Micro-ROS, whose default implementation is based on eProsima's Micro XRCE-DDS middleware, is composed of client applications which interact with the ROS 2 world by means of an Agent. This agent keeps tracks of the entities created by means of requests performed on the microcontroller side, and uses them to communicate with the ROS 2 dataspace.

Being an extension of the Micro XRCE-DDS Agent, the micro-ROS agent supports being run by the user like this:

   $ micro-ros-agent --help

In addition, the Agent supports running as a service that can be enabled with:

   $ snap set micro-ros-agent daemon=true

If the service is enabled, by default it uses the udp4 transport on port 8888. The following parameters can be changed (these are specific to the service, the micro-ros-agent command simply takes command-line arguments, but the capabilities are the same):

• transport. Supported transports are udp4, udp6, tcp4, tcp6, serial, and pseudoterminal. Default is udp4. Change with:

   $ snap set micro-ros-agent transport="new transport"
  
  

• middleware. Supported kinds of middleware are ced, rtps, and dds. Default is dds. Change with:

   $ snap set micro-ros-agent middleware="new middleware"
  
  

• verbosity. Supported verbosity levels are 0-6, defaulting to 4. Change with:

   $ snap set micro-ros-agent verbosity="selected verbosity"
  
  

• discovery. Enable or disable the discovery server. Defaults to "false". Change with:

   $ snap set micro-ros-agent discovery="true or false"
  
  

• discovery-port. Port on which the discovery server (see above) listens. Defaults to 7400. Change with:

   $ snap set micro-ros-agent discovery-port="selected port"
  
  

• p2p-port. Port to use for the P2P profile. Change with:

   $ snap set micro-ros-agent p2p-port="selected port"
  
  

• port. Port on which the agent listens. Only applicable to one of the UDP or TCP transports (see above). Defaults to 8888. Change with:

   $ snap set micro-ros-agent port="selected port"
  
  

• baudrate. Baud rate to use when accessing serial ports. Only applicable when using the serial or pseudoterminal transport. Defaults to 115200. Change with:

   $ snap set micro-ros-agent baudrate="baud rate"
  
  

• device. The serial device to use. Only applicable when using the serial or pseudoterminal transport. Change with:

   $ snap set micro-ros-agent device="device path"
  
  

When using the snap with a serial device, some steps need to be taken in order to establish a successful connection:

• Refresh your local installation of the snap core package:

   $ sudo snap refresh core --edge
  
  

• Enable the hotplug feature and restart the snapd daemon:

   $ sudo snap set core experimental.hotplug=true
   $ sudo systemctl restart snapd
  
  

• After plugging the microcontroller to the serial port, execute the snap interface serial-port command. You should see something like this:

     name:    serial-port
     summary: allows accessing a specific serial port
     plugs:
       - micro-ros-agent
     slots:
     - snapd:cp2102cp2109uartbrid (allows accessing a specific serial port)
  
  

• Connect your snap image to the desired serial port (replace accordingly):

   $ snap connect micro-ros-agent:serial-port snapd:cp2102cp2109uartbrid
  
  

After this, you can execute your snap as usual, using micro-ros-agent serial -d <serial-dev>.