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.
  • The only entries are greyed-out serial ports — the board’s UART is enumerating, its debug port is not.
  • 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 udev rules (Linux) hide the probe from pyOCD. On Windows a missing driver no longer empties the list: the probe shows greyed out, with its own guide.
  • 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. Windows: check the list for a greyed-out probe

    A probe Windows has no driver for is listed, greyed out and marked [no driver], rather than missing. The "This probe has no driver" guide walks through binding it to WinUSB with Zadig, screens included.

  4. Install udev rules on Linux

    Linux needs no driver, only permission: without a rule the probe enumerates and cannot be opened. The USB permission denied guide carries a ready-made ruleset.

  5. On macOS, no driver is involved

    Debug probes are reached over HID and USB bulk, which need no kernel extension. A probe missing here is a cable, port or power problem — vendor packages for macOS install serial ports and IDE tooling, not probe access.

  6. 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.

  7. Refresh in MCUHex

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

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