No devices found

The SDK is running but no debug probes were detected.

NO_DEVICES_FOUND

Symptoms

  • The device list is empty even though the board is plugged in.
  • pyOCD-based tools report "No available debug probes are connected".
  • The probe’s LED is on, but nothing shows up in MCUHex.

Likely causes

  • The USB cable is charge-only (no data lines) — by far the most common cause.
  • The probe is connected through a hub or dock that drops it.
  • Missing drivers (Windows) or udev rules (Linux) hide the probe from pyOCD.
  • On-board ST-Link on a Nucleo/Discovery board is in DFU/update mode or has stale firmware.

How to fix it

  1. Swap the USB cable and port

    Use a known-good data cable, plugged directly into the computer (no hub). Charge-only cables power the LED but carry no data, which looks exactly like a missing probe.

  2. Confirm the OS sees the probe

    macOS: System Information → USB. Linux: run lsusb. Windows: Device Manager. If the probe is absent at the OS level, the problem is hardware/cable, not MCUHex.

    # Linux
lsusb | grep -i -E "st|segger|cmsis"
# macOS
system_profiler SPUSBDataType | grep -i -A3 -E "st-link|j-link|cmsis"

  3. Install drivers / udev rules

    Windows: install the ST-Link driver (or J-Link package). Linux: install udev rules for your probe — see the USB permission denied guide for a ready-made ruleset.

  4. Update on-board ST-Link firmware

    Nucleo/Discovery boards with very old ST-Link firmware can enumerate oddly. Run ST’s firmware upgrade tool (STSW-LINK007) once, then replug.

  5. Refresh in MCUHex

    Click the refresh icon next to the device list after each change.

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