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Known Issues and Limitations

Lessons Learned

ROS Integration in GNU Radio OOT Blocks

During the creation of the ros-interface out-of-tree (OOT) module, we found difficulties to link this new module against the external ROS libraries. Actually, the compilation process run just fine; the problem appeared at run-time with the following Python message: AttributeError: 'module' object has no attribute 'ros_interface' The problem is due to improper linking against ROS libraries, which is fixed with appropriate directives in the CMakeLists.txt file in the root of the module as well as in the CMakeLists.txt file under lib/:

target_link_libraries(gnuradio-ros_interface ${roscpp_LIBRARIES} ... )

Similarly, we had to explicitly define the linking against the LZ4 compression library by creating a proper FindLZ4.cmake file under cmake/Modules/ and adding ${LZ4_LIBRARY} to target_link_libraries:

target_link_libraries(gnuradio-ros_interface ${roscpp_LIBRARIES} ${LZ4_LIBRARY} ... )

Making a GNU Radio OOT Block Behave like a ROS Node

When we converted the ros-interface OOT block into a ROS node, we found that the callback function to process incoming ROS messages was never called. This was because the ROS spin() or spinOnce() functions were never called since the ros-interface instance is not a standalone program with a main function to call them. We solved this by using an alternative version of spin(), called AsyncSpinner. Then, when the ros-interface block is instantiated, the asynchronous spinner is started in the background.

Miscellaneous