UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Einar Thorsrud — Mon, 14 Apr 2025 12:50:42 GMT

Hi,

On the nRF54L15, the Bluetooth stack (specifically MPSL) will disable constant latency mode unless it is enabled in a way it knows about. Therefor, CONFIG_SOC_NRF_FORCE_CONSTLAT=y will not work in this case.

To use constant latency with Bluetooth, you can add CONFIG_NRFX_POWER=y to prj.conf and enable constant latency using nrfx_power_constlat_mode_request().

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Agustin Perez — Fri, 11 Apr 2025 13:50:28 GMT

Hi,

Thank you for your prompt follow-up and for reproducing the issue on your end.

As we are approaching production soon, I would greatly appreciate it if you could keep me informed of any updates or findings related to this issue. If a workaround becomes available, please do let me know.

Thank you again for your support.

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Håkon Alseth — Fri, 11 Apr 2025 13:38:38 GMT

Hi,

Thank you for your patience in this matter and confirming that CONSTLAT is indeed set. I have been able to reproduce this with the smp_svr sample, by enabling UARTE21, and see that the uart output is corrupted just as you mention.

I have reported this internally and alerted the team(s) in question.

Kind regards,

Håkon

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Agustin Perez — Thu, 10 Apr 2025 13:50:20 GMT

Hi,

I’ve added the following line:

// Set register
NRF_POWER->TASKS_CONSTLAT = 1;

However, the issue still persists. The UART works correctly when BLE is not enabled, but once advertising starts, the UART stops working or freezes.

Do you have any idea what might be causing this behavior?

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Håkon Alseth — Thu, 10 Apr 2025 09:06:16 GMT

Hi,

Thank you so much for providing a detailed and proper overview of the issue that you are seeing.

[quote user="Agustin Perez"]I'm using P2.07 and P2.08 for UARTE21 [/quote]

When crossing domains, ie. using P2 pins on UARTE2x (and TWIM2x/SPIM2x), there is a requirement to enable constant latency mode:

RE: nRF54L15: UART pinout not working unless connecting the RTT viewer

This is unfortunately not documented yet from our side, but will be in the future. My deepest apologies for the inconvenience this is causing you. I will also convey internally that this will need driver transport logic added.

Kind regards,

Håkon

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Agustin Perez — Wed, 09 Apr 2025 18:20:30 GMT

I'm not using the DK, I have a custom board.

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

khelmutlord — Wed, 09 Apr 2025 18:18:24 GMT

If you are using the nRF54L15-DK, please use the board configurator to disable the debugger once your application is running. P2.07 is connected to the onboard debugger as it also serves as SWO. This may be the issue.

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Agustin Perez — Wed, 09 Apr 2025 14:38:47 GMT

I'm using P2.07 and P2.08 for UARTE21 and P2.02, P2.04, P2.05 and P2.06 for SPI00.

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

Agustin Perez — Wed, 09 Apr 2025 14:37:34 GMT

[deleted]

RE: UARTE21 and SMP Bluetooth conflict on nRF54L15 – works only with debugger attached

khelmutlord — Wed, 09 Apr 2025 14:32:35 GMT

Could you share the pins you are using for SPI00 and UARTE21?