From c36d0f8e4effb9cfd6c1c1b1f792aa4178d55c16 Mon Sep 17 00:00:00 2001
From: John Van Enk <vanenkj@gmail.com>
Date: Tue, 11 Oct 2011 00:13:13 -0400
Subject: [PATCH] 1 second blink example done with timers now.

---
 README         |  5 ---
 include/main.h | 14 +++++++++
 src/main.c     | 83 +++++++++++++++++++++++++++++++++++---------------
 3 files changed, 73 insertions(+), 29 deletions(-)
 create mode 100644 include/main.h

diff --git a/README b/README
index 5664d94..70ac22d 100644
--- a/README
+++ b/README
@@ -1,8 +1,3 @@
-The easy-to-read examples provided on the following site were a big help in setting
-this up quickly. The blink program originally used in src/main.c was borrowed from
-this page.
-  http://balau82.wordpress.com/2011/03/29/programming-arduino-uno-in-pure-c/
-
 Usage:
 
 $ rake -T # see all tasks
diff --git a/include/main.h b/include/main.h
new file mode 100644
index 0000000..bdf0084
--- /dev/null
+++ b/include/main.h
@@ -0,0 +1,14 @@
+#ifndef __MAIN_H__
+#define __MAIN_H__
+
+/* Assuming a clock rate of 16Mhz and a CLK/64 prescaler,
+ * we will see 250 ticks per millisecond. If we want to
+ * have the timer overlow ever millisecond, we need to
+ * initialize the counter to 5 after each tick. */
+#define TIMER_RESET_VAL 5
+
+void configure(void);
+void task(void);
+int main(void);
+
+#endif /* __MAIN_H__ */
diff --git a/src/main.c b/src/main.c
index e50f611..924771f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,30 +1,65 @@
-/*
- * This example was borrowed from:
- *   http://balau82.wordpress.com/2011/03/29/programming-arduino-uno-in-pure-c/
- */
-
 #include <avr/io.h>
-#include <util/delay.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+
+#include "main.h"
+
+int main(void)
+{
+  configure();
+
+  while(1) {;}
+
+  return 0;
+}
+
+void configure(void)
+{
+  /* disable interrupts */
+  cli();
+
+  /* configure TIMER0 to use the CLK/64 prescaler. */
+  TCCR0B = _BV(CS00) | _BV(CS01);
+
+  /* enable the TIMER0 overflow interrupt */
+  TIMSK0 = _BV(TOIE0);
 
-enum {
-	BLINK_DELAY_MS = 1000,
-};
+  /* set the initial timer counter value. */
+  TCNT0 = TIMER_RESET_VAL;
+
+  /* confiure PB5 as an output. */
+  DDRB |= _BV(DDB5);
+
+  /* turn off surface mount LED on */
+  PORTB &= ~_BV(PORTB5);
+
+  /* enable interrupts. */
+  sei();
+}
+
+void task(void)
+{
+  static uint16_t tick = 0;
+
+  /* toggle every thousand ticks */
+  if (tick >= 1000)
+  {
+    /* toggle the LED */
+    PORTB ^= _BV(PORTB5);
+
+    /* reset the tick */
+    tick = 0;
+  }
+
+  tick++;
+}
 
-int main (void)
+ISR(TIMER0_OVF_vect)
 {
-	/* set pin 5 of PORTB for output*/
-	DDRB |= _BV(DDB5);
-
-	while(1) {
-		/* set pin 5 high to turn led on */
-		PORTB |= _BV(PORTB5);
-		_delay_ms(BLINK_DELAY_MS);
-		
-		/* set pin 5 low to turn led off */
-		PORTB &= ~_BV(PORTB5);
-		_delay_ms(BLINK_DELAY_MS);
-	}
-
-	return 0;
+  /* preload the timer. */
+  TCNT0 = TIMER_RESET_VAL;
+  
+  /* call our periodic task. */
+  task();
 }