Blinky LED fails to run on nRF5340 DK dev kit

RE: Blinky LED fails to run on nRF5340 DK dev kit

Einar Thorsrud — Thu, 31 Jul 2025 07:36:44 GMT

Hi,

Is it so that you built for nrf5340_audio_dk/nrf5340/cpuapp/ns but are testing on a nRF5340 DK? If so, this will not work as these are different boards which does not have LEDs on the same pins. Wiht the nRF52840 DK, you should build for nrf5340dk/nrf5340/cpuapp (or nrf5340dk/nrf5340/cpuapp/ns but I would avoid that for not for simplicity and to reduce build time as you probably do no need TF-M at this stage).

RE: Blinky LED fails to run on nRF5340 DK dev kit

astorm — Wed, 30 Jul 2025 13:47:31 GMT

Hi Einar, I will avoid testing any of the Zephyr sample code for the moment.

As a sanity check I tried to repeat the blinky example described at

Exercise 2 - Build and flash your first nRF Connect SDK application - Nordic Developer Academy

and after creating a new application based on the nrf samples, I made a new build configuration following the instructions, targeted a "nrf5340_audio_dk/nrf5340/cpuapp/ns" and the build reported success after several minutes:

I then tried flashing this back into the nRF5340 which also reported success

The big problem is this time I dont see any LEDs actually flashing on the PCB. 😕

Given I repeated the DevZone example this is worrying, so I thought maybe build a debug optimised version of this sample and step through the code with breakpoints to check the code is running on the target cpu. The build stage reports success and flashing also reported success:

Attaching the debugger to the target appears to be ok but still no evidence of LEDs flashing 😕

It appears the code is doing nothing more than constantly calling k_cpu_idle() from the source file "c:\ncs\v3.0.2\zephyr\kernel\idle.c" with no evidence of any code that turns the LED on or off which explains why I dont see this.

Something is clearly fundamentally very wrong

RE: Blinky LED fails to run on nRF5340 DK dev kit

Einar Thorsrud — Wed, 30 Jul 2025 07:10:53 GMT

Hi,

The samples under nrf are officially supported in the SDK. The sampls under zephyr come from vanilla Zephyr and often works, but are not officially supported in the nRF Connect SDK (they will often be usefull, but may not always work as they are not officially supported or tested during SDK releases). See Samples.

RE: Blinky LED fails to run on nRF5340 DK dev kit

astorm — Tue, 29 Jul 2025 16:03:01 GMT

Update: I have tried to recreate this issue and noticed there are two blinky examples on my HDD and the second demonstrates the failure above but the first does not and will flash a a real LED on the target Dev Kit.

Superficially this is problem solved, but it was a 50/50 chance I pick the working sample.

I did successfully build and run the third sample seen above which uses a PWM pattern to flash the LED.