Question regarding HFCLK control

[hjjeon]

Dear Nordic guy, I'm developing with nrf51822(6.0 stack binary and 5.0 sdk) I have one question regarding clock. As I know,automatically,stack go to the sleep mode(HF clock disable)and wakup. but,we have some problem,So,we have a plan to estimate a sleep current consumption, using a NRF_CLOCK->TASKS_HFCLKSTART and NRF_CLOCK->TASKS_HFCLKSTOP manually at the application code due to 32k clock rtc timer. For just estimation purpose not apply to product case. Can I use the NRF_CLOCK->TASKS_HFCLKSTART and NRF_CLOCK->TASKS_HFCLKSTOP ? Is it possible?

[Stefan Birnir Sverrisson]

Hi hjjeon

Have you looked at this thread and this thread. As explained in those threads, the BLE softdevice needs both 16MHz HFCLK source and 32kHz LFCLK clock source. For BLE operation, 16MHz 40ppm crystal is required as well as 500ppm 32kHz low frequency clock. For CPU and peripheral operation, internal 16MHz RC is sufficient.

You might also benefit of looking at this thread, scroll down to the section "Choice of 32 kHz clock source" which is most relevant.

The BLE softdevice automatically controls the HFCLK and LFCLK sources and only enables them when needed. The external HFCLK crystal is only enabled during a BLE event, i.e. when the radio is active. In between radio events, the nRF51 is in System On low power mode, where only the LFCLK is active and the RTC0. You should expect to see around 3,5uA current consumption in between radio events.

So if you have the S110 softdevice enabled, you should not need to trigger any clock task, it is already taken care of by the softdevice.

[Steph van Schalkwyk]

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[Sigurd]

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