/* Exercise 1.8 Flash one LED with a variable delay function */
/* Created David Miles April 2006 */
/* Updated Ben Rowland Febuary 2014 */

#include <xc.h>

// CONFIG1
#pragma config FOSC = HS        // Oscillator Selection (HS Oscillator, High-speed crystal/resonator connected between OSC1 and OSC2 pins)
#pragma config WDTE = OFF       // Watchdog Timer Enable (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable (PWRT disabled)
#pragma config MCLRE = ON       // MCLR Pin Function Select (MCLR/VPP pin function is MCLR)
#pragma config CP = OFF         // Flash Program Memory Code Protection (Program memory code protection is disabled)
#pragma config CPD = OFF        // Data Memory Code Protection (Data memory code protection is disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable (Brown-out Reset enabled)
#pragma config CLKOUTEN = OFF   // Clock Out Enable (CLKOUT function is disabled. I/O or oscillator function on the CLKOUT pin)
#pragma config IESO = OFF       // Internal/External Switchover (Internal/External Switchover mode is disabled)
#pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable (Fail-Safe Clock Monitor is disabled)

// CONFIG2
#pragma config WRT = OFF        // Flash Memory Self-Write Protection (Write protection off)
#pragma config VCAPEN = OFF     // Voltage Regulator Capacitor Enable (All VCAP pin functionality is disabled)
#pragma config PLLEN = OFF      // PLL Enable (4x PLL disabled)
#pragma config STVREN = ON      // Stack Overflow/Underflow Reset Enable (Stack Overflow or Underflow will cause a Reset)
#pragma config BORV = LO        // Brown-out Reset Voltage Selection (Brown-out Reset Voltage (Vbor), low trip point selected.)
#pragma config LVP = OFF        // Low-Voltage Programming Enable (High-voltage on MCLR/VPP must be used for programming)

#define _XTAL_FREQ 19660800	// Defines the hardware crystal frequency allowing the delay function to work correctly


/*  use #define to set up constants  */
#define UPPER_LIMIT 24000
#define LOWER_LIMIT 500
#define STEP 200


void delay ( unsigned int size );       //Function prototype


void delay ( unsigned int size )        //Function header
{
    unsigned int i ;                    //Temporary counter for delay
    for ( i=0 ; i < size ; i= i + 1 ) ; //Loop to perform delay
}


int main (void)
{
    unsigned int speed = LOWER_LIMIT ;  //speed counter
    char going_up = 1 ;                 //count direction

    ANSELA = 0x00;              //Set PORTA to Digital Mode - Defaults to analogue mode
    OPTION_REG = 0xC0;
    TRISA = 0xFE;               //Set bits 0 and 1 of PORTA to be configured as an output

    while (1)                   //Loop forever
    {
        LATA = 0x1;             //Set bit 0 of PORTA to output a logic 1, all other PORTA pins are 0

        delay( speed );         //Wait here for a number of milliseconds

        LATA = 0x0;             //Set bit 1 of PORTA to output a logic 1, all other PORTA pins are 0

        delay( speed );         //Wait here for a number of milliseconds

        if (going_up == 1)      //Are we ramping the delay up?
        {
            speed = speed + STEP;       //Increase delay variable
            if (speed >= UPPER_LIMIT)   //Check to see if we have reached or gone over the limit
            {
                going_up = 0;           //Change to be going down
            }
        }
        else                    //Otherwise were ramping down
        {
            speed = speed - STEP;       //Decrease delay variable
            if (speed <= LOWER_LIMIT)   //Check to see if we have reached or below the limit
            {
                going_up = 1;           //Change to be going up
            }
        }
    }

    return 0;
}