Connection lost

The connection to the SDK server was dropped.

SDK_CONNECTION_LOST

Symptoms

  • A working session suddenly reports "Connection lost".
  • Live monitor values freeze, then the UI shows the SDK as unreachable.
  • The SDK terminal shows a crash trace or simply closed.

Likely causes

  • The SDK process crashed or was terminated (closed terminal, system sleep, OS update).
  • The computer went to sleep and dropped local sockets.
  • A USB error inside the SDK (probe yanked mid-transfer) took the process down.

How to fix it

  1. Check the SDK process

    Look at the terminal or tray where the SDK runs. If it crashed, the last lines of output usually name the cause (USB error, Python exception).

  2. Restart the SDK

    Start the SDK again, then click retry in MCUHex. Your project, symbols and monitor layout are preserved in the browser — only the live link needs to be rebuilt.

  3. Prevent sleep during long sessions

    If this happens during long monitoring runs, disable system sleep (or use caffeinate on macOS) so the OS does not tear down the local socket.

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