Changing the value of a Python Variable into a block

GNU Radio
1

Hello!

I’m developing a TV enconder, and I need to extract information from my
input data, and this will be used to determine the parameters of other
blocks on the flow graph.
How can I change the value of a variable of the python (or grc)
environment
from the block general_work() method?

Thanks!

2

On 01/24/2012 10:42 AM, Andr S. wrote:

Hello!

I’m developing a TV enconder, and I need to extract information from my
input data, and this will be used to determine the parameters of other
blocks on the flow graph.
How can I change the value of a variable of the python (or grc) environment
from the block general_work() method?

Well, you generally cant call a python function from c++… but heres a
few ways that may accomplish what you need:

  1. Using swig directors is a possibility. Rather than figure out the
    intricacies of directors, gnuradio already makes use of them in the
    gr.feval_* class, which you can use to call into a python object. Your
    general_work() calls the feval object in c++; and then feval object
    (from python) directly calls into other variables in the python-domain
    of your flow graph.

  2. Another possibility is passing messages into a message queue object.
    A python thread can pop the messages and act upon them.

  3. A related possibility, depending upon how your block operates would
    be to have a python thread periodically poll the getter methods of your
    custom block and act upon those values. There is already a block in grc
    that will poll another block’s getter function and update a variable.

  4. You could write the general work in python, which means all of the
    parameter calculation and setting occurs entirely in python (this
    functionality is not yet officially accepted).
    http://gnuradio.org/redmine/projects/gnuradio/wiki/WriteBlocksInPython

  5. And if thats not possible for performance reasons, you might consider
    a hybrid approach where you write general work in python, but you call
    into a function implemented in c++; where this function processes the
    input data and returns the “determined parameters”, which you can act on
    in python.

-Josh