Image corruption only when RTT is not connected (nRF54L15 / NCS)

[Moh]

Hi Nordic team,

I’m seeing a strange runtime behavior related to RTT connection state.

Issue summary

• When I connect to RTT (Segger/J-Link RTT viewer), image rendering on the display is stable and I do not see corruption.
• When RTT is not connected, the same firmware shows visible image corruption on the display.

Platform / setup

• MCU: nRF54L15 (CPUAPP)
• SDK: nRF Connect SDK (Zephyr-based)
• Logging backend: RTT enabled in my debug setup
• Display content includes image updates (RGB565 image pipeline)
• ncs sdk version: 3.1.0

Observed behavior

• With RTT attached: image output looks correct
• Without RTT attached: intermittent/clear corruption appears in displayed images
• No functional code changes between both cases; only RTT attachment state changes

What I suspect

• A timing-sensitive issue/race condition (RTT connection likely changes timing enough to hide the bug)
• Possibly related to interrupt locking/unlocking, display update synchronization, DMA/SPI transfer timing, or buffer ownership/lifetime

Kindly please provide some support on this. I am attaching prj.conf and dts file 

Thanks

Moh

4278.boards.zip0068.prj.conf

[Ingfu]

Hi,

I can't really help, but we do have a similar issue using a Timer, Counter, GPIOTE, SPI - PPI setup. When constlat is enabled, no issues. When constlat is not enabled and the timer has no interrupt enabled, we miss events. If we enable the interrupt for the timer and have an empty ISR, no issues even running for several days.