Application core

[Tom Chiang]

128 MHz or 64 MHz operation is mentioned in the specification (page ii). However, can MCU be capped at around 12MHz? How about the current consumption?

[Turbo J]

Tom Chiang said:

MCU be capped at around 12MHz?

Nope.

On light loads, the MCU consumes less current with short runs at full clock and longer pauses with the clock shut down.

[Tom Chiang]

Dear Turbo:

Thanks for replying.

Is capped at around 12MHz an example of short runs at full clock? If it is, how much is the current consumption?

[Vidar Berg]

You can either select 64MHz or 128Mhz on the app core. Other frequencies are not supported. But as Turbo already pointed out, a lower CPU frequency doesn't automatically guarantee a lower power consumption. A higher frequency may allow the system to spend less of its time executing code and more of its time in sleep.

[Tom Chiang]

Dear Vidar:

Thanks for replying.

I think as you said to allow the system to spend less of its time executing code and more of its time in sleep means to make the system be in an idle or run state periodically, right? How can we do this?

The description in specification 4.1 System ON mode is "depending on the configuration set by the software and the state of the executing application". Any method or step in more detail referring to your experience?

Furthermore, can I calculate the current consumption while doing so? After all, a decrease in power consumption is all we need. 

[Vidar Berg]

Hello,

Zephyr enters an idle thread that puts the device in System ON mode automatically when there is nothing else to do, so you as the app developer can focus on optimizing the application code (i.e. reduce execution time).

Tom Chiang said:

Furthermore, can I calculate the current consumption while doing so? After all, a decrease in power consumption is all we need. 

To make an estimate you first have to determine how much time is spent executing code and how much is spent in sleep. Segger SystemViewer is a tool which may help you visualize this. 

Typical system CPU and sleep run currents can be found in the product specification here: Current consumption

Edit: I would also recommend you take a look at the Power optimization section of the Application development chapter in the NCS documentation.