nrf54l15 bluetooth stretching spi clock

[DannyDS]

Hello all,

I have an nrf54l15 on a custom board, I am having issues getting a reliable SPI clock signal when using BLE advertisements

This is the clock and correct MOSI data I am expecting to see when BLE advertisements are disabled

This is the clock signal I get when BLE advertisement is enabled

Ive stripped the program of everything other than BLE and a SPI transaction to rule anything else out.

Thanks for any suggestions.

Thanks,

Danny

[Vidar Berg]

Hello Danny,

I have not seen this before. Are you able to share a minimal version of your project so I can try to see if this issue is reproducible on a nRF54l15 DK?

Best regards,

Vidar

[DannyDS]

Hi,

here is a minimal reproducible project.

Just to note I have also discovered if you debug the application or connect to it via RTT viewer then the clock is fine. 

Thanks,

Danny

nrf54l15_spi_ble_demo.zip

[Vidar Berg]

Hi,

I don't immediately see how you are applying the pin assignments, it doesn't seem to be through pinctrl, but your zephyr user node suggests your are using the dedicated pins on port 2 with the spim21 so I suspect you may be experiencing the same as discussed in this case: https://devzone.nordicsemi.com/f/nordic-q-a/126270/nrf54l15-spi-corruption-on-gpio2-p2-when-rtt-is-disconnected/557576

Best regards,

Vidar

[DannyDS]

Hi,

Thank you for the quick reply,

Wrapping my SPI commands in  nrf_sys_event_request_global_constlat() seems to have solved the problem,

I had already come across the power modes and thought that setting nrf_power_task_trigger(NRF_POWER, NRF_POWER_TASK_CONSTLAT); 

would have been sufficient.

Many thanks,

Danny

[Vidar Berg]

Hi,

Good to hear, thanks for confirming that this was the issue.The nrf_sys_event_request_global_constlat() API is reference counted, so when it's called from the application, it prevents other modules such as the Bluetooth controller, from switching back to low-power mode until the application releases its request by calling nrf_sys_event_release_global_constlat(). The Bluetooth controller is using the constant latency sub power mode during BLE events to reduce interrupt latency.