# Device Firmware Upgrade through USB¶

Device Firmware Upgrade (DFU) is a mechanism for upgrading the firmware of devices through Universal Serial Bus (USB). DFU is supported by ESP32-S2 chips. The necessary connections for the USB peripheral are shown in the following table.

GPIO

USB

20

D+ (green)

19

D- (white)

GND

GND (black)

+5V

+5V (red)

Note

The ESP32-S2 chip needs to be in bootloader mode for the detection as a DFU device and flashing. This can be achieved by pulling GPIO0 down (e.g. pressing the BOOT button), pulsing RESET down for a moment and releasing GPIO0.

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.

The software requirements of DFU are included in Step 1. Install prerequisites of the Getting Started Guide.

Section Building the DFU Image describes how to build firmware for DFU with ESP-IDF and Section Flashing the Chip with the DFU Image deals with flashing the firmware.

## Building the DFU Image¶

The DFU image can be created by running:

idf.py dfu


which creates dfu.bin in the build directory.

Note

Don’t 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 something like unknown target 'dfu'.

## Flashing the Chip with the DFU Image¶

idf.py dfu-flash


which relies on dfu-util. Please see Step 1. Install prerequisites for installing dfu-util. dfu-util needs additional setup for USB drivers (Windows only) or setting up an udev rule (Linux only). Mac OS 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 it is 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 command groups. The user has to be a member of the GROUP specified above. You may use some other existing group 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 running the tool and that it detects the ESP32-S2 device before installing the drivers. The Zadig tool might detect several USB interfaces of ESP32-S2. Please install the WinUSB driver for only that interface for which there is no driver installed (probably it is Interface 2) and don’t 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 hasn’t been installed or is not available from the terminal. An easy way of checking the tool is running dfu-util --version. Please see Step 1. Install prerequisites for installing dfu-util.

• The reason for No DFU capable USB device available could be that the USB driver wasn’t properly installed on Windows (see USB drivers (Windows only)), udev rule was not setup on Linux (see udev rule (Linux only)) or the device isn’t 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.