srx‐programmer
The description below primarily focuses on Windows systems. For Linux and Mac, the steps will be slightly different.
The Arduino Due has two USB ports. The srx-programmer firmware uses the so called "native usb" port. This is the USB port right next to the reset button of the Arduino due. You can only use this port for using the software.
To update the srx-programmer firmware, you install the Arduino IDE 2. You can get this from from here. Download and install the latest version of it.
When the Arduino Due is first connected to the computer, it should be automatically detected by the operating system. A driver installation should not be necessary. However, the Arduino IDE will install a bunch of drivers in the next step anyway.
These popups will probably also display already what (serial) COM ports the device has been assigned to. Take note of this COM port if it is shown. If this isn't displayed, it's not a problem.
Launch the Arduino 2 IDE. The first thing you'll notice is the the Arduino IDE loads content from the Internet and that it wants to install a driver. This is all normal and you should confirm everything (click "install").
You'll notice when the downloads are done, when the output window doesn't do anything anymore.
Now, you'll need to select the Arduino Due as the development board. For that, click "Select Board" in the main toolbar.
Search for "Due" in the "Search board" field. This will be greyed out which means that the board packages haven't been installed yet for the Arduino IDE. Just click the entry "Arduino Due", don't worry about the ports and confirm with "ok".
Once you have done that, the Arduino IDE will promp you to install the "Arduiono SAm Board" core. Click "Yes".
Once you have done that, the Arduino IDE will once again download and install packages.
When it is done, the Arduino IDE will prompt you to reselect the board. Click "Yes".
The board selector now reopens with slightly different settings. You can now choose between "Arduino Due (Native USB Port)" and "Arduino Due (Programming Port)". Select the "Arduino Due (Native USB Port)" with the corresponding COM port shown when it was first detected. Click "OK".
The Arduino IDE is now ready to program the firmware.
Grab the srx-programmer.ino file from the github repository. Either download it or clone the git repository if you know how to do that.
Open this file in the Arduino IDE.
The Arduino IDE will prompt you that it wants to move the sketch. You can confirm this with "OK".
A new window opens with the programmer firmware. If you like, you can inspect the code to make sure it won't harm you. Once ready, you can start the programming by clicking the right-arrow button:
The sketch will then compile and upload.
If everything went smoothly, you are done with loading the firmware.