Power consumption when changing HFCLK

RE: Power consumption when changing HFCLK

Kenneth — Mon, 07 Jun 2021 07:28:47 GMT

If you need an accurate HFCLK while the chip is running CPU, then you need to request and release the HFCLK while awake. However since the chip will wakeup frequent, and the time to startup the external HFCLK require 1.5ms, this will have a higher power consumption hit on average. My impression is that the majority of applications out there dont' do this (the don't start the external HFCLK), is there are particular reason why you need the external HFCLK while executing code?

Kenneth

RE: Power consumption when changing HFCLK

komuro — Fri, 04 Jun 2021 07:17:29 GMT

Thank you for your answer!

I used the softdevice api you gave me, but it didn't lower the power consumption.
I implemented the following after nrf_sdh_enable_request.

    uint32_t p_is_running = 0;

    sd_clock_hfclk_request();

    do {
        sd_clock_hfclk_is_running( &p_is_running );
    } while( p_is_running == 0);

Is there a problem with the above response?
If there is any other way to change the oscillator other than the above, please let me know.

Also, the following link says that the oscillator is automatically switched.
Does the external oscillator work without the above settings in the first place?
devzone.nordicsemi.com/.../nrf52832-external-hfxo

I have one more question to add.

If I use the software device API to switch to using an external oscillator instead of switching directly to using an external oscillator in the registers, will I still get more current?

RE: Power consumption when changing HFCLK

Kenneth — Thu, 03 Jun 2021 14:07:49 GMT

Hi,

You should not access some of the peripherals directly when softdevice is enabled, please see here:
https://infocenter.nordicsemi.com/topic/sds_s112/SDS/s1xx/sd_resource_reqs/hw_block_interrupt_vector.html

Instead you should use the softdevice api, for hfclk control you can find that here:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s112.api.v7.2.0/group___n_r_f___s_o_c___f_u_n_c_t_i_o_n_s.html#ga3e5afb495a1b0307c749cc268df94a74

When you are calling sd_app_evt_wait() this will stop the HFCLK (both internal and external), by default it will always startup using internal HFCLK after sleep. In your case you are manually starting the external HFCLK every time after sleep, this will take some time, and thereby increase average current consumption. Typically external HFCLK is only required when used by the radio due to the high accuracy, this is then handled by the softdevice automatically.

Kenneth