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#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include <avr/wdt.h>
#include <util/delay.h>
#include <stdlib.h>
volatile uint8_t disp[32];
int main (void)
{
// disable ADC to save power
power_adc_disable();
// dito
wdt_disable();
// Ports B and D drive the dot matrix display -> set all as output
DDRB = 0xff;
DDRD = 0xff;
PORTB = 0;
PORTD = 0;
// Enable 8bit counter with prescaler=8 (-> timer frequency = 1MHz)
TCCR0A = _BV(CS01);
// raise timer interrupt on counter overflow (-> interrupt frequency = ~4kHz)
TIMSK0 = _BV(TOIE0);
// smile!
disp[0] = 0x08;
disp[1] = 0x04;
disp[2] = 0x62;
disp[3] = 0x02;
disp[4] = 0x02;
disp[5] = 0x62;
disp[6] = 0x04;
disp[7] = 0x08;
disp[8] = 0x00;
disp[9] = 0x00;
disp[10] = 0x00;
disp[11] = 0x00;
disp[12] = 0x00;
disp[13] = 0x00;
disp[14] = 0x00;
disp[15] = 0x00;
disp[16] = 0x28;
disp[17] = 0x44;
disp[18] = 0x22;
disp[19] = 0x02;
disp[20] = 0x02;
disp[21] = 0x22;
disp[22] = 0x44;
disp[23] = 0x28;
disp[24] = 0x00;
disp[25] = 0x00;
disp[26] = 0x00;
disp[27] = 0x00;
disp[28] = 0x00;
disp[29] = 0x00;
disp[30] = 0x00;
disp[31] = 0x00;
sei();
while (1) {
// nothing to do here, go to sleep to save power
sleep_enable();
sleep_cpu();
}
return 0;
}
/*
* Draws a single display column. This function should be called at least once
* per millisecond.
*
* Current configuration:
* Called every 256 microseconds. The whole display is refreshed every 2048us,
* giving a refresh rate of ~500Hz
*/
ISR(TIMER0_OVF_vect)
{
static uint8_t active_col = 0;
static uint16_t scroll = 0;
static uint8_t disp_offset = 0;
uint8_t buffer_col;
if (++scroll == 256) {
scroll = 0;
if (++disp_offset == sizeof(disp)) {
disp_offset = 0;
}
}
buffer_col = (disp_offset + active_col) % sizeof(disp);
/*
* To avoid flickering, do not put any code (or expensive index
* calculations) between the following three lines.
*/
PORTB = 0;
PORTD = ~disp[buffer_col];
PORTB = _BV(active_col);
if (++active_col == 8)
active_col = 0;
}
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