From 7ce050f2387c2276218a7c002d7631dd3edd0c72 Mon Sep 17 00:00:00 2001
From: Daniel Friesel <derf@finalrewind.org>
Date: Tue, 12 Jan 2016 13:02:17 +0100
Subject: add display render loop and example image

---
 main.c | 43 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 11 deletions(-)

diff --git a/main.c b/main.c
index 1911237..0529721 100644
--- a/main.c
+++ b/main.c
@@ -1,11 +1,14 @@
 #include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
 #include <avr/wdt.h>
 #include <util/delay.h>
 #include <stdlib.h>
 
+volatile uint8_t disp[8];
+
 int main (void)
 {
-	unsigned int i, j, h;
 	wdt_disable();
 
 	DDRB = 0xff;
@@ -14,18 +17,36 @@ int main (void)
 	PORTB = 0;
 	PORTD = 0;
 
+	TCCR0A = _BV(CS00); // no prescaler (/8 without software prescaler is okay too)
+	TIMSK0 = _BV(TOIE0); // interrupt on overflow
+
+	// 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;
+
+	sei();
+
 	while (1) {
-		for (i = 1; i < 256; i *= 2) {
-			PORTB = i;
-			for (j = 1; j < 256; j *= 2) {
-				PORTD = ~j;
-				for (h = 1; h < 1; h++) { // use "h < 4096" for visible pixels (e.g. finding soldering errors)
-					asm("nop");
-				}
-			}
-			PORTB = 0;
-		}
+		sleep_enable();
 	}
 
 	return 0;
 }
+
+ISR(TIMER0_OVF_vect)
+{
+	static uint8_t active_col = 0;
+
+	PORTB = 0;
+	PORTD = ~disp[active_col];
+	PORTB = _BV(active_col);
+
+	if (++active_col == 8)
+		active_col = 0;
+}
-- 
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