/* Exercise 6.1 Random number workout  */
/* 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 = 55 ;       //Variables associated with random number generation
unsigned char mask = 1 ;


//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 display_value ( int value )
{
    unsigned char hunds, tens, units ;

    //First get the digits
    units = value % 10;
    value = value / 10;
    tens = value % 10;
    value = value / 10;
    hunds = value % 10;

    //Now display them
    lcd_print_ch ('0' + hunds);
    lcd_print_ch ('0' + tens);
    lcd_print_ch ('0' + units);
}


int main (void)
{
    int cyclesize = 0;          //counter variables
    int cyclemax = 0;
    int i;

    int winstart = 0;           //winning values
    int winmask = 0;

    ANSELB = 0x00;              //Put PORTB into Digital mode, defaults to analogue
    OPTION_REG = 0xC0;

    lcd_start ();

    for (mask = 1; mask < 128; mask = mask + 1 )    //for each possible mask value
    {

        lcd_cursor ( 0, 0 );
        display_value ( mask );                     //show what we are working on

        for ( i=0 ; i < 255 ; i++ )                 //try each seed in turn
        {
            seed = i;
            cyclesize = 0;                          //clear the cycle counter

            while (random () != i)                  //get random numbers until we end up back where we started
            {
                cyclesize++;
            }

            if (cyclesize > cyclemax)               //if we have a new largest cycle we store the values which created it
            {
                winstart = i;
                winmask = mask;
                cyclemax = cyclesize;
            }
        }
    }

    lcd_cursor (0, 0);

    display_value (winmask);                        //display the results
    lcd_print_ch ( ' ' );

    display_value (winstart);
    lcd_print_ch ( ' ' );

    display_value (cyclemax);

    while (1)                   //Loop forever
    {
    }

    return 0;
}