How many ports GRC enforces depends on the .xml file in your module's
grc/ folder, so you will have to add a
<optional>1/<optional>
to the respective <soruce> definition in your .xml.
Regarding operating on out1 iff there's a second output port:
you can either overwrite the check_topology()[1] method and memorize the
number of output streams, or you can just use the fact that work()[2] is
called with a
gr_vector_void_star
<https://gnuradio.org/doc/doxygen/gnuradio-runtime_2include_2gnuradio_2types_8h.html#acd3f499576e769966ea44554b359d949>
& /output_items/
which is but a typedef for a std::vector<void*>, which means it's a
vector of pointers to your output buffers. And hence, the number of
available output buffers is just
output_items.size().
You must NEVER write to out1=output_items[1] if there is only one
stream. That would be a bug, and in most cases actually lead to a
segmentation fault and cancellation of your program.
Best regards,
Marcus
[1]
https://gnuradio.org/doc/doxygen/classgr_1_1basic__block.html#aca13d6f083397aada5b44d0f349ce151
[2]
https://gnuradio.org/doc/doxygen/classgr_1_1sync__block.html#a38942c5d8bee5232404ab71ada9a3956
On 16.12.2015 23:40, Charles Bridger wrote:
> I've created a signal source and want to create a second port which outputs
> the same signal, except one sample behind. The problem I'm having is that I
> don't know how to make it "optional". If I change the code in the private
> constructor from:
>
>
> [Constructor Code}
> ...
> gr::io_signature::make(1,1,sizeof(float)),
> ....
>
> to
>
> gr::io_signature::make(1,2,sizeof(float)),
>
> It still makes me plug something into the port when I use the block in
> GRC, even when I don't want to use the second output port.
>
> I don't know if my code in the work method is relevant but I address the tw
> output ports like this:
>
> float *out0 = (float *) output_items[0];
> float *out1 = (float *) output_items[1];
>
> for(int i = 0; i < noutput_items; i++)
> {
> out0[i] = stuff;
> out1[i] = stuff - 1; // <- I want that to be optional when I put the
> block in GRC.
> }
>
> I've also tried setting the io_signature::make to 1,-1,sizeof(float) but
> that's less than ideal and doesn't work if in GRC i set number of outputs
> to 1.
>
> Again thank you all for your time.
>
> Cheers,
> Charles
>
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
> [email protected]
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