GR 3.9 ImportError: generic_type: type "sink" referenced unknown base type "gr::hier_block2"

[Jessica Chen]

Hello all,

Just re-installed Ubuntu 20.04 LTS and GR 3.9 today. According to gnuradoi-config-info -v, I'm currently working with GR 3.9.1.0.

As a test, I wanted to build a simple FM Receiver, composed of just an osmocom source, DC blocker, and QT GUI sink. However, when I execute the flowgraph, I get the following error:

Generating: '/home/cvr/Documents/champ_fmreceiver.py'

Executing: /usr/bin/python3 -u /home/cvr/Documents/champ_fmreceiver.py

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/osmosdr/__init__.py", line 17, in <module>
    from .osmosdr_python import *
ImportError: generic_type: type "sink" referenced unknown base type "gr::hier_block2"

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/cvr/Documents/champ_fmreceiver.py", line 35, in <module>
    import osmosdr
  File "/usr/lib/python3/dist-packages/osmosdr/__init__.py", line 21, in <module>
    from .osmosdr_python import *
ImportError: generic_type: type "sink" referenced unknown base type "gr::hier_block2"

>>> Done (return code 1)

More about my system: I've been struggling with getting the GR 3.9 change to work with HackRF One for a while now, so this is a completely fresh system with just GR 3.9, librtlsdr, gr-osmosdr, libhackrf, and their dependencies.

Possible explanations:

- I installed things based on this guide: https://lists.gnu.org/archive/html/discuss-gnuradio/2020-09/pdfNp27msymbN.pdf, which specified to cmake gr-osmosdr with the /usr prefix. I'm not sure if that makes a difference? GR 3.9 says its block path is: /usr/share/gnuradio/grc/blocks, so it should be able to find any relevant block files.

- However, the configuration file (/etc/gnuradio/conf.d/grc.conf) has a variable global_blocks_path set to "global_blocks_path = /usr/share/gnuradio/grc/blocks:/usr/local/share/gnuradio/grc/blocks". The /usr block path makes sense, but the /usr/local path doesn't. When I checked, no such path to gnuradio blocks existed in my system.

- A couple days ago, another user on this mailing list encountered a similar with a different block: "gr 3.9 OOT execution error: unknown base type gr::block" (https://lists.gnu.org/archive/html/discuss-gnuradio/2021-05/msg00035.html). I'm not sure if we're looking at the same problem.

Any help would be greatly appreciated.

Thanks,

Jessica