/* Exercise 6.4 Message test    */
/* 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

#define SPEED 400               // Used to trim the delay loops

#include "lcdlib.h"

const unsigned char messages [] =
{
    'n','o','*',
    'y','e','s','*',
    'p','r','o','b','a','b','l','y','*',
    'n','e','v','e','r','*',
    'n','o','t',' ','l','i','k','e','l','y','*',
    'n','o','t',' ','t','o','d','a','y','*',
    'u','n','c','l','e','a','r','*',
    'd','o','n','t',' ','b','e','t',' ','o','n',' ','i','t','*',
    'p','e','r','h','a','p','s','*',
    'o','u','t','l','o','o','k',' ','h','a','z','y','*',
    'a','s','k',' ','a','g','a','i','n','*',
    'i','t',' ','d','e','p','e','n','d','s','*',
    0x00
};


const unsigned char banner1 [] = {'*','*','*','M','y','s','t','i', 'c', ' ','L','C','D','*','*','*',0x00} ; 
const unsigned char banner2 [] = {'*','*','P','r','e','s','s',' ','t','o',' ','a','s','k','*','*',0x00} ;

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


//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 & 12 )      //get new input bit
    {
        mid = 1 ;
    }
    else
    {
        mid = 0 ;
    }

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

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

    return seed ;
}


//#define DEBUG

void show_message ( unsigned char number )
{
    int pos = 0 ;

    while (number > 0)                      //find the start of the message
    {
        #ifdef DEBUG
          lcd_print_ch ( messages [pos] ) ;
        #endif

        if (messages [pos] == '*')
        {
            number = number - 1 ;
        }
        pos = pos + 1 ;                     //This is the line which is missing in the previous version
    }

    while ( messages [pos] != '*' )         //print the message
    {
        lcd_print_ch ( messages [pos] ) ;
        pos = pos + 1 ;
    }
}


void flicker ( void ) 
{
    unsigned char r = random () ;
    lcd_cursor ( r % 16, r / 128 ) ;
    lcd_print_ch ( 'A' + random () % 26 ) ;
}


//counts the messages in the message string, returns the result as a an integer
unsigned char count_messages ( void )
{
    unsigned char i, count = 0 ;

    for (i = 0; messages[i] != 0; i = i + 1 )
    {
        if (messages[i] == '*')
        {
            count = count + 1;
        }
    }
    return count;
}


void big_delay ( int size )
{
    int i, j ;
    for (i = 0; i < size; i = i + 1 )
    {
        for (j = 0; j < SPEED; j = j + 1);
    }
}


void setup_hardware (void)
{
    ANSELA = 0x00;              //Put PORTA into Digital mode, defaults to analogue
    ANSELB = 0x00;              //Put PORTB into Digital mode, defaults to analogue
    OPTION_REG = 0xC0;
    TRISA = 0x01 ;              //bit 0 of PORTA for input everything else is output
}


//returns the debounced state of the bottom bit of PORTA
unsigned char key ( void )
{
    unsigned char count = 0;
    unsigned char oldv, newv;

    oldv = PORTA & 0x01 ;

    while (count < 20)
    {
        newv = PORTA & 0x01 ;
        if (oldv == newv)
        {
            count++ ;
        }
        else
        {
            count = 0 ;
            oldv = newv ;
        }
    }
    return oldv ;
}


int main (void)
{
    unsigned char i, lim;
    
    setup_hardware();

    lcd_start ();

    lim = count_messages () ;

    while (1)                   //Loop forever
    {
        lcd_clear () ;
        lcd_print ( banner1 ) ;
        lcd_cursor ( 0, 1 ) ;
        lcd_print ( banner2 ) ;

        while ( key() == 0 ) random ();     //wait for keypress

        while ( key () == 1 ) flicker ();   //wait for key up

        lcd_clear ();
        show_message ( random () % lim );
        big_delay ( 3000 );
    }

    return 0;
}