nRF54L15 GRTC SYSCOUNTER accuracy

[tmav]

Hi,

I have a general question about the GRTC accuracy on nRF54L15.

In the manual it states the following:

We will like to use the GRTC as timekeeper with an external 32.768Khz LFXO.

The system will be most of the time in sleep mode  and it will wake up from the GRTC eg. every 250ms.

During the wake up period the nRF will run from the HFINT (-10..6% accuracy).

Will this affect somehow the GRTC accuracy?

How the GRTC.SYSCOUNTER manages to synchronize the 32.768Khz LFXO (high accuracy) with the 16Mhz clock (low accuracy) and have 1us resolution?

What about the GRTC accuracy during the wake up period?

Best Regards

[Kazi Afroza Sultana]

Hello,

From the documentation ''Automatic synchronization of SYSCOUNTER with the internal low frequency timer for ultra-low power operation

• Internal low frequency timer runs on LFCLK (32768 Hz clock)
• Internal low frequency timer can run while the device is in System OFF mode''

The SYSCOUNTER runs off the fast clock (16MHz clock) but uses only LFCLK while SYSCOUNTER is in sleep state.

GRTC's timekeeping accuracy is determined by LFXO, not by the HFINT. The 16MHz HFINT is used for high resolution counting during active periods, it doesn't have any long-term effect because LFXO can resynchronize periodically.

So, I think you can use GRTC as timekeeper with an external LFXO as long as the quality of LFXO is good.

However, I have asked the team to make it assure. I will get back to you soon.

Thanks.

BR
Kazi 

[tmav]

Hello Kazi.

Many thanks for your answer.