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[Discuss-gnuradio] GRC taps as parameter in hierarchical block?

From: Christopher Friedt
Subject: [Discuss-gnuradio] GRC taps as parameter in hierarchical block?
Date: Wed, 4 Mar 2015 14:54:49 -0500

Hi list,

I'm looking for a pointer in using GRC when creating a hierarchical block.

The hierarchical block has an parameter block of type None with ID
'taps'. The Value of the block is 'filter.firdes.root_raised_cosine(
nfilts, nfilts, 1.0, 0.35, 11 * samples_per_symbol * nfilts )'. nfilts
and samples_per_symbol are both also parameters. The 'taps' parameter
block evaluates properly.

The problem is, when I try to use the value of the 'taps' parameter
within a Polyphase Arbitrary Resampler block configured as type ccf
(Complex -> Complex ( Real Taps ) ), it does not evaluate the 'taps'
parameter. The 'taps' field is brown, which obviously means it does
not interpret the field.

Value "taps" cannot be evaluated:
    name 'taps' is not defined

However, when I use a Variable block for the exact same 'taps' value,
the resampler works properly.

Clearly the difference is that, with the variable block, the value is
evaluated at compile time, versus when using a parameter, it must be
compiled ... well... later at compile time... or at 'run time', if one
could call it that.

My question is, do any of the gurus on the list have a suggestion on
how to 'cast' the parameter as a real_vector or something equivalent
to make it usable as a block?

If it matters why I'm doing this, I'd like to make the
generic_mod_demod more generic by allowing the pulse shape filter to
be specified as a parameter... and yes, I'm doing it in GRC rather
than python for a few reasons.



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