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Re: [Discuss-gnuradio] FIR filters and set_history()

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] FIR filters and set_history()
Date: Wed, 6 Feb 2008 07:42:51 -0800
User-agent: Mutt/1.5.17 (2007-11-01)

On Wed, Feb 06, 2008 at 02:11:00AM -0500, George Nychis wrote:
> Hi all,
> Sorry that this e-mail is long, but I'm trying to be as detailed as 
> possible for those reading it to understand, otherwise it will take a 
> couple e-mail exchanges.
> I'm attempting to build a filter using the fir filter class, but have some 
> questions.  Let's assume for a second that set_history() does not exist.

Hi George, the gr_fir_XXX* routines assume that the delay line is
"in-line".  This is, the delay line is implicit and that the calling
code (all the GNU Radio framework) does the right thing to ensure that
this is the case.

The history mechanism does work as it was designed to do.  For a
history setting of N, it effectively preloads the first buffer with
N-1 zeros.

If you've got a question about how it behaves, there's lots of QA code
for it. Take a look at filter/qa_gr_fir_fff.cc or _ccc.cc


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