GNU Radio 3.9 OOT Module Porting Guide

The major changes in the (in-progress) GNU Radio 3.9 release that will impact OOTs are:


 * C++ modernization (C++11/14?)
 * Replacement of SWIG with Pybind11

C++ Modernization
(Currently merged onto master branch)

The most obvious change that will impact OOTs is that Boost shared pointers have been replaced with std:: shared pointers and memory management. At the top level of each block, the instantiation will need to change, e.g.

In include/blockname_xx.h:

typedef std::shared_ptr sptr;

Pybind11 Python Bindings
(NOT MERGED - future changes)

As of the GNU Radio 3.9 release, python bindings are handled using pybind11, which is inherently different than they were in previous releases

Dependencies

 * pybind11 &gt; 2.4.3 https://pybind11.readthedocs.io/
 * pygccxml https://pygccxml.readthedocs.io/en/develop/install.html
 * This is an optional dependency and basic functionality for OOT generation can be performed without pygccxml
 * It is required for automatically generating bindings for most of the GR source tree

Components
Python bindings are contained in the  directory

The bindings for each block exist in blockname_python.cc under the  directory. Additionally, a template header file for each block that is used as a placeholder for the scraped docstrings lives in the  dir

Comment Block
Each block binding file contains an automatically generated and maintained comment block that informs CMake when the bindings are out of sync with the header file they refer to, and what to do about it

In this case, the flag should be set to 0, and the bindings need to be updated manually. If the flag is set to 1, CMake will override the binding file in the source tree when it detects out of sync bindings. This should only be done in simple cases.

If a block needs pygccxml for the bindings to be properly generated automatically, this should be set to





Out-of-Tree modules
The steps for creating an out of tree module with pybind11 bindings are as follows:


 * 1) Use   to create an out of tree module and add blocks

Update the parameters or functions in the public include file and rebind with 

NOTE: without pygccxml, only the make function is currently accounted for, similar to

If the public API changes, just call  to regenerate the bindings

When the public header file for a block is changed, CMake will fail as it checks the hash of the header file compared to the hash stored in the bindings file until the bindings are updated

Build and install

Docstrings
If Doxygen is enabled in GNU Radio and/or the OOT, Docstrings are scraped from the header files, and placed in auto-generated  files in the build directory on compile. Generated templates (via the binding steps described above) are placed in the  directory and are used as placeholders for the scraped strings

Upon compilation, docstrings are scraped from the module and stored in a dictionary (using ) and then the values are substituted in the template file (using  )

OOT Migration
TBD

Caveats
Pybind11 bound methods do not implicitly convert int to enum, so blocks that take enum as input, must have either "raw" or "enum" in the grc yml definition of the block. "Raw" will allow the value to be changed by another variable in the flowgraph.

Block inheritance must be specified completely in the python bindings in order to use the inherited methods. For instance, if a block inherits from sync_block, both block and basic_block must be included in the inheritance specification of the class:

py::class_>(       m, "atsc_interleaver", D(atsc_interleaver))