Is it possible to underclock my nRF51822 to save power?

[tyler]

I am working on an nRF51822 central BLE device. I am wondering if it is possible to lower the clock speed / underclock the device to save power? I know this will make it run slower, but it already is running quicker than it needs to yet it is eating up too much power.

[Turbo J]

if it is possible to lower the clock speed / underclock the device to save power

Nope. The oscillators are fixed frequency - so they can start up faster.

Modern µC are designed for low avarage power in what is called "race to idle". That means a significant power draw at high procressing speed - but only for a short active time and then switching to a low power idle state for the majority of time.

That is why you can run the NRF5x from a CR2032 (~10 mA current shorted) with a few >=10 µF reservouir capacitors.

[RK]

There's always plenty of idle time for the CPU, the radio does most of the work and the CPU only wakes up long enough to process. In general however BLE is power optimised for peripherals and centrals use more power. You can use the Nordic's Power Profiler to model power usage in different situations and give yourself a better answer to your own question.