How to Build and Flash the Radio Co-Processor (RCP)

The Radio Co-Processor is a 15.4 stack image flashed onto a Silicon Labs development kit or Thunderboard Sense 2. The 15.4 stack on the development kit communicates with the higher layers of the Thread stack running on the Raspberry Pi over a USB connection.

A complete list of supported hardware for the RCP is provided on the Matter Hardware Requirements page.

First, in order to flash the RCP, connect it to your laptop directly by USB.


Step 1: Get or Build the Image File to Flash the RCP

We have provided two ways to get the required image to flash the RCP. You can use one of the following options:

  1. Use the pre-built ‘ot-rcp’ image file

  2. Build the image file from the ‘ot-efr32’ repository, which is listed on the Matter Repositories and Commit Hashes page


Using a Pre-built Image File

RCP image files for all demo boards are accessible through the Matter Artifacts Page. If you are using a pre-built image file, you can skip to Step #2: Flash the RCP.


Building the Image File from the Repository

1. Clone the ot-efr32 repository

The ‘ot-efr32’ repo is located in Github here: https://github.com/SiliconLabs/ot-efr32.

You must have Git installed on your local machine. To clone the repo use the following command:

$ git clone https://github.com/SiliconLabs/ot-efr32.git

Once you have cloned the repo, enter the repo and sync all the submodules with the following command:

$ cd ot-efr32

$ git submodule update --init

After updating the submodules you can check out the correct branch or commit hash for the system. Check the current branch and commit hash used here: Matter Branches and Commit Hashes

$ git checkout <commit hash>

2. Build the RCP

Once you have checked out the correct hash, follow the instructions here: https://github.com/SiliconLabs/ot-efr32/blob/main/src/README.md to build the RCP image for your EFR platform.

This process will build several images for your board. The filename of the image to be flashed onto the board to create an RCP is ‘ot-rcp.s37’.

The output of the build process puts all the image files in the following location: ‘/ot-efr32/build/’


Step 2: Flash the RCP

Once you get the RCP image, either by downloading a prebuilt image or building the image file from the repo, you can flash it onto your device. This is done directly from your laptop and not through the Raspberry Pi, so make sure that the device is connected directly over USB to your laptop. See How to Flash a Silicon Labs Device for more information.

Once you have flashed the image, the device becomes the RCP. Disconnect it from you laptop and connect it via USB to the Raspberry Pi.

The Raspberry Pi’s Open Thread Border Router can then use the RCP to communicate with the Thread network.