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

[David Halls]

Matt,

In my source block I can limit the calls to the DB ok, but I will still need to output something from the block, won't I? This will then propagate and fill the buffers?

Thanks, 

David

-------- Original message --------

From: Matt Ettus

Date:2014/10/14 19:09 (GMT+00:00)

To: Jeff Long

Cc: GNURadio

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

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> 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

32 Queen Square, Bristol, BS1 4ND, UK

Tel: +44 (0) 117 906 0790


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