Underclocking PiZero for power saving worth it?

Question

How much power does the PiZero consume on it's lowest possible cpu clock setting (underclocked)? (Let's say the only usb add on is a wifi dongle.) And... is it worth it?

Answer 1

Underclocking modern ARM cores usually brings little benefit. While lower clock frequency (and perhaps lower core voltage) do reduce power consumption, a core clocked to the nominal frequency runs faster, meaning it spends less time in active state and more time in sleep, which is a more efficient* way of saving energy than permanently running underclocked.

I remember playing with clock settings on a Banana Pi under moderate load (video playback) and checking current consumption via /sys/class/power_supply/. Differences I observed were smaller than the measurement fluctuations.

(*) efficient in the sense that you still have full CPU performance available when you need it.

Answer 2

According to this forum post, fixing the CPU frequency at 600MHz (no more turboing to 1GHz) on a Pi Zero 2 W did save total consuming power:

With default settings, a 4-core prime number benchmark took 413 seconds to run, averaging 2.07W of power draw and in total consuming 0.237Wh of energy.

With the underclock and undervolt, it took 691 seconds to run, averaging 1.06W of power draw and in total consuming 0.204Wh of energy.

Thats an energy reduction of about 14%. It may be possible to do even better than this with a more aggressive undervolt.

These are the settings for the /boot/config.txt

arm_freq=600
arm_freq_min=600
over_voltage=-6
over_voltage_min=-6

WARNING: setting over_voltage and over_voltage_min to -8, disabled wlan0. Please caution while fiddling with these settings.

Answer 3

• power measurement chart of the Pi-Zero: less than the RaspPi A version. https://plus.google.com/post/z13wuzkavtb1f3hnc224ifgq4oehi1mmg