Micro XRCE-DDS Agents receive messages containing Operations from Clients. Agents keep track of the Clients and the Micro XRCE-DDS Entities they create. The Agent uses the Entities to interact with DDS Global Data Space on behalf of the Client.

The communication between a Micro XRCE-DDS Client and a Micro XRCE-DDS Agent supports three kind transport: UDP, TCP, or SerialPort. While running Micro XRCE-DDS Agent will attend any received request from your Micro XRCE-DDS Clients. Micro XRCE-DDS Agent answers back with the result of a request each time a request is attended.

The Agent supports being run by the user like this:

 $ micro-xrce-dds-agent --help

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

 $ snap set micro-xrce-dds-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-xrce-dds-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-xrce-dds-agent transport="new transport"
  
  

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

   $ snap set micro-xrce-dds-agent middleware="new middleware"
  
  

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

   $ snap set micro-xrce-dds-agent verbosity="selected verbosity"
  
  

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

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

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

   $ snap set micro-xrce-dds-agent discovery-port="selected port"
  
  

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

   $ snap set micro-xrce-dds-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-xrce-dds-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-xrce-dds-agent baudrate="baud rate"
  
  

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

   $ snap set micro-xrce-dds-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-xrce-dds-agent
       slots:
       - snapd:cp2102cp2109uartbrid (allows accessing a specific serial port)
    
    

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

     $ snap connect micro-xrce-dds-agent:serial-port snapd:cp2102cp2109uartbrid
    
    

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