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Re: [Discuss-gnuradio] Limitations of gr_block: max_possible_items_avail

From: Martin Braun (CEL)
Subject: Re: [Discuss-gnuradio] Limitations of gr_block: max_possible_items_available = 8191
Date: Tue, 14 Aug 2012 14:53:36 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Aug 14, 2012 at 12:52:11PM +0200, address@hidden wrote:
> Hello,
> I created a block with a variable input rate, but when I run the flowgraph I
> get the following error:
> sched: <gr_block galileo_e1_dll_pll_tracking_cc (46)> is requesting more input
> data
>   than we can provide.
>   ninput_items_required = 16000
>   max_possible_items_available = 8191
>   If this is a filter, consider reducing the number of taps.
> If I don't exceed the limit of 8191 items the block works correctly but I need
> to exceed this limit for the experiments I'm doing.
> Is this a limitation of gr_block? Is there any way to exceed this limit?

I believe this is to do with the buffer limits between blocks (which are
set by the Linux kernel).

Do you *really* need this many input items per output item? If so, you
can also buffer manually, inside the block--here, there are no limits
other than the amount of RAM you have.

> In the other way I tried to use gr_sync_decimator but does not work because
> sometimes I need to consume 16000 ninput_items, sometimes 15999, and so on, 
> and
> gr_sync_decimator seems to have a fixed rate.

Yep, it's fixed. Use a gr_block, and use set_relative_rate() to
1.0/16000 or whatever.


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

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstra├če 12
Building 05.01
76131 Karlsruhe

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

KIT -- University of the State of Baden-W├╝rttemberg and
National Laboratory of the Helmholtz Association

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