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Re: [Discuss-gnuradio] zero ninput_items_required[0]

From: Martin Braun (CEL)
Subject: Re: [Discuss-gnuradio] zero ninput_items_required[0]
Date: Tue, 22 Oct 2013 14:26:33 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Oct 22, 2013 at 02:20:04PM +0200, Nemanja Savic wrote:
> Hello guys again!
> Based on Martins suggestion and Marucs' explanation I copied some principles
> from sync_interpolator and situation looks much better. I used function
> set_output_multiple and set_relative rate and now the outcome of calling

FYI: When using sync_interpolator, it will call set_relative_rate for
you (that's why you specify an interpolation rate).

> forecast function is much better. For example, for symbol rate of 10k and
> sampling rate of 500k i get following:
> ninput_items_required 8, noutput_items 4000
> ninput_items_required 4, noutput_items 2000
> ninput_items_required 2, noutput_items 1000
> ninput_items_required 1, noutput_items 500
> ninput_items_required 8, noutput_items 4000
> And as u can see it always offers integer multiple of samp_rate/sym_rate. The
> problem comes now when i run the flowgraph with vector source that repeats the
> pattern. After calling forecast program executes work function but it provides
> me 32768 input samples which is of course silly:
> work function, ninput: 32768, noutput: 4000

Don't worry about that. In all sync blocks, the output buffer is what's
relevant. If you fill up the output buffer in this case, you will
consume 8 input items.
How are you even getting the number of input items?
sync_interpolator::work() doesn't tell you that.

It still seems like you're abusing the API somehow.


Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

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