Typically, the firmware of the {IDF_TARGET_NAME} is flashed via the chip's serial port. However, flashing via the serial port requires a USB to serial converter chip (e.g., CP210x or FTDI) to be connected to the {IDF_TARGET_NAME} (see :doc:`Establish Serial Connection with {IDF_TARGET_NAME} <../get-started/establish-serial-connection>` for more details). The {IDF_TARGET_NAME} contains a USB OTG peripheral making it possible to connect the {IDF_TARGET_NAME} to the host directly via USB (thus not requiring a USB to serial converter chip).
Device Firmware Upgrade (DFU) is a mechanism for upgrading the firmware of the {IDF_TARGET_NAME} directly via the Universal Serial Bus (USB). However, enabling Secure Boot or flash encryption disables the USB-OTG USB stack in the ROM, disallowing updates via the serial emulation or DFU on that port.
Some cables are wired up with non-standard colors and some drivers are able to work with swapped D+ and D- connections. Please try to swap the cables connecting to D+ and D- if your device is not detected.
By default, the :doc:`USB_SERIAL_JTAG <usb-serial-jtag-console>` module is connected to the {IDF_TARGET_NAME}'s internal USB PHY, while the USB OTG peripheral can be used only if an external USB PHY is connected. Since DFU is provided via the USB OTG peripheral, it cannot be used through the internal PHY in this configuration.
However, users can permanently switch the internal USB PHY to work with USB OTG peripheral instead of USB_SERIAL_JTAG by burning the ``USB_PHY_SEL`` eFuse. See *{IDF_TARGET_NAME} Technical Reference Manual* [`PDF <{IDF_TARGET_TRM_EN_URL}>`__] for more details about USB_SERIAL_JTAG and USB OTG.
..note::
The {IDF_TARGET_NAME} chip needs to be in bootloader mode before it can be detected as a DFU device and flash. This can be achieved by pulling GPIO0 down (e.g., pressing the BOOT button), pulling RESET down for a moment, and releasing GPIO0.
Do not forget to set the target chip by ``idf.py set-target`` before running ``idf.py dfu``. Otherwise, you might create an image for a different chip or receive an error message like ``unknown target 'dfu'``.
The command relies on `dfu-util <http://dfu-util.sourceforge.net/>`_. Please see :ref:`get-started-get-prerequisites` for installing ``dfu-util``. ``dfu-util`` needs additional setup for :ref:`api_guide_dfu_flash_win` or setting up an :ref:`api_guide_dfu_flash_udev`. macOS users should be able to use ``dfu-util`` without further setup.
Consequently, the desired device can be selected for flashing by the ``--path`` argument. For example, the devices listed above can be flashed individually by the following commands::
The vendor and product identificators are set based on the selected chip target by the ``idf.py set-target`` command and they are not selectable during the ``idf.py dfu-flash`` call.
Udev is a device manager for the Linux kernel. It allows us to run ``dfu-util`` (and ``idf.py dfu-flash``) without ``sudo`` for gaining access to the chip.
Please check the output of the command ``groups``. The user has to be a member of the `GROUP` specified above. You may use some other existing groups for this purpose (e.g., `uucp` on some systems instead of `plugdev`) or create a new group for this purpose.
Please see the `libusb wiki <https://github.com/libusb/libusb/wiki/Windows#How_to_use_libusb_on_Windows>`_ for more details.
The drivers can be installed by the `Zadig tool <https://zadig.akeo.ie/>`_. Please make sure that the device is in download mode before you run the tool and that it detects the {IDF_TARGET_NAME} device before you install the drivers. The Zadig tool might detect several USB interfaces of {IDF_TARGET_NAME}. Please install the WinUSB driver only for the interface where there is no driver installed (probably it is Interface 2) and do not re-install the driver for the other interface.
-``dfu-util: command not found`` might indicate that the tool has not been installed or is not available from the terminal. An easy way of checking the tool is running ``dfu-util --version``. Please see :ref:`get-started-get-prerequisites` for installing ``dfu-util``.
- The reason for ``No DFU capable USB device available`` could be that the USB driver was not properly installed on Windows (see :ref:`api_guide_dfu_flash_win`), udev rule was not setup on Linux (see :ref:`api_guide_dfu_flash_udev`) or the device is not in bootloader mode.
- Flashing with ``dfu-util`` on Windows fails on the first attempt with error ``Lost device after RESET?``. Please retry the flashing and it should succeed the next time.
When Secure Download Mode is enabled, DFU is no longer possible. Please see :doc:`Flash Encryption <../security/flash-encryption>` guide for more details.
