If you want to reduce the power consumption of the MCU, it is common to design the software so that it operates intermittently. Intermittent operation refers to a series of processes such as shifting to sleep mode when necessary processing is completed, periodically returning to operating mode (waking up) to perform processing, and then shifting to sleep mode again after processing is completed. It works. By remaining in sleep, deep sleep, or standby modes with low power consumption during periods when the MCU is not processing, the average power consumption can be reduced.

Current consumption during operation mode (run mode, active mode) is called active current. The name differs for each MCU manufacturer. The active current is defined in units such as ○○mA at △△MHz or ○○mA/MHz, depending on the operating frequency used. By using an MCU with excellent specifications (low current consumption), the average power consumption can be reduced.

Then, should we choose an MCU with excellent specs? Well, it's not that simple.
Since the instruction efficiency differs depending on the CPU core used, even if the current consumption is a little high, using a CPU core with high instruction efficiency to complete processing in a short time will result in lower power consumption overall. You might. Cortex-M is a CPU with very good instruction efficiency, so it tends to complete processing in about 1/1.3 to 1/4 clock cycles compared to general 8/16-bit MCUs.
Also, since there are no particular preconditions for specifying the specifications, the power consumption value when executing NOP, the current consumption value when fetching flash, etc. are used. I think. The most reliable way to make an accurate comparison is to measure on the actual machine.

If the CPU is awake and doing work for very short periods of time, but stays in sleep/standby mode for long periods of time, the active current will not have much effect.
However, if the operating mode ratio is high, the active current has a large effect on the average current.

If you are aware of the frequency-current curve, you can also see the difference in the base current (offset value) and whether the frequency and current are proportional. ) will appear. The EFM32's low power mode specs are particularly good, so it tends to be better to use it at a high frequency to finish processing in a short time and stay in low power mode for as long as possible.