--- a/hello.c	Thu Apr 03 18:49:02 2014 +0300
+++ b/hello.c	Thu Apr 03 18:49:18 2014 +0300
@@ -1,22 +1,116 @@
 #include <avr/io.h>
-#include <util/delay.h>
+#include "stdlib.h"
 
-#define false       0
-#define true        1
+#include <avr/interrupt.h>
 
-#define SBI(port, bit) do { port |= (1 << (bit)); } while (0)
-#define CBI(port, bit) do { port &= ~(1 << (bit)); } while (0)
+#define TIMER_FLAGS     GPIOR0
+#define TIMER1_BUSY     1
+
+/*
+ * Setup timers.
+ */
+void timer_init (void)
+{
+    TCCR1A = (
+            // OC1A output pin disconnected
+            0b00 << COM1A0
+            // OC1B output pin disconnected
+        |   0b00 << COM1B0
+            // no PWM
+        |   0b00 << WGM10
+    );
+    TCCR1B = (
+            // CTC mode
+            0b01 << WGM12 
+    );
+    TCCR1C = 0;
+}
+
+void timer1_start (short cycles)
+{
+    // count up from zero...
+    TCNT1 = 0;
+
+    // ...to the given number of timer cycles
+    OCR1A = cycles;
+
+    // start!
+    sbi(&TIMER_FLAGS, TIMER1_BUSY);
+    TIMSK1 = (
+            // OCA interrupt
+            0b1 << OCIE1A       // enable
+    );
+    TCCR1B = (
+            // WGM
+            0b01  << WGM12      // CTC
+
+            // clocksource
+        |   0b101 << CS10       // 1024'th
+    );
+}
+
+static void timer1_stop ()
+{
+    // WGM: normal
+    // clocksource: stop
+    TCCR1B = 0;
+
+    cbi(&TIMER_FLAGS, TIMER1_BUSY);
+}
+
+ISR(TIMER1_COMPA_vect)
+{
+    timer1_stop();
+
+    // XXX: cpu will automatically wake up from sleep()
+}
+
+/*
+ * Sleep on timer1 interrupt.
+ */
+void timer_sleep (int cycles)
+{
+    // set timer
+    timer1_start(cycles);
+
+    // sleep
+    // TODO: PRR
+    SMCR = (
+            // idle sleep
+            (0b00 << SM0)
+
+            // enable sleep
+        |   (0b1 << SE)
+    );
+    
+    // sleep
+    while (tbi(&TIMER_FLAGS, TIMER1_BUSY)) {
+        __asm__ ( "sleep" :: );
+    }
+
+    // cleanup
+    SMCR = 0;
+}
 
 int main (void)
 {
+    timer_init();
+
     // LED
-    SBI(DDRB, DDB5);
+    sbi(&DDRB, DDB5);
+
+    sei();
+
+    // blink
+    short timeout = 1000;
+    short delta = 10;
 
     while (true) {
-        // flip
-        PORTB ^= (1 << PORTB5);
+        // bitflip
+        xbi(&PORTB, PORTB5);
         
-        // busyloop
-        _delay_ms(1000);
+        timer_sleep(timeout);
+        
+        timeout += delta;
     }
 }

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/stdlib.h	Thu Apr 03 18:49:18 2014 +0300
@@ -0,0 +1,32 @@
+#include <util/delay.h>
+
+#define false       0
+#define true        1
+
+typedef volatile uint8_t ioport_t;
+
+static inline ioport_t tbi(ioport_t *port, int bit)
+{
+    return *port & (1 << bit);
+}
+
+static inline void sbi(ioport_t *port, int bit)
+{
+    *port |= (1 << bit);
+}
+
+static inline void cbi(ioport_t *port, int bit)
+{
+    *port &= ~(1 << bit);
+}
+
+static inline void xbi(ioport_t *port, int bit)
+{
+    *port ^= (1 << bit);
+}
+
+void delay_1s ()
+{
+    // busyloop
+    _delay_ms(1000);
+}