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

From: Jeff Long
Subject: Re: [Discuss-gnuradio] Source Block - Flow Control
Date: Tue, 14 Oct 2014 19:19:26 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7

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:


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.


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
            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?




            David Halls Ph.D.

            Research Engineer

            Toshiba Research Europe Limited

            32 Queen Square, Bristol, BS1 4ND, UK

            Tel: +44 (0) 117 906 0790


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