/*
 * digidie.c
 *
 * A digital die.  A random number between 1 and 6 is displayed
 * on a 7-segment display when a button is pressed and also for a
 * few seconds after the button is released.  Otherwise a rotating
 * pattern is displayed.  If there have been no button presses
 * for around 30 seconds the processor goes to sleep but will wake
 * again when the button is pressed.  A random number generator isn't
 * used; the randomness arises from the uncertainty in the time
 * the button is pressed relative to the state of an internal timer.
 *
 * The program can be used to try out the PIC C compiler from HI-TECH
 * Software (a time-limited demo is available: http://www.htsoft.com).
 * Compile for the 16F84 using full optimization.
 *
 * The digital die can use either the 16C84 or 16F84 and was designed
 * to be programmed in-circuit using very simple hardware (see:
 * http://www.man.ac.uk/~mbhstdj/icp84.html for more details).  A
 * common anode 7-segment LED display is attached to the PIC via
 * 470 ohm resistors as follows:
 *
 *    RA0 segment a
 *    RA1 segment b
 *    RA2 segment c
 *    RA3 segment d
 *    RA4 segment e
 *    RB4 segment f
 *    RB5 segment g
 *
 * The common connection goes to VDD.  A normally open switch is
 * connected from RB7 to GND via a 470 ohm resistor.  The PIC
 * configuration word is set for a crystal oscillator (the Xtal 
 * frequency should be communicated to the program via the FREQ
 * macro below).
 *
 * Copyright (C) 1998 David Tait (david.tait@man.ac.uk)
 *
 */

#include <pic.h>
 
#define FREQ    3579454.                // crystal frequency in Hz
// #define FREQ    4000000.
#define TICKSIZ (1024./FREQ)
#define SECS(x) ((unsigned)((x)/TICKSIZ))
#define WAIT()  do delay(SECS(0.1)); while ( button == 0 )
#define SLEEP() asm("\tsleep")   
	

typedef unsigned char BYTE;

bit volatile button @ (unsigned) &PORTB*8+7;    // button on RB7

BYTE volatile pressed;          // set by button press interrupt
BYTE volatile number;           // a number grabbed from TMR0

const BYTE segtab[10] =         // convert digit to segment form
{
    0x40, 0x79, 0x24, 0x30, 0x19,       // only entries 1 to 6 used here
    0x12, 0x02, 0x78, 0x00, 0x10         
};



void interrupt grab_timer(void)         // grab TMR0 when button pressed
{
    if ( button == 0 && !pressed ) {
	number = TMR0;
	pressed = 1;
    }
    RBIF = 0;
}

     
void display(BYTE segs)
{
    PORTA = segs;
    PORTB = (segs>>1)&0x30;
}


void delay(unsigned ticks)      // waste time in ticks (256us @ 4MHz)
{
    while ( ticks-- ) {
	T0IF = 0;
	while ( T0IF == 0 )
	    continue;
    }
}


void roll(void)                 // display a rotating pattern
{
    unsigned i = 0;
    BYTE segs = 1;

    pressed = 0;
    for (;;) {
	display(~segs);
	delay(SECS(.05));
	if ( (segs <<= 1) == 0x40 )
	    segs = 1;
	if ( ++i > 600 ) {      // power-down after 30 secs
	    i = 0;
	    display(0xFF);      // turn off all segments
	    SLEEP();            // sleep until button pressed
	    WAIT();             // wait for button release
	    pressed = 0;        // and continue
	}
	if ( pressed )
	    break;              // return if button pressed
    }
}


BYTE mod6(BYTE n)               // compute n%6 without using library
{
    BYTE count, m6 = 6<<5;

    for ( count = 0; count < 6; ++count, m6 >>= 1)
	if ( n >= m6 )
	    n -= m6;
    return n;
}


void main(void)
{
    static BYTE bias = 0;       // used to ensure equal probabilities
    BYTE n;
    
    __CONFIG(0x3FF9);           // XT oscillator (and PWRTE if 16C84)

    TRISA = 0;                  // PORTA all outputs
    TRISB = 0x80;               // PORTB all outputs except RB7
    OPTION = 8;                 // enable weak pullups, TMR0 rate 1:1
    INTCON = 0x88;              // enable change on RB<4:7> interrupt
    
    for (;;) {
       if ( ++bias >= 6 )       // update bias
	   bias = 0;
       roll();                  // wait for a button press
       n = mod6(number);
       n = mod6(n + bias) + 1;
       display(segtab[n]);      // display die value
       WAIT();                  // wait for button release
       delay(SECS(3.0));        // hold display for 3 seconds
    } 
}