About XOSC32M.CONFIG.INTCAP and XOSC32KI.INTCAP

[H-ogawa]

Hi,

I have a question about the following registers:

・XOSC32M.CONFIG.INTCAP

・XOSC32KI.INTCAP

For these, the reset value is as follows in the data sheet:

I checked these two registers with nrf54ldk, but they were not the reset values.

How is this value determined?

For example, output a specific frequency from the IC and check the actual measured value with a spectrum analyzer. If the measured value is significantly different from the expected frequency value, adjust it by changing the register setting.

Best regards,

Hiroki

[Emil Lenngren]

When you use any nRF Connect SDK project, Zephyr will set INTCAP during initialization, before main is called, according to the desired capacitance set in your board device tree file and the trim values in FICR. That is done here: https://github.com/nrfconnect/sdk-zephyr/blob/43c5dc730e385c238ce00ea91d1a772709b49abf/soc/nordic/nrf54l/soc.c#L41. For the devkits, the capacitance is set here: https://github.com/nrfconnect/sdk-zephyr/blob/43c5dc730e385c238ce00ea91d1a772709b49abf/boards/nordic/nrf54l15dk/nrf54l_05_10_15_cpuapp_common.dtsi#L31. You can use your own desired capacitance values when you create your custom board device tree file.

The LFXO INTCAP value is retained during a soft reset, while the HFXO INTCAP value is not.

[H-ogawa]

Hi Emil

Thank you for your advice.

I understood that the startup code sets the appropriate registers based on the specified load capacitance.

You have said that the HFXO INTCAP is not retained across a software reset, but is this documented anywhere?

Best regards,

Hiroki

[Emil Lenngren]

Yes, in the data sheet in the register description, all registers are by not retained unless explicitly stated otherwise.

You can see that XOSC32KI.INTCAP is marked as retained while XOSC32M.CONFIG.INTCAP is not.

I suspect this is due to the fact that the internal low frequency counter of GRTC will keep running during a soft reset or reset due to wake up from system off.