Inquiry regarding lfclk_calibration

[mmak]

Hi! 

I'm currently working on a project thats based off of the nrf desktop keyboard. I'm using the Taiyo Yuden eysgcnzxx. 

I just wanted to inquire the functionality of the lfclk calibration found in the timeout_handler function in the file m_pwr_and_clk_mgmt.c. According to the documentation, LFCLK calibration is done when the device is in Gazell mode, and the switching between xosc and rcosc is done to save power.

I was wondering how, if it applies, the above has any affect on the gazell encrypted communication with the nrf dongle? To my understanding, none of the above should affect how communication with the dongle with the exception of perhaps timeslotting? Or are they strictly used for power management?

Thanks!

[run_ar]

Hi,

lfclk calibration is performed for the RC oscillator to make sure this stays within the timing constraints of the protocol, as you mention we need to make sure we stay within the timeslot. If we did not calibrate the RC osc, it would drift over time and temperature, and eventually lead to the communication going out of sync. This is the same regardless of encryption or not.

[mmak]

Hi, thanks for the response.

Just to make sure I am interpreting what was stated correctly, the lfclk calibration is used to keep the gazelle communication in sync only if the RC oscillator is being used.

If that is the case, if I modified the code to only use the xosc high freq clock only, I would be able to ignore the calibration routine and maintain the communication sync?

Thanks.

[run_ar]

The low frequency oscillator is used for timing. But you can use the LF xtal oscillator instead of the RC oscillator if you want to avoid calibrating the RC oscillator.

[mmak]

Thanks for letting me know! 

I will move forward with removing the timers related to the lfclk calibration functions to avoid RC oscillator calibration then.