System Clock Frequency

RE: System Clock Frequency

bjorn-spockeli — Tue, 30 Jul 2019 08:23:34 GMT

Happy to help!

RE: System Clock Frequency

Jay_Shah — Tue, 30 Jul 2019 08:14:47 GMT

Thank you bjorn-spockeli it's clear now.

RE: System Clock Frequency

bjorn-spockeli — Tue, 30 Jul 2019 08:02:29 GMT

Correct.That is done by the HFCLK clock controller, which provides the following clocks to the system.

HCLK64M: 64 MHz CPU clock
PCLK1M: 1 MHz peripheral clock
PCLK16M: 16 MHz peripheral clock
PCLK32M: 32 MHz peripheral clock

RE: System Clock Frequency

Jay_Shah — Tue, 30 Jul 2019 03:44:13 GMT

Thank you for your detailed response.

So, should I infer that none of these clocks for e.g. HFINT, HFXO, and PCLK can not be pre-scaled?

RE: System Clock Frequency

bjorn-spockeli — Thu, 25 Jul 2019 08:20:15 GMT

Hi Jay,

[quote user=""]As per datasheet it states that, "The HFCLK clock controller provides the following clocks to the system." In my application I don't explicitly call HFCLKSTART task, does that mean that it always operates using HFINT or the example is internally calling this function whenever it wakes up from sleep? I've also read in couple of articles that Softdevice requires HFXO but I couldn't find any call to HFCLKSTART task.[/quote]

Yes, the CPU and most of the peripherals use the HFINT as the HFCLK source, but some peripherals like the RADIO require the HFXO to function properly.
The SoftDevice will automatically start the HFXO when it needed by the SoftDevice, so this is not something you need to handle in the application. The HFXO takes sometime to startup and stabilize so the HFINT is used util the HFXO is ready.

[quote user=""]In my sdk_config.h file, the NRF_SDH_CLOCK_LF_SRC- SoftDevice Clock source is set to NRF_CLOCK_LF_SRC_XTAL. Does that mean that the softdevice is running at 32.768KHz external crystal? If so, what exactly is running at 32.768KHz, is it the time scheduling of SoftDevice that runs with 32.768KHz or some other functionality?[/quote]

Yes, the SoftDevice uses the Low Frequency clock(LFCLK) to schedule advertisment, scan, connection events etc. The SoftDevice can either use the internal RC oscillator or an external crystal(LFXO) as the LFCLK source

The internal LFRC oscillator needs to be calibrated against the HFXO every 4 seconds to be within the +/-250ppm accuracy requirement stated in the Bluetooth specification. The LFXO will typically have an accuracy of +/-20ppm, so no calibration is needed.

Best regards

Bjørn

RE: System Clock Frequency

Dmitry — Wed, 24 Jul 2019 22:12:39 GMT

Hi,

you can find good answers here, everything is actual for nRF52 series too (except HFXO frequency that is 32 MHz instead of 16)

RE: System Clock Frequency

Jay_Shah — Wed, 24 Jul 2019 11:07:40 GMT

SDK 6.1