/* Exercise 4.6 Second Clock  */
/* 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


//A value for each bit in PORTA. We can feed in the number of the LED and it will give us the value to put into A
const unsigned char enable [4] = { 1, 2, 4, 8 } ;

//These are the patterns for the LEDs which were worked out from the datasheet.
//Note that to light a LED the bit on PORTB must be low I can use this array to convert from a digit to the 7 segments needed
const unsigned char patterns [10] = { 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x83, 0xf8, 0x80, 0x98 } ;
//                                      0     1     2     3     4     5     6     7     8     9

#define DISPLAY_SIZE 4          //Number of LEDs in our display

unsigned char segments [DISPLAY_SIZE] ;     //Segment patterns for our LEDs
unsigned char led_counter = 0 ;             //Counter used by our refresh
unsigned char counter = 0;                  //Timer interrupt counter

int count = 0;                              //Our counter value
int divisor = 0;                            //Interrupt divide count value


void setup_hardware (void)
{
    ANSELA = 0x00;              //Set PORTA to Digital Mode - Defaults to analogue mode
    ANSELB = 0x00;              //Set PORTB to Digital Mode - Defaults to analogue mode
    OPTION_REG = 0xC0;
    TRISA = 0xF0;               //Set bits 0-3 PORTA to be configured as an output
    TRISB = 0x00;               //Set all bits of PORTB to be configured as an output

    INTCON = 0b10100000;        //Configure INTCON register to enable timer interrupts
    OPTION_REG = 0b11000100;    //Configure the timer to use the prescaler 1:32 - 19660800 / 4 / 32 / 256 = 600Hz
}


//Each time refresh is called it sets the display for a led and moves on to the next
void refresh ( void )
{
    LATA = 0 ;                          //Turn off all the LEDS
    LATB = segments[led_counter];       //Set segments for the led
    LATA = enable[led_counter];         //Turn the led on
    led_counter = led_counter + 1 ;     //Move on to the next led

    if ( led_counter == DISPLAY_SIZE )  //see if we fell off the end
    {
        led_counter = 0 ;
    }
}


//Display just loads the pattern into the segment. refresh will read it later
void display ( unsigned char digit, unsigned char pos )
{
    segments[pos] = patterns[digit];
}


//TMR0 Overflow handler
void tmrHandler( void )
{
    refresh();
    divisor++;
    if (divisor == 20)    //update count every 10th of a second
    {
        count++;
        divisor = 0;
    }
}


//Allows a numeric variable to be printed to the 4 x 7-seg LEDs
void display_value ( int value )
{
  display ( value % 10, 3 ) ;   //display the units
  value = value / 10 ;

  display ( value % 10, 2 ) ;   //display the tens
  value = value / 10 ;

  display ( value % 10, 1 ) ;   //display the hundreds
  value = value / 10 ;

  display ( value % 10, 0 ) ;   //display the thousands
}


//This is the interrupt handler which is called when the PIC detects an interrupt
//It checks the status bits to find out who caused the interrupt and then calls that handler
void interrupt isr( void )
{
    if(INTCON & 0b00000100)                 //if the timer has overflowed bit 2 of INTCON is set high
    {
        INTCON = INTCON & 0b11111011;       //Clear bit 2 to turn off this interrupt
	counter = counter + 1;              //Increment interrupt counter

        if ( counter > 2 )                  //If counter is greater than 2
        {
            counter = 0;                    //Reset counter to 0
            tmrHandler();                   //Call the interrupt handler function
        }
    }
}



int main (void)
{
    setup_hardware();

    while (1)               //Loop forever
    {
        display_value (count);              //Send new count to LEDs
    }

    return 0;
}