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Re: [Discuss-gnuradio] constant noutput_items

From: Michael Dickens
Subject: Re: [Discuss-gnuradio] constant noutput_items
Date: Wed, 28 Mar 2012 08:52:39 -0400

As Martin wrote, the shortest answer is: no, or, well, not really or not 
always.  Under some circumstances this could be made work at least sometimes, 
but I don't think you can guarantee it all of the time.  For example, many of 
the OFDM blocks always process exactly 1 packet's or FFT's worth of data, and 
hence have a guaranteed -actual- number of consumed and generated items; the 
amount provided and requested by the scheduler may be different that the 
actuals (and, I think, generally is).  IIRC, the technique used by these blocks 
is to set the I/O signatures, output multiple, and ::forecast such that the 
number of I/O items is a multiple of what is required (the packet or FFT 
length).  In my (very limited) testing, the OFDM blocks work for their defaults 
and sometimes other values; but they're not exactly robust -- some values just 
don't work (and, no, I cannot given an example off the top of my head; just go 
and play with the OFDM benchmarks).  Good luck! - MLD

On Mar 28, 2012, at 5:43 AM, Martin Braun wrote:

> Short answer: no. Long answer: It depends. If you're depending on the input
> items. For a source, or for a block independent on the input data,
> there's ways to do this.
> Also, you can fix the output item size. Perhaps that'll do what you
> want (i.e. you can output vectors of fixed length).

> On Wed, Mar 28, 2012 at 08:58:37AM +0100, s k wrote:
>> I want to ask that can we immobilize the noutput_items value to a constant
>> value when we write a block. So we can give always the same amount of output.

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