Re: [Discuss-gnuradio] write a new block to split existing functionality

[Tom Rondeau]

On Wed, May 22, 2013 at 10:27 AM, Matt D <address@hidden> wrote:
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> Hello everybody,
>
> I want to create a block that displays some data made available by the
> decoder block OP25..  OP25 was authored in the olden days before GRC.
>  Then the program would display some traffic identification data on a
> tab but now that OP25 has been adapted for GRC, this tab has been lost
> and I want to bring it back.  So the task now is to split the existing
> functionality into a separate block to make it GRC friendly.  Talking
> about the C++ code in OP25 the author wrote:
>
> we have “data_unit objects that can be asked to take a snapshot of
> themselves creating a string describing their internal state that
> obeys the Python text serialization format. When Python decodes the
> pickle it gets a name/value map describing each of the fields.
> Currently we have the snapshot_du_handler send the pickle as a message
> and this may/may not be the appropriate mechanism for GRC.”
>
> The fist question I have do we need a different message-passing
> construct?
>
> Second question is what kind of block needs to be written? I thought
> maybe a sink, or probably better, a block with no inputs that just
> waits on messages.  But I don't want to haul off doing this and find
> out later it was the incorrect way to go.
>
> Thanks a bunch
> - --
> Matt D

If you can update to using the next branch (3.7), I would recommend
using ControlPort for this kind of feature.

There's some information on ControlPort on my website:
http://www.trondeau.com/home/2013/2/19/configuring-controlport.html

But we need to better document its use and how to set it up. Best to
just look at the examples (gr-blocks/examples/ctrlport) and tools
already available (gnuradio-runtime/python/gnuradio/ctrlport).

Also, I would suggest using PMTs
(http://gnuradio.org/doc/doxygen/page_pmt.html) instead of pickling
the data.

Tom



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