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-rw-r--r--main.c58
1 files changed, 46 insertions, 12 deletions
diff --git a/main.c b/main.c
index 736671c..369bc05 100644
--- a/main.c
+++ b/main.c
@@ -1,24 +1,32 @@
#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[16];
+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;
- TCCR0A = _BV(CS00); // no prescaler (/8 without software prescaler is okay too)
- TIMSK0 = _BV(TOIE0); // interrupt on overflow
+ // 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;
@@ -29,24 +37,50 @@ int main (void)
disp[5] = 0x62;
disp[6] = 0x04;
disp[7] = 0x08;
- disp[8] = 0x28;
- disp[9] = 0x44;
- disp[10] = 0x22;
- disp[11] = 0x02;
- disp[12] = 0x02;
- disp[13] = 0x22;
- disp[14] = 0x44;
- disp[15] = 0x28;
+ 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;
@@ -55,7 +89,7 @@ ISR(TIMER0_OVF_vect)
uint8_t buffer_col;
- if (++scroll == 1024) {
+ if (++scroll == 256) {
scroll = 0;
if (++disp_offset == sizeof(disp)) {
disp_offset = 0;