stars.c

//----------------------------------------------------------------------------------------------
//
// starsII
//
// Ver 0.1 - written in sourceboost c for the 16F628
//
// Author : MrTrick
// Date : 2010-12-25
// License : GPLv2
//
// Description :
// * Sits in sleep mode until the button is pressed. (connected to MCLR)
// * Turns the background and foreground stars on.
// * Flickers the foreground stars occasionally.
// * Goes back to sleep after a period of time, or if the button is pressed again.
// 
//----------------------------------------------------------------------------------------------
//#define TESTING

#include "system.h"
#include "rand.h"
#ifdef TESTING
	#pragma DATA _CONFIG, _BODEN_OFF & _PWRTE_ON & _WDT_OFF & _LVP_OFF & _MCLRE_OFF & _INTRC_OSC_NOCLKOUT
#else
	#pragma DATA _CONFIG, _BODEN_OFF & _PWRTE_ON & _WDT_OFF & _LVP_OFF & _MCLRE_ON & _INTRC_OSC_NOCLKOUT
#endif
#pragma CLOCK_FREQ 4000000
typedef unsigned char byte;

//The number of increments above 'normal' that a star increases in brightness
#define TWINKLE 70

//How many cycles will be run before the field switches off?
#define ON_CYCLES 28000 // About 10 minutes

//----------------------------------------------------------------------------------------------
// Variables
//----------------------------------------------------------------------------------------------

volatile bit background				@PORTA.1;
volatile bit background_dir			@TRISA.1;
volatile byte stars_port			@PORTB;
volatile byte stars_dir				@TRISB;

byte brightness[20];
byte i;
byte compare[4]						@0x70; //Force into shared space
unsigned short cycles;

void init() {
	// Random!
	srand(1234);

	// I/O - Initially all inputs
	stars_dir = 0b11111111;
	background_dir = 1;

	// What should the device do?
#ifndef TESTING
	//  If it was RESET while in the middle of displaying, (PD will be set) switch it off.
	if (test_bit(status, NOT_PD))
		sleep();
	//  If it was RESET while in sleep, (PD will be cleared) start it.
	else
		clear_wdt(); //Set PD
#endif

	//Run for a specific amount of time
	cycles = ON_CYCLES;
}

void pulseBank() 
{
	//Minimum brightness per star	
	delay_100us(20); 
	//Switch off each star as the brightness reaches zero.
	i=TWINKLE+1;
	while(i--) {
		if (!compare[0]) set_bit(stars_dir,7); compare[0]--;
		if (!compare[1]) set_bit(stars_dir,6); compare[1]--;
		if (!compare[2]) set_bit(stars_dir,5); compare[2]--;
		if (!compare[3]) set_bit(stars_dir,4); compare[3]--;
	}
}

void main() {
	//Initialise, and decide whether to run the cycles or halt.
	init();

	//Run!
	background_dir = 0;
	background = 1;
	while(--cycles) 
	{
#ifndef TESTING
		//Sometimes twinkle a random star
		byte x = rand() >> 8;
		if (x < 20) brightness[x] = TWINKLE;
#endif

		//Dim any brighter stars by one
		asm {
			movlw _brightness 	; Load the start address into fsr
			movwf _fsr

			loop:
			movf _indf, W			; Decrement the star if it is brighter
			btfss _status, Z
			decf _indf, F
						
			incf _fsr, F			; Go to the next star, stop if done
			movlw _brightness+20
			xorwf _fsr, W
			btfss _status, Z
			goto loop
		}

		//Display Bank 0's stars
		compare[0] = brightness[0];	
		compare[1] = brightness[1];
		compare[2] = brightness[2];
		compare[3] = brightness[3];
		stars_port = 0b11110000;
		stars_dir  = 0b00001101; // 7654 out, 1 in.
		pulseBank();
					
		//Display Bank 1's stars
		compare[0] = brightness[4];	
		compare[1] = brightness[5];
		compare[2] = brightness[6];
		compare[3] = brightness[7];
		stars_port 	= 0b00001000;
		stars_dir 	= 0b00000111; // 3 out, 7654 in.
		pulseBank();

		//Display Bank 2's stars
		compare[0] = brightness[8];	
		compare[1] = brightness[9];
		compare[2] = brightness[10];
		compare[3] = brightness[11];
		stars_port 	= 0b00000100;
		stars_dir 	= 0b00001011; // 2 out, 7654 in.
		pulseBank();

		//Display Bank 3's stars
		compare[0] = brightness[12];	
		compare[1] = brightness[13];
		compare[2] = brightness[14];
		compare[3] = brightness[15];
		stars_port 	= 0b00000010;
		stars_dir 	= 0b00001101; // 1 out, 7654 in.
		pulseBank();

		//Display Bank 4's stars
		compare[0] = brightness[16];	
		compare[1] = brightness[17];
		compare[2] = brightness[18];
		compare[3] = brightness[19];
		stars_port 	= 0b00000001;
		stars_dir 	= 0b00001110; // 0 out, 7654 in.
		pulseBank();
	}

	//Switch off the stars and go to sleep. (until reset again) Goodnight!
	stars_dir = 0b11111111;
	background_dir = 1;
	sleep();
}