE = 1; // enable timer1 interrupt
    PEIE = 1; // enable peripheral interrupts
    GIE = 1; // enable all interrupts

    while (1)
    {
        if (ZERO_CROSS_PIN && !timerArmed) // if we have a pulse and the
        {                                  // timer isnt armed, arm it
            delayFor = 4000; // in uS
            delayTicks = (2 * delayFor);
            TMR1 = (0xFFFF - delayTicks) + 1; // +1 to account for ffff->0 rollover
            T1CONbits.TMR1ON = 1; // arm timer1
            timerArmed = 1;
        }
    }

    return 0; // should never get here

}

void interrupt interrupt_handler(void)
{
    if (TMR1IE && TMR1IF) // if TMR1 caused the interrupt
    {
        OUTPUT_PIN = 1; // fire!
        __delay_us(10); // for the triac to catch up
        OUTPUT_PIN = 0; // triac will continue to conduct until current drops
        timerArmed = 0; // timer not armed anymore
        TMR1IF = 0; // clear interrupt flag
    }
}