Forum: GNU Radio About sample lost

67a94b01740ab1e799a0508a064c5c09?d=identicon&s=25 Zan Li (Guest)
on 2013-06-04 09:26
(Received via mailing list)
Dear list,
Now I meet a problem about counting all the input samples.  I hope I can
get some assistant from here. The problems are as follows,
In one of my blocks, I want to count all the consumed input samples to
get
the timestamp of the received packet. I have used GPS to synchronize two
usrps and therefore for the same packet the two usrp should consume the
same amount of samples in this block from the beginning of the stream.
At
the very beginning, it works fine but after it works for a while the
timestamp in one usrp will lost 8192 samples (8192 samples less than the
other one). I have checked it is the same as the maximum output buffer
of
one block.

I want to ask if it is possible that because the block can not process
the
sample as fast as the output from the previous block, one buffer of
samples
are lost. BTW I did not find any indicator of overflow from uhd when I
run
the code.

Any suggestions would be appreciated.

Best regards

Zan
D7c45fe2b9d1bc4156cebeb19a3a2b63?d=identicon&s=25 Josh Blum (Guest)
on 2013-06-04 17:38
(Received via mailing list)
On 06/04/2013 03:25 AM, Zan Li wrote:
> one block.
>
> I want to ask if it is possible that because the block can not process the
> sample as fast as the output from the previous block, one buffer of samples
> are lost. BTW I did not find any indicator of overflow from uhd when I run
> the code.
>
> Any suggestions would be appreciated.

Any thoughts on my previous reply?
http://www.mail-archive.com/discuss-gnuradio@gnu.o...

Also, there is an API to get the number of samples consumed. In your
work function, you can all this->items_consumed(input_port_index). Just
in case you didnt know, so you do not have to do a manual count, the
scheduler will do this for you.

Also, what do you mean by "timestamp in one usrp will lost 8192
samples"? The timestamps are typically tagged on the first sample and
only resent when there is device overflow. So I am curious how you are
determining lost samples. Are you correlating on a shared pulse
transmitted into both USRPs?

-josh
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