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Re: [Discuss-gnuradio] Default value of "Taps" in GRC


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Default value of "Taps" in GRC
Date: Sun, 7 Jul 2013 04:43:56 -0400

On Thu, Jul 4, 2013 at 7:50 PM, Stephen Harrison
<address@hidden> wrote:
> The XML for filter_rational_resampler_xxx sets the default value of Taps to
> None. However, this gives the error Expression "[None]" is invalid for type
> complex vector.
>
> Deleting "None" from this box fixes the problem. Is it safe to change my XML
> definition to have no default value?

Stephen,

There is a bug filed on our Redmine Issues page about the use of '['
and ']' on different systems. I think this might be the same problem
you're seeing with the '[None]' instead of just 'None'.

The rational_resampler is a hier_block2 (in gr-filter/python/filter),
and if you tell it the taps are None, it will automatically calculate
a set of taps for you. It makes an allpass filter for the original
signal.

Off the top of my head, I'm not sure what happens if you leave this
block empty. It might be fine since the taps argument for this block
has a default of 'None', or it might think that the you are passing an
empty list of taps, in which case it wouldn't be correct. You can
easily test this by using the rational_resampler block as an integer
upsampler and looking at the output. If you see big images that aren't
being supressed, you aren't filtering.

My guess is that the latter is happening. If 'None' is being read as
'[None]', then I think '' will become '[]'.

Tom



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