Re: [Discuss-gnuradio] ninput_items size problem

Hi,

Ramazan Çetin:
> I have digged some more.  This is how the connection is . OFDM MOD ->
> RATIONAL_RESAMPLER -> MY_BLOCK
>
> Everytime, 64 items remains inside of rational_resampler block. When my
> block is called by scheduler, i have logged the below. I am waiting 1950
> sized input for consuming. But resampler sends output up to 1886 = 1950
> - 64. This is always same, i  have tried for different sized tagged
> streams. It always sends up to "packet_len" - 64.

<snip>

> Why rational_resampler behaves like this? Please, help.

I think it is the history property of the rational_resampler block:

> void
> @IMPL_NAME@::forecast(int noutput_items, gr_vector_int &ninput_items_required)
> {
> int nreqd = std::max((unsigned)1, (int)((double) (noutput_items+1) * \
> decimation() / interpolation()) + history() - 1);
> unsigned ninputs = ninput_items_required.size();
> for(unsigned i = 0; i < ninputs; i++)
> ninput_items_required[i] = nreqd;
> }

history depends on the number of filter taps:

> void
> @IMPL_NAME@::install_taps(const std::vector<@TAP_TYPE@> &taps)
> {
> int nfilters = interpolation();
> int nt = taps.size() / nfilters;
>
> assert(nt * nfilters == (int) taps.size());
>
> std::vector< std::vector <@TAP_TYPE@> > xtaps(nfilters);
>
> for(int n = 0; n < nfilters; n++)
> xtaps[n].resize (nt);
>
> for(int i = 0; i < (int)taps.size(); i++)
> xtaps[i % nfilters][i / nfilters] = taps[i];
>
> for(int n = 0; n < nfilters; n++)
> d_firs[n]->set_taps(xtaps[n]);
>
> set_history(nt);
> d_updated = false;
> }

Documentation of the history property:
https://www.gnuradio.org/doc/doxygen/classgr_1_1block.html#a71548fe7804c9b932f9bb9d770931af1

> Assume block computes y_i = f(x_i, x_i-1, x_i-2, x_i-3...). History is the number of x_i's that are examined to produce one y_i. This comes in handy for FIR filters, where we use history to ensure that our input contains the appropriate "history" for the filter. History should be equal to the number of filter taps. First history samples (when there are no previous samples) are initialized with zeroes.

Cheers!

_______________________________________________
Discuss-gnuradio mailing list
Discuss-gnuradio@gnu.org
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio