// PIC18 in C - Versione 0.3 - Febbraio 2016
// Copyright (c) 2014, Vincenzo Villa
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/PIC18/interrupt.htm

// Reference
// PIC18F2xK20 / MPLAB X IDE v3.25 / XC8 1.35

// Timer0 and Timer1 interrupt

#include "configurationsbits-PIC18F25K20.h"

#define _XTAL_FREQ 1000000 // Main clock frequency (Default: 1 MHz)
#define TIMER0_VALUE 12345u // See text - ? Hz blink
#define TIMER1_VALUE 6789u // See text - ? Hz blink
#define MYDELAY __delay_ms(50) // 50 ms delay

void configureRegisters(void); // Configure PIC18 registers

void main(void) {

    configureRegisters();

    // Enable interrupt and timers
    GIEL = 1; // 1 = Enables all low priority interrupts
    GIEH = 1; // 1 = Enables all high (and low) priority interrupts

    TMR0ON = 1; // 1 = Enable Timer0
    TMR1ON = 1; // 1 = Enables Timer1 

    while (1) { // "Supercar", forever
        for (LATC = 0b00000001; LATC != 0; LATC <<= 1) MYDELAY; // Shift left, eight times
        for (LATC = 0b10000000; LATC != 0; LATC >>= 1) MYDELAY; // Shift right, eight times
    }
}

// ******** ISR High Priority ********
void interrupt __high_priority my_isr_h(void) {
    if (TMR1IF == 1) // Interrupt from Timer1?
    {
        TMR1H = TIMER1_VALUE >> 8; // Write 8 MSB to Timer1
        TMR1L = TIMER1_VALUE & 0xFF; // Write 8 LSB to Timer1

        LATB5 = ~LATB5; // Change LED B5 status
        TMR1IF = 0; // Clear interrupt status 
    }
}

// ******** ISR Low Priority ********
void interrupt __low_priority my_isr_l(void) {
    if (TMR0IF == 1) // Interrupt from Timer0?
    {
        TMR0H = TIMER0_VALUE >> 8; // Write 8 MSB to Timer0
        TMR0L = TIMER0_VALUE & 0xFF; // Write 8 LSB to Timer0

        LATB4 = ~LATB4; // Change LED B4 status
        TMR0IF = 0; // Clear interrupt status 
    }
}

// ******** Startuo congigurations ********
void configureRegisters(void) {

    // ******** Configure I/O Ports ********
    TRISC = 0; // Configure port C as output
    TRISB4 = 0; // Configure RB4 as output
    TRISB5 = 0; // Configure RB5 as output

    // ******** Configure Interrupts levels ********
    RCONbits.IPEN = 1; // 1 = Enable priority levels on interrupts 

    // ******** Configure Timer0 ********
    T08BIT = 0; // 0 = Timer0 is configured as a 16-bit timer/counter
    T0CS = 0; // 0 = Internal instruction cycle clock (_XTAL_FREQ / 4 = 250 kHz)
    PSA = 0; // 0 = Timer0 prescaler is assigned. Timer0 clock input comes from prescaler output
    T0CONbits.T0PS = 0b001; // 1:4 prescale value for Timer0

    TMR0H = TIMER0_VALUE >> 8; // Write 8 MSB to Timer0
    TMR0L = TIMER0_VALUE & 0xFF; // Write 8 LSB to Timer0

    TMR0IF = 0; // Clear interrupt status for Timer0

    TMR0IP = 0; // 0 = Set low priority interrupt for Timer0
    TMR0IE = 1; // 1 = Enables overflow interrupt for Timer0

    // ******** Configure Timer 1 ********
    TMR1CS = 0; // 0 =  Internal clock (FOSC/4) for Timer1
    T1CONbits.T1CKPS = 0b10; // 10 = 1:4 Prescale value for Timer1
    T1RUN = 0; // Main system clock is derived from another source
    T1OSCEN = 0; // Timer1 oscillator is shut off

    TMR1H = TIMER1_VALUE >> 8; // Write 8 MSB to Timer1
    TMR1L = TIMER1_VALUE & 0xFF; // Write 8 LSB to Timer1

    TMR1IF = 0; // Clear interrupt status for Timer1

    TMR1IP = 1; // 1 = Set high priority interrupt for Timer1
    TMR1IE = 1; // 1 = Enables the Timer1 overflow interrupt
}