User:Muaddib

Understanding XMLRPC Blocks

This tutorial presents the GNU Radio XMLRPC blocks. There are two blocks in this collection: XMLRPC Client and XMLRPC Server. Both blocks have IP address/port fields while the Client block also has callback and variable fields. The blocks use the Python XMLRPC module and use a subset of the full XMLRPC spec.

XMLRPC is an XML-based Remote Protocol Control mechanism that does just that. It uses HTTP transport and allows a client to use SET commands to change parameters on a server or use GET commands to obtain the value of parameters on the server.

To understand better how GNURadio implements XMLRPC, look at the block documentation linked in the paragraph above.

To understand the XMLRPC protocol and Python implementation in detail, the reference links below are a good starting point.

Reference Links

http://xmlrpc.com

https://docs.python.org/3.8/library/xmlrpc.html

Prerequisites

• Intro to GR usage: GRC and flowgraphs
• Simulation Example: Narrowband FM Transceiver
• Understanding ZMQ Blocks

Introduction: What does XMLRPC do in GNURadio and Why Should I Care?

WHAT: In GNURadio placing the XMLRPC Server block in a flowgraph will create an XMLRPC server that exposes all the variables in the flowgraph and allows a client to control them at runtime. The XMLRPC Client block allows the user to control all the parameters of another flowgraph that contains the XMLRPC Server block.

WHY: In many cases, we have need to adjust the variables of a flowgraph at runtime. We usually do this with a QT GUI block in the flowgraph we want to control. But what if you want to have the same control interface in a different flowgraph? XMLRPC will allow you to control all of a flowgraph's variables from a second flowgraph using HTTP. In fact, the second flowgraph doesn't even have to be on the same computer!

Building on Knowledge

• First we will start with running the basic client/server example flowgraphs from the GNU Radio source tree (gr-blocks/examples/xmlrpc).

• Next, we will add XMLRPC control to flowgraphs from the Narrow Band FM GNURadio tutorial to add remote control capability.

• Finally, we will combine ZMQ sockets to stream data into to our control flowgraph so we can display streaming data, allowing us to see the effect of the control messages we send.

• (OPTIONAL) As a bonus step we will run the server/client pair using 2 computers.

Simple Example

<run the source examples>

Add Control Functionality to the NB FM Example

• Run on localhost
• Run on separate machines

  *<ssh -L vs. direct IP>
  *notes about streaming IQ vs Decimated I/Q
  *show data usage of I/Q vs. decimated I/Q

Expand the Remote Controller with Streaming Data

• audio output to ZMQ