No answer from the chip

The probe is working, but nothing answered on the SWD lines. The chip is unpowered, not wired to the probe, or its SWD pins have been switched to something else by the firmware on it.

CORTEX_M_NO_TARGET_RESPONSE

Symptoms

  • The probe appears in the device list, but connecting reports no answer from the chip.
  • The error text mentions "No device connected", "Get IDCODE error" or an unknown JTAG chain.
  • The board debugged fine until a particular firmware was flashed onto it.

Likely causes

  • The target has no power, or the probe and the board share no ground. The probe is powered by USB and will look healthy either way.
  • SWDIO and SWCLK are swapped, not connected, or broken out on a header that is not populated.
  • Firmware disabled the debug pins. On STM32F1 a single call — __HAL_AFIO_REMAP_SWJ_DISABLE() — turns PA13/PA14 into GPIO, and from the next boot the chip is silent.
  • The chip is not an SWD Cortex-M part. ESP32 and RISC-V silicon answers nothing on these lines and is indistinguishable from a broken cable from here.

How to fix it

  1. Check power and ground first

    Measure VDD on the target and confirm a ground wire runs between probe and board. A probe that enumerates over USB tells you nothing about the target rail.

  2. Verify SWDIO, SWCLK and the connector

    Compare against the board’s debug header drawing rather than memory — the 10-pin Cortex Debug connector mirrors easily on hand-crimped cables.

  3. Connect while the chip is held in reset

    If firmware takes the pins away after boot, the only window is before application code runs. STM32CubeProgrammer’s "Under reset" mode does this; so does pyOCD directly.

    pyocd commander -M under-reset

  4. If you get in, undo the pin change

    Erase the chip while you have the window, then rebuild without the SWJ-disable call — or guard it behind a delay so there is always a way back in.

    pyocd erase --mass

  5. Confirm the part is in scope

    MCUHex speaks SWD to ARM Cortex-M devices. A JTAG-only or non-ARM part produces exactly this silence no matter what is fixed on the wiring side.

Related errors