Creating Python OOT with gr-modtool

Beginner Tutorials Introducing GNU Radio What is GNU Radio? Installing GNU Radio Your First Flowgraph Flowgraph Fundamentals Python Variables in GRC Variables in Flowgraphs Runtime Updating Variables Signal Data Types Converting Data Types Packing Bits Streams and Vectors Hier Blocks and Parameters Creating and Modifying Python Blocks Creating Your First Block Python Block With Vectors Python Block Message Passing Python Block Tags DSP Blocks Low Pass Filter Example Designing Filter Taps Sample Rate Change Frequency Shifting Reading and Writing Binary Files SDR Hardware RTL-SDR FM Receiver B200-B205mini FM Receiver

TODO: fill out some introductory info TODO: add this tutorial to the nav bar

This tutorial was written using GNU Radio v3.10.1.1.

Open a terminal and navigate to an appropriate directory for writing software, such as the home directory:

$ cd $HOME

GNU Radio comes packaged with gr_modtool, software used to create out-of-tree (OOT) modules. An OOT module can be thought of as a collection of custom GNU Radio blocks. Create an OOT module named customModule using gr_modtool:

$ gr_modtool newmod customModule

The directory gr-customModule is created which contains all of the skeleton code for an OOT module, however it does not yet have any blocks. Move into the gr-customModule directory:

$ cd gr-customModule

List all of the files and directories within the OOT module:

$ ls

The directory listing will be as follows:

apps/  cmake/  CMakeLists.txt  docs/  examples/  grc/  include/  lib/  MANIFEST.md  python/

Now a block needs to be created within gr-customModule. The custom block will either add or subtract based on an input parameter, so the block is named addSubSelect:

$ gr_modtool add addSubSelect

The command will start a questionnaire about how to the block is to be defined: what block type, language and parameters:

GNU Radio module name identified: customModule
('sink', 'source', 'sync', 'decimator', 'interpolator', 'general', 'tagged_stream', 'hier', 'noblock')

Select the sync block, which produces an output for every input:

Enter block type: sync

Enter python as the language:

Language (python/cpp): python
Language: Python
Block/code identifier: addSubSelect

Enter the name or organization of the copyright holder:

Please specify the copyright holder: YourName

Now enter the argument list:

Enter valid argument list, including default arguments:

Enter the argument list as if writing the Python code directly. In this case the selector will determine whether or not the block performs addition or subtraction. A default argument of True is given:

selector=True