In this demo we show how we can change the ATtiny85 clock speed on the fly by modifying the prescaler. We note that using _delay_ms() is subject to the F_CPU and if we double the MHz we need to double _delay_ms() in order for the timing to be correct. Changing the clock speed on the fly may be useful for power saving applications where there might be brief moments to increase the clock speed, e.g. communicating with devices like USB.
Download the code: ATtiny85_CPU_Speed_v1.0