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  • Case ID: 352036
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nRF54L15 RTT

garrettb

Hi

When running a project on the nRF54L15 using nRF Connect in VS Code, I often cannot connect to RTT.
I select RTT in nRF Connect, but no output appears.
If I retry multiple times (e.g., re-flashing the device, occasionally resetting, or restarting VS Code), I can eventually get RTT to connect. Once it connects successfully, it tends to work reliably for a while.
When RTT fails to connect, each attempt triggers a pop-up from SEGGER J-Link (v8.66) asking me to select the Manufacturer and Device. This adds extra delay each time.
The behavior is inconsistent: sometimes RTT works immediately, other times it requires several attempts before it stabilizes.

Could there be a setting in my project that is missing, or is this known behaviour?

Thanks

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  • 0 in reply to Priyanka
    garrettb said:

    Hi

    When running a project on the nRF54L15 using nRF Connect in VS Code, I often cannot connect to RTT.
    I select RTT in nRF Connect, but no output appears.
    If I retry multiple times (e.g., re-flashing the device, occasionally resetting, or restarting VS Code), I can eventually get RTT to connect. Once it connects successfully, it tends to work reliably for a while.
    When RTT fails to connect, each attempt triggers a pop-up from SEGGER J-Link (v8.66) asking me to select the Manufacturer and Device. This adds extra delay each time.
    The behavior is inconsistent: sometimes RTT works immediately, other times it requires several attempts before it stabilizes.

    Could there be a setting in my project that is missing, or is this known behaviour?

    Thanks

    This is common behavior with nRF54L15 + J-Link, not usually a project misconfiguration.

    Most likely causes:

    • RTT attaching before the firmware fully starts (race condition)

    • RTT control block not found because the CPU hasn’t reached main() yet

    • J-Link auto-detect instability (causes the Manufacturer/Device popup)

    What usually helps:

    • Update to the latest J-Link version + firmware

    • Enable “Connect under reset”

    • Wait a few seconds after flashing before opening RTT

    • Manually set the device to nRF54L15 instead of auto-detect

    Since it works reliably once connected, this strongly suggests a timing/attach issue rather than a missing setting.

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