ATTiny LED Twinkler

main.c

/* ATTiny LED Twinkler
 * 
 * This is come code I wrote a while back to "twinkle"
 * four GPIO outputs that would drive LEDs. It was designed
 * to be run on an eight-pin ATTiny13 chip. It works
 * quite well, even considering how inefficient it is.
 *
 * - Robert Quattlebaum, 2012
 */

#include <avr/io.h>
#include <stdlib.h>
#include <string.h>
#include <avr/wdt.h>
#include <avr/interrupt.h>

#define sbi(x,y)	x|=(1<<y)
#define cbi(x,y)	x&=~(1<<y)

void delay_ms(uint8_t ms) {
	uint16_t delay_count = F_CPU / 17500;
	volatile uint16_t i;
	while(ms!=0) {
		for(i=0;i!=delay_count;i++);
		wdt_reset();
		ms--;
	}
}

#define LED0_on()	sbi(PORTB,0)
#define LED1_on()	sbi(PORTB,4)
#define LED2_on()	sbi(PORTB,3)
#define LED3_on()	sbi(PORTB,1)

#define LED0_off()	cbi(PORTB,0)
#define LED1_off()	cbi(PORTB,4)
#define LED2_off()	cbi(PORTB,3)
#define LED3_off()	cbi(PORTB,1)

uint8_t led0_v=200;
uint16_t led0_e;
uint16_t led1_v=200;
uint16_t led1_e;
uint16_t led2_v=200;
uint16_t led2_e;
uint16_t led3_v=200;
uint16_t led3_e;

#if 0
#define add_ret_c(x,y) (asm volatile (	\
		"clr __tmp_reg__\n"	\
		"add %0, %1\n"	\
		"adc __tmp_reg__, __zero_reg__\n"	\
		:	\
         "=r" (x),	\
		 "=r" (y)	\
    ),r0)
#else
uint16_t argh;
#define add_ret_c(x,y) ( argh=x, x+=y, argh<x )
#endif

void update_leds() {
	if(add_ret_c(led0_e,led0_v*led0_v))
		LED0_on();
	else
		LED0_off();
	if(add_ret_c(led1_e,led1_v*led1_v))
		LED1_on();
	else
		LED1_off();
	if(add_ret_c(led2_e,led2_v*led2_v))
		LED2_on();
	else
		LED2_off();
	if(add_ret_c(led3_e,led3_v*led3_v))
		LED3_on();
	else
		LED3_off();
}

ISR(TIM0_COMPA_vect) {
	update_leds();
}


uint8_t fastrand() {
	static uint8_t ret;
	ret*=97;
	ret+=101;
	return ret;
}

void main(void) {
	int i;

	// Stop the timer, if it happens to be running.
	TCCR0B = 0;
	OCR0A = 128;

	TCNT0 = 0; // Reset counter.

	// Start timer with prescaler of 1/8.
	TCCR0B = (1 << 1);
	sbi(TIMSK0, OCIE0A);

	// Enable interrupts.
	sei();

	// LED 0 = B0
	// LED 1 = B4
	// LED 2 = B3
	// LED 3 = B1

	sbi(DDRB,0);
	sbi(DDRB,4);
	sbi(DDRB,3);
	sbi(DDRB,1);


	uint8_t led0_t=fastrand();
	uint8_t led1_t=fastrand();
	uint8_t led2_t=fastrand();
	uint8_t led3_t=fastrand();

	led0_v=fastrand();
	led1_v=fastrand();
	led2_v=fastrand();
	led3_v=fastrand();

	while(1) {
		if(led0_t==led0_v) led0_t=fastrand();
		if(led1_t==led1_v) led1_t=fastrand();
		if(led2_t==led2_v) led2_t=fastrand();
		if(led3_t==led3_v) led3_t=fastrand();

		if(led0_t<led0_v) led0_v--;
		else led0_v++;
		if(led1_t<led1_v) led1_v--;
		else led1_v++;
		if(led2_t<led2_v) led2_v--;
		else led2_v++;
		if(led3_t<led3_v) led3_v--;
		else led3_v++;

		delay_ms(2);
	}
}