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Re: [Discuss-gnuradio] Source Block - Flow Control


From: David Halls
Subject: Re: [Discuss-gnuradio] Source Block - Flow Control
Date: Tue, 14 Oct 2014 20:07:24 +0000

Thanks guys!

I am transmitting data from a database, which is inserted by some sensors. The network is contains multiple relay hops and the processing at each relay is highly complex therefore the system o's not real time. The source transmits a data burst every 0.5 secs.

The issue is that the initial burst reads frantically and fills the buffers with the same value,  which then takes ages to propagate through the system.

does that make any sense?


-------- Original message --------
From: Jeff Long
Date:2014/10/14 20:20 (GMT+00:00)
To: Matt Ettus
Cc: GNURadio
Subject: Re: [Discuss-gnuradio] Source Block - Flow Control

Agree the throttle it not the best solution. David - what is your
source, and what problem are those 1000's of vectors causing at startup?

- Jeff

On 10/14/2014 06:08 PM, Matt Ettus wrote:
>
> Jeff,
>
> If there is a hardware device like a USRP in the chain, then you should
> not use a throttle block.  What you are seeing is the initial startup
> burst.  When everything starts up, all the buffers are empty, and GNU
> Radio will generate data until something backs up.  Once they fill up,
> you are seeing the rate settle down.  This is all normal.
>
> If you really need to rate limit what gets requested of the database
> during the initial transient (which I don't recommend), you should do
> that within your source block.
>
> Matt
>
>
> On Tue, Oct 14, 2014 at 10:56 AM, Jeff Long <address@hidden
> <mailto:address@hidden>> wrote:
>
>     Should have mentioned ... set the throttle rate just slightly higher
>     than what the chain would consume at steady state when all the
>     buffers are filled and the USRP is transmitting. How well this works
>     depends on what the rest of the chain looks like.
>
>     - Jeff
>
>
>     On 10/14/2014 05:52 PM, Jeff Long wrote:
>
>         Use a throttle block immediately after your source block,
>         setting the
>         vector size to match your source.
>
>         - Jeff
>
>         On 10/14/2014 04:34 PM, David Halls wrote:
>
>             Dear All,
>
>             I am wondering how to add some flow control to a source
>             block, so that
>             it doesn’t fire out items so quickly.
>
>             Later stages of my flow graph are slowed by various bits of
>             processing
>             and combining, before transmission via USRP, with bursts being
>             transmitted every few seconds.
>
>             What happens is that the block fires out 1,000s of vectors,
>             and then
>             seems to slow down and settle into sync with the rest of the
>             flow graph
>             after a few seconds. As my source block is reading in from a
>             Database, I
>             want to slow this initial rate significantly.
>
>             The block outputs vectors of bytes (v_len=144). Any ideas?
>
>             Regards,
>
>             David
>
>             ------------------------------__------------------------------__---
>
>             David Halls Ph.D.
>
>             Research Engineer
>
>             Toshiba Research Europe Limited
>
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