MCUHex cannot talk to this device

The device is plugged in and enumerated, but it speaks over a path MCUHex has no driver for. Debugging today goes through SWD, over a CMSIS-DAP or ST-Link probe.

PROBE_TRANSPORT_UNSUPPORTED

Symptoms

  • The device appears in the list but cannot be selected.
  • Your board is plugged in over USB and its serial port shows up, yet nothing connects.
  • Only USB-to-serial adapters are listed, with no probe among them.

Likely causes

  • MCUHex reads memory over SWD, a two-wire debug port that is separate from the USB serial link. A serial connection carries whatever your firmware prints, not the chip’s memory.
  • The device is a USB-to-serial bridge (CH340, CP2102, FT232, the ACM port of a dev board), which has no access to the debug port.
  • The board is an ESP32 or another part debugged through OpenOCD, which MCUHex has no driver for yet.

How to fix it

  1. Use a debug probe

    An ST-Link, a CMSIS-DAP probe or a DAPLink adapter connects to the SWD header and is what MCUHex talks to. Many Nucleo and Discovery boards carry one on-board, exposed as a separate USB device.

  2. Wire up SWD

    Four lines are enough: SWDIO, SWCLK, GND and, on most probes, VTref so the probe matches your board’s voltage. NRST is optional and only needed for connect-under-reset.

  3. Check what is actually listed

    A probe appears with its own name — "ST-Link", "CMSIS-DAP", "DAPLink" — not as a COM or tty port. If only serial ports are listed, the probe is not enumerating; try another cable or USB port.

  4. Keep the serial port for your own output

    The serial device is not useless — it is where printf and log output go. It is simply not the path memory is read over, so both are typically connected at once.

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