Using a different frequency LFXO with nRF53

RE: Using a different frequency LFXO with nRF53

JONATHAN LL — Wed, 02 Feb 2022 10:01:08 GMT

Thanks for the explanation, but no you would not be able to successfully use anything other then 32.768 kHz crystal.

Regards,
Jonathan

RE: Using a different frequency LFXO with nRF53

Stephan Walter — Tue, 01 Feb 2022 15:41:28 GMT

Hi Jonathan,

as I said we would like to have the frequency divisible by 1200Hz, 1600Hz and 2400Hz.

We are trying to sample a datastream which can have one of these baud rates (using oversampling with an integer factor). With a 32768 Hz LFXO, we would need to use a RTC compare interrupt and reload the compare register with values just above or below the target interval, which would not be an integer.

This would require waking the core for each sample and would also introduce jitter to the sample time. Using an LFXO with a multiple of the listed frequencies would allow us to avoid these disadvantages.

Best regards,

--Stephan Walter

RE: Using a different frequency LFXO with nRF53

JONATHAN LL — Tue, 01 Feb 2022 14:15:09 GMT

Hi,

The nrf5349 needs to have the LFXO stay within the spec, https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/oscillators/doc/oscillators.html?cp=3_0_0_3_11_4_1#unique_63981518 , so no you cant change the Hz.

[quote user=""]32768 Hz is not very convenient for us.[/quote]

Why is this?

Regards,
Jonathan

RE: Using a different frequency LFXO with nRF53

Stephan Walter — Tue, 01 Feb 2022 07:02:46 GMT

Hi sipan112, I don't see how any of this is relevant to my question.

RE: Using a different frequency LFXO with nRF53

sipan112 — Mon, 31 Jan 2022 20:24:42 GMT

The application core clocks can be scaled from their respective HFCLK clocks.

The application core clock HCLK128M can at any time be scaled from the HFCLK128M clock using the HFCLKCTRL register.

The HCLK192M clock can be scaled from the HFCLK192M clock using the HFCLK192MCTRL register.

Note: Settings Div1 and Div2 in HFCLK192MCTRL register will result in increased power consumption.

The ACLK audio clock cannot be scaled from the HFCLKAUDIO clock. Instead, its frequency can be configured in the relevant peripherals. Refer to the Audio oscillator for more information on the audio clock and related peripherals.

Note: It is possible to scale the application core clocks at any time, for instance when a clock has already has been started, without having to stop it first.