Device Firmware Upgrade via USB

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Typically, the firmware of the ESP32-S2 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 ESP32-S2 (see Establish Serial Connection with ESP32-S2 for more details). The ESP32-S2 contains a USB OTG peripheral making it possible to connect the ESP32-S2 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 ESP32-S2 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.

USB Connection

The necessary connections for the ESP32-S2's internal USB PHY (transceiver) are shown in the following table:

GPIO

USB

20

D+ (green)

19

D- (white)

GND

GND (black)

+5V

+5V (red)

Warning

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.

Note

The ESP32-S2 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.

Building the DFU Image

The command below will create a DFU image named dfu.bin that is placed in the project's build directory:

idf.py dfu

Note

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'.

Flashing the DFU Image

The command below will download the DFU image into the ESP32-S2:

idf.py dfu-flash

The command relies on dfu-util. Please see Software for installing dfu-util. dfu-util needs additional setup for USB Drivers (Windows Only) or setting up an Udev Rule (Linux Only). macOS users should be able to use dfu-util without further setup.

If there are more boards with the same chip connected then idf.py dfu-list can be used to list the available devices, for example:

Found Runtime: [303a:0002] ver=0723, devnum=4, cfg=1, intf=2, path="1-10", alt=0, name="UNKNOWN", serial="0"
Found Runtime: [303a:0002] ver=0723, devnum=6, cfg=1, intf=2, path="1-2", alt=0, name="UNKNOWN", serial="0"

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:

idf.py dfu-flash --path 1-10
idf.py dfu-flash --path 1-2

Note

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.

See Common Errors and Known Issues and their solutions.

Udev Rule (Linux Only)

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.

Create file /etc/udev/rules.d/40-dfuse.rules with the following content:

SUBSYSTEMS=="usb", ATTRS{idVendor}=="303a", ATTRS{idProduct}=="00??", GROUP="plugdev", MODE="0666"

Note

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.

Restart your computer so the previous setting could take into affect or run sudo udevadm trigger to force manually udev to trigger your new rule.

USB Drivers (Windows Only)

dfu-util uses libusb to access the device. You have to register on Windows the device with the WinUSB driver.

Please see the libusb wiki for more details.

The drivers can be installed by the Zadig tool. Please make sure that the device is in download mode before you run the tool and that it detects the ESP32-S2 device before you install the drivers. The Zadig tool might detect several USB interfaces of ESP32-S2. 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.

Warning

The manual installation of the driver in Device Manager of Windows is not recommended because the flashing might not work properly.

Common Errors and Known Issues

  • 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 Software 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 USB Drivers (Windows Only)), udev rule was not setup on Linux (see Udev Rule (Linux Only)) 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.

Secure Download Mode

When Secure Download Mode is enabled, DFU is no longer possible. Please see Flash Encryption guide for more details.

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