[FieldTrip] A problem in real-time processing of MEG signal using field trip buffer

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Thu Feb 16 10:36:05 CET 2012

Dear Soheila,

we were facing the same problem here. Presumably, there is some problem 
in the shared memory module that the buffer is using. Right now, 
however, we could not find out where the error precisely comes from, so 
our best work around is to restart the computer prior recording and 
optimize settings, such as channels and sampling/decimation rate of 
acq2ft. In our lab, we managed to find near-optimal settings, so that 
the buffer crashes only rarely (actually, I never saw it crashing when 
the acquisition computer was freshly restarted). Note that a lower 
number of channels or higher decimation does not mean that it runs more 
stable.  It seems to be literally a trial-and-error approach :/

In order to track this down further, we need some more information, e.g. 
what MEG system are you using? What's your sampling rate, how many 
channels do you put into the buffer, and what's your decimation rate? It 
would be great if you could send me that information so that we can 
maybe try to track this down.

Best regards,

On 2/14/2012 5:42 PM, Soheila Samiee wrote:
> Dear group,
> I use FieldTrip for real-time processing of MEG signals using shared 
> memory and field trip buffer in a machine other than acquisition 
> system. I use matlab for reading the buffer and processing the data.
> During my data acquisition and sending it to other computer with 
> /acq2ft/ in linux, I face a problem. After sending some blocks of 
> data, this message: "/Internal Converter thread does not keep up with 
> load/" is shown in the terminal of /acq2ft/ and in my matlab session I 
> see an error : "ERROR: the buffer returned an error (517)". It does 
> not depend on sampling rate of data in acquisition system. The problem 
> often solve when I restart the computer which receives the data, but 
> after some minutes of transferring the data I see the message again.
> Would you please help me in solving this problem?
> Best Wishes,
> Soheila
> _______________________________________________
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> fieldtrip at donders.ru.nl
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Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

E-Mail: jm.horschig at donders.ru.nl
Tel:    +31-(0)24-36-68493
Web: http://www.ru.nl/donders

Visiting address:
Trigon, room 2.30
Kapittelweg 29
NL-6525 EN Nijmegen
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