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Re: [Discuss-gnuradio] dynamically changing delay in gr_delay (or histor

From: Achilleas Anastasopoulos
Subject: Re: [Discuss-gnuradio] dynamically changing delay in gr_delay (or history in any gr_block)
Date: Wed, 16 Nov 2011 08:20:59 -0500

I can confirm that if my FIR taps are defined as:


then i can change the delay dynamically for any values between 0 and 19
in the grc file that i sent earlier (attached here as well) EVEN
without the second (trivial)
FIR filter present!

So it is clearer now that the problem with delay/filters is in the
setting of history...

thanks for the hints!

PS: Johnathan, could you give us a simple explanation of what happens
in the internals when there is a history change so that at least we
understand the computational model.

On Tue, Nov 15, 2011 at 11:19 PM, Johnathan Corgan
<address@hidden> wrote:
> On Tue, Nov 15, 2011 at 16:44, Marcus D. Leech <address@hidden> wrote:
>> But clearly, there's some brokenness there, and it's not clear to *me* how
>> to fix it, although I desperately want dynamically-settable
>>  gr_delay() blocks to work as well, for some interferometry work.
> Sorry, I've been buried in some commercial projects that haven't left me
> with much time to look at the issue more in depth.
> I can confirm that dynamically changing the delay in gr_delay does not (and
> never has) worked.  The fix for this is not that complex but it would be a
> change in the runtime that would need a lot of regression testing.
> In the FIR-based delay scenario, it would be useful to know if there is a
> difference between changing the taps from, say [0, 0, 0, 0, 1] to [0, 0, 1],
> so the taps end up changing length, or changing the position of the 1 but
> leaving trailing 0's so the tap length would remain the same.
> Johnathan

Achilleas Anastasopoulos
Associate Professor
EECS Department               Voice : (734)615-4024
UNIVERSITY OF MICHIGAN        Fax   : (734)763-8041
Ann Arbor, MI 48109-2122      E-mail: address@hidden
URL: http://www.eecs.umich.edu/~anastas/

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