/* Exercise 6.2 Mystic LCD    */
/* 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

#include "lcdlib.h"

unsigned char seed = 1 ;        //Variables associated with random number generation
unsigned char mask = 12 ;


//LFSR based algorithm for random number generation
//exclusive or bit 4 with bit 7, shift the seed and add the new bit
unsigned char random ( void )
{
    unsigned char top, mid ;

    if ( seed & mask )      //get new input bit
    {
        mid = 1 ;
    }
    else
    {
        mid = 0 ;
    }

    if ( seed & 0x80 )
    {
        top = 1 ;
    }
    else
    {
        top = 0 ;
    }

    seed = ( seed << 1 ) | ( mid ^ top ) ;

    return seed ;
}


void flicker ( void )
{
    unsigned char r = random ();
    lcd_cursor ( r % 16, r / 128 );
    lcd_print_ch ( ' ' + random () %98 );
}


int main (void)
{
    ANSELB = 0x00;              //Put PORTB into Digital mode, defaults to analogue
    OPTION_REG = 0xC0;

    lcd_start ();

    while (1)                   //Loop forever
    {
        flicker();
    }

    return 0;
}