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Re: [Discuss-gnuradio] control of noutput_items by the user

From: Martin Braun (CEL)
Subject: Re: [Discuss-gnuradio] control of noutput_items by the user
Date: Tue, 4 Dec 2012 11:32:56 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Hi Zing Yu,

to be fair, this problem is not what you asked for in your initial post.

A couple of notes:
- The output buffer does not have to be "full" in order for the scheduler
  to call the following downstream block.
- Undeterministic latency is one inherent problem of GNU Radio
- 200 ms seems a bit much, though. Have you tried decreasing the buffer
  sizes between blocks? (Try set_max_output_buffer()).
- How many blocks are between your custom block and the UHD sink? Lots
  of blocks == lots of latency.


On Mon, Dec 03, 2012 at 11:21:29AM -0800, Zing Yu wrote:
> Hi Tom,
> What you have suggested is absolutely fine but it does not solve my problem.
> Actually, my custom block sends a burst of N samples whenever a condition in
> its code is met. Since that conditon is met pretty much regularly, I can say
> that the custom block sends a burst after every ~30 mS. Now, whenever
> noutput_items=2N are assigned to work() of my custom block, I observe that
> particular (to be transmitted) burst somehow does not get sent asap, rather it
> is sent after ~200mS. I have verified this by two ways:
> i) I receive the transmitted bursts at another node and measure the delay
> between successive bursts.
> ii) On the other hand, I time each bursts by means of tx_time_tag. Then, I do
> see that whenever noutput_items=2N, I see "L" printed in the console (which
> means packet is late and is discarded by the FPGA).
> So, in summary, I would like to send my bursts asap no matter what value
> noutput_items takes. Or, I want the scheduler to assign me exactly
> noutput_items=N items everytime. What do you suggest?
> Thanks,
> Yu.
> p.s.
> Alex,
> Could you explain a bit more how to accomplish what you have said? Thanks.
> ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
> From: Tom Rondeau <address@hidden>
> To: Zing Yu <address@hidden>
> Cc: "discu address@hidden" <address@hidden>
> Sent: Friday, November 30, 2012 7:24 PM
> Subject: Re: [Discuss-gnuradio] control of noutput_items by the user
> Yu,
> You don't always have to consume everything that's handed to you. So if you 
> get
> kN items, just process N of them, return N, then the scheduler will pass you
> the next N items in the buffer next time.
> Tom

> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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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