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This article explains the current architecture of gr_modtool in the python3 branch.

What is gr_modtool?

While developing an Out Of Tree module, there's a lot of boring, monotonous work involved: boilerplate code, makefile editing, etc. gr_modtool is a script which aims to help with all these things by automatically editing makefiles, using templates, and doing as much work as possible for the developer such that you can jump straight into the DSP coding.

Note that gr_modtool makes a lot of assumptions on what the code looks like. The more your module is custom and has specific changes, the less useful gr_modtool will be, but it is probably the best place to start with any new module or block. You can go through the block coding guide for getting an insight of coding the block.

gr_modtool is available in the GNU Radio source tree and is installed by default.

Plug-in Architecture

gr-modtool uses the Click Python package for its command line interface. Some of the advantages of using Click for CLI are:-

  • Click is fully nestable and composable.
  • Click supports for prompting of custom values.
  • Click works the same in Python 2 and 3.
  • Click comes with useful common helpers like ANSI colors.
  • Click is very simple to code and visualize.

Click is based on decorators and therefore enables simple syntax for calling high order internal functions.

gr_modtool uses the class click.Group as the parent class for its base module's CommandCLI class. The parent class functions list_commands and get_command have been overridden in the child class to enable a plug-in architecture for gr_modtool.

The function list_commands lists all the commands for the gr_modtool. It first searches for the in-tree commands, the commands in its own directory, and then searches for other registered commands through external plug-ins or otherwise (in case of the modtool, they are only registered through external plug-ins).
The function get_command returns a command object by the user input command. It first tries to import the module for the command by searching the in-tree modules, then checks for the registration of command via other sources. If the module is found in-tree, then the cli() function of the respective module is called.

Request-Response cycle

Initially all requests with gr_modtool in the command-line interface by the user passes through the cli() function of If no further command is provided in the command-line, the help page is displayed with all the in-tree plug-ins commands as well as commands from the external plug-ins, if any.

If a command (after gr_modtool) is provided in the interface which has a corresponding module (where the command is the user input command) the cli() function of the corresponding module is invoked with the context of the group instance in the base module.

The function is decorated by the decorator @click.command() which add the functionalities of the class click.Command and automatically attach the decorated options and arguments to it. The user input values of all these parameters are then passed to the run() function of the respective module defined in its core class.

Note: The basic difference between arguments and options is that arguments are mandatory (by default, can be made optional as in the case with the modtool scripts) and positional. Moreover, documentation of the argument is not generated by click and it has to be done manually.

Key Notes

  • A decorator function common_params is present in the base module to remove the redundancy of adding the same options in every module. These options haven't been provided as the options to the base command group intentionally because they actually make sense with the command itself and otherwise the command gr_modtool add -t general --skip-lib will look like gr_modtool add --skip-lib -t general which won't be user-friendly. Therefore, these parameters will show up in the help page of the respective command rather than the command group.
  • A decorator block_name is present in the base module which adds an argument (non-mandatory) block_name to the particular command which uses it.
  • The help page for a particular command can be shown with --help in the CLI. For eg:- gr_modtool add --help.
  • For commands, a short help snippet is generated. By default, it’s the first sentence of the help message of the command, unless it’s too long. This can also be overridden by short_help provided with command. For example, @click.command('newmod', short_help=ModToolNewModule().description) shows the help of the command newmod generated in the help page (gr_modtool --help or simply gr_modtool) as the description variable of the class ModToolNewModule. The main help-text when you run the command's help page, eg:- gr_modtool makexml --help is the document string of the function attached to the decorator @click.command.
  • For options, the help documentation can be added by help parameter in the decorator @click.option(). For example, @click.option('--copyright', help="Name of the copyright holder (you or your company) MUST be a quoted string.").

The help page of gr_modtool looks like:-

% gr_modtool
Usage: gr_modtool [OPTIONS] COMMAND [ARGS]...

  A tool for editing GNU Radio out-of-tree modules.

  --help  Show this message and exit.

  add      Adds a block to the out-of-tree module.
  disable  Disable selected block in module.
  info     Return information about a given module
  makexml  Generate XML files for GRC block bindings.
  newmod   Create new empty module, use add to add blocks.
  rename   Rename a block inside a module.
  rm       Remove a block from a module.

  Manipulate with GNU Radio modules source code tree. Call it without
  options to run specified command interactively

The help page of the command add of gr_modtool looks like:-

 % gr_modtool add --help
Usage: gr_modtool add [OPTIONS] BLOCK_NAME

  Adds a block to the out-of-tree module.

  -t, --block-type [sink|source|sync|decimator|interpolator|general|tagged_stream|hier|noblock]
                                  One of sink, source, sync, decimator,
                                  interpolator, general, tagged_stream, hier,
  --license-file TEXT             File containing the license header for every
                                  source code file.
  --copyright TEXT                Name of the copyright holder (you or your
                                  company) MUST be a quoted string.
  --argument-list TEXT            The argument list for the constructor and
                                  make functions.
  --add-python-qa                 If given, Python QA code is automatically
                                  added if possible.
  --add-cpp-qa                    If given, C++ QA code is automatically added
                                  if possible.
  --skip-cmakefiles               If given, only source files are written, but
                                  CMakeLists.txt files are left unchanged.
  -l, --lang [cpp|c++|python]     Programming Language
  -d, --directory TEXT            Base directory of the module. Defaults to
                                  the cwd.
  --skip-lib                      Don't do anything in the lib/ subdirectory.
  --skip-swig                     Don't do anything in the swig/ subdirectory.
  --skip-python                   Don't do anything in the python/
  --skip-grc                      Don't do anything in the grc/ subdirectory.
  --scm-mode [yes|no|auto]        Use source control management [ yes | no |
                                  auto ]).
  -y, --yes                       Answer all questions with 'yes'. This can
                                  overwrite and delete your files, so be
  --help                          Show this message and exit.

Note:- For more information regarding help-texts : click-documentation.

Addind a module in-tree

Here is an example of coding a click command:-

@click.command('newmod', short_help=ModToolNewModule().description)
              help="Source directory for the module template.")
@click.argument('module_name', metavar="MODULE-NAME", nargs=1, required=False)
def cli(**kwargs):
    Create a new out-of-tree module

    The argument MODULE-NAME overrides the current module's name (normally is autodetected).
    args = DictToObject(kwargs)
    except ModToolException as err:
        print(err, file=sys.stderr)

Here the available options with the command are srcdir and all the options that the function of the class ModTool, common_params, adds to it.

So, to add a module in-tree, all you have to do is create module as with a function cli() in the modtool directory, add options and arguments to it with @click.option() and @click.argument() decorators and specify the functional details with the obtained value of parameters.
Note: Instead of **kwargs, we can specify the particular options.