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Mastering Embedded Linux Development
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If running for a kilometer takes more energy than walking, then maybe running the CPU at a lower frequency can save energy. Let’s see.
The power consumption of a CPU when executing code is the sum of a static component, caused primarily by gate leakage current, and a dynamic component, caused by the gate switching:
Pcpu = Pstatic + Pdyn
The dynamic power component is dependent on the total capacitance of the logic gates being switched, the clock frequency, and the square of the voltage:
Pdyn = CFV2
Changing the frequency by itself does not save energy because the same number of CPU cycles need to be completed for a given task. If we reduce the frequency by half while keeping the voltage constant, then it will take twice as long to complete the task, even though the total amount of energy expended is the same. In fact, reducing the frequency may actually increase the power budget because it takes longer for the CPU to enter an...