Creating Python OOT with gr-modtool

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This tutorial was written using GNU Radio v3.10.1.1.

Creating an OOT Module

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/

Creating an OOT Block

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

Determine whether or not you want the Python quality assurance (QA) code:

Add Python QA code? [Y/n] n

New files will be generated:

Adding file 'python/customModule/addSubSelect.py'...
Adding file 'grc/customModule_addSubSelect.block.yml'...
Editing grc/CMakeLists.txt...

Two new files were created, addSubSelect.py which defines the operation of the block and customModule_addSubSelect.block.yml which defines the interface of the block for GNU Radio Companion (GRC). The CMakeLists.txt file was modified to