Inaccurate time with FreeRTOS + S112

[acanidio]

Good morning,

I'm starting to develop an application for the nRF52805 using ble_app_hrs_freertos as a base.

The modification I did are:

• Ported from nRF52832 to nRF52805
• Configured the project to use the LFRC with calibration every 8 seconds
• Changed configTICK_RATE_HZ from 1024 to 1000, that is 1kHz (sincerely I don't understand why it wasn't set to that value)
• Added a task that toggles a PIN every 1 second

I measured the time the the PIN toggles with a logic analyzer and the measured time is 1.0072539 (averaged over 20 periods) which means
an error of 0.7% and an accuracy of about 7000ppm.

From nRF52805 specification the LFRC accuracy after calibration is 500ppm. I think I am missing something. Can you possibly give me
some hint?

Best regards,

Andrea

[Vidar Berg]

Hi Andrea,

The tick rate is set to 1024 by default to avoid division error according to this post: https://devzone.nordicsemi.com/f/nordic-q-a/14157/freertos-rtc-prescaler-produces-incorrect-time. Have you tried measuring the clock accuracy with this setting as well?

Best regards,

Vidar