Custom block overflow

Hi all,
I am encountering overflow errors in my custom block in GRC even for low
USRP sample rates of 500 Ksps. The flow graph goes like 4 USRP’s
connected
to the custom block. The block does matrix correlation and inverse. The
size of the matrix is 4x8. Any help?
Regards,
Saran

On 04.02.2014 18:46, sarankumar wrote:

Hi all,
I am encountering overflow errors in my custom block in GRC even for low
USRP sample rates of 500 Ksps. The flow graph goes like 4 USRP’s
connected to the custom block. The block does matrix correlation and
inverse. The size of the matrix is 4x8. Any help?
Regards,
Saran

Your flow graph is probably running too slowly. You could record IQ data
and try w/ offline data.

MB

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Also, since this is a very common mistake:
Maybe you have a throttle block in your flowgraph.
If that’s the case, remove it.

Greetings,
Marcus

(Um, how do you invert a 4x8 matrix?)

On 05.02.2014 03:52, Martin B. wrote:

MB

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Ok, I think don’t know why it overflows, but I get a better feeling
for your system :slight_smile: thanks.

So: You have four UHD sources in parallel, feeding your block’s four
input streams simultaneously, is that right? So, in that case, you
have a total sample rate of 2MS/s, which is more in regions where PCs
might be underpowered. You have to do a covariance matrix every 16s
on average; this is quite a lot, possibly, though I have no idea of
the complexity that involves when using armadillo.

Maybe, you are I/O bound; do you write data to your hard drive or do
something similar after processing?

I think Martin’s approach makes very much sense. Could you take the
four USRP sources, do a “streams to vector” and save that using a
file_sink? Do you still get overruns then?

Then, using file source and a vector to streams, could you process
your data offline and see if the would be sufficient for real time
processing?

Greetings,
Marcus

On 05.02.2014 10:55, sarankumar wrote:

[email protected] wrote:

Hi all, I am encountering overflow errors in my custom


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Hi,
There is no throttle block in my flow graph. The USRP source is directly
connected to the custom block.
In the custom block, I form a 4x8 matrix with 4 being number of USRP’s
and
8 is the number of samples from each of them.
Then I do cross co-variance of the matrix(4x8) with its transpose(8x4).
The
resulting 4x4 matrix is inverted.
I use Armadillo linear algebra package for the co-variance and inverse
operations. The computer is equipped with 8 Gig ram and gigabit ethernet
card.

Regards,
Saran

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