References

1. 1.AVR130: Using the timers on tinyAVR and megaAVR devices
2. 2.AVR135: Using Timer Capture to Measure PWM Duty Cycle on tinyAVR and megaAVR devices
3. 3.AVR205: Frequency measurement made easy with Atmel tinyAVR and Atmel megaAVR
4. 4.AVR504: Migrating from ATtiny26 to ATtiny261/461/861