Download the ‘culfw’ current version from :
Current version I found is 1.66.
Go to ‘culfw-1.66/Devices/CUL/’ directory and run the following command in the terminal.
sudo make usbprogram_v3
The cul device now should start blinking.
Test your device by running an application.
Install the package dfu-programmer,
sudo apt-get install dfu-programmer
sudo apt-get install build-essential
then execute “make usbprogram”
After flashing the CUL, a new USB device should appear: “03eb:204b Atmel Corp.”. If not reinsert the device without pressing the micro-switch.
There are other options which you can find in this link:
It’s in German, but with translation works fine for this.