Need help about the performance of RTW/RTAI/Comedi

wicky.zhang wicky.zhang at
Thu Jan 19 16:57:12 CET 2006

----- Original Message ----- 
From: "Roberto Bucher" <roberto.bucher at>
To: "wicky.zhang" <wicky.zhang at>
Sent: Thursday, January 19, 2006 1:49 PM
Subject: Re: Need help about the performance of RTW/RTAI/Comedi

> Hi Wicky
> we haven't reached such sampling frequencies till now, thus I can't say
> exactly what the problem is. First, you have to consider that a i386
> machine
> is not a DSP, you have ltencies which are greater than the DSP latencies.
> Paolo in Milano reaches sampling frequencies of about 40Khz, for special
> applications.
> Now, to your problem. I think that when you don't open the xrtailab
> application, the system works. Can you confirm it?

Yes, i have used oscillograph and signal generator to observe the input and
output of my DAQ card.

> Now, what happens if you run "xrtailab" on a second PC (with Linux RTAI
> installed, of course)? Do you have the same behaviour?

It will die when i run "xrtailab" on a second pc. My system have a target PC
with a remote PC for saving the resource of the target PC.
> If you don't have a second PC with Linx RTAI, you can try to install
> ( ) and monitor the RT task from a web
> browser.

Oh? it is a new idea. i have never notice it.

Thank you!

Best regards


> Regards
> Roberto
> On Thursday 19 January 2006 00:36, you wrote:
>> Hi Roberto,
>> Appologize for disturbing you again.
>> After trying many times and referring many documents, I can do nothing
>> about how to improve the performance of my simplest test demo (output
>> path
>> = a sine wave generator--->gain--->Comedi data write, while input path =
>> Comedi data read--->sfun_rtai_scope). The demo is based on
>> Matlab/RTW7.1(windows version)+RTAI3.2+Comedi0.7.70.  I tried NI6024E and
>> PCI9118dg of ADLINK both, the following is my test result:
>> 1: For 1 channel A/D,  the sample rate can be set up to 30KHz. But when
>> raised to 50KHz or higher, once using remote RTAI-LAB to connect the
>> target
>> system, the computer will not response the connection, even not response
>> to
>> either mouse or keyboard. The only thing i can do is to push the reset
>> button.
>> 2: For 6 channels A/D, the sample rate can be set up to 5KHz only. when
>> raise it, the same thing happens.
>> I have been suggested to check the cmd->flags|=TRIG_WAKE_EOS, which would
>> cause interrupt every scan, but i don't know how to set or clear it in
>> the
>> auto-generated code, even after reading many of the corresponding
>> documents, including rtai, comedi and Matlab/RTW.
>> I am wondering that whether the performance can be raised with the
>> auto-generated code? or should there be some tricks to improve it? I hope
>> my system can reach 10KHz sample rate with 6 channels A/D at least, can
>> you
>> give me some hints? thank you!
>> Best Regards,
>> Wicky
> -- 
> University of Applied Sciences of Southern Switzerland
> Dept. Innovative Technologies
> CH-6928 Lugano-Manno

More information about the Rtai mailing list