Hardware-Timed Acquisitions with USB 6225?

[USB-sim5]

Hi,

    I am using a simulated USB-6225 to test some measurement studio software before purchasing a hub. I am trying to do a HW timed acquisition method, but when I attempt to configure that method with the DAQ assistant, it gives the following error.

Error -200077 occurred at DAQ Assistant

Possible Reason(s):

Measurements: Requested value is not a supported value for this property.

Property: SampQuant.SampMode
You Have Requested: Hardware Timed Single Point
You Can Select: Finite Samples, Continuous Samples

    I do not get this error when using a PCI 6225 simulated device, and was wondering if USB daqs do not allow for hardware timed acquisition, or if it may be because it is only a simulated DAQ.

Thanks for any help.

[Stuart_G]

This device does support HW timing.  You are just getting confused by NI's lingo.  If you do a Finite or Continuous acquistion it is doing "hardware timing".  You can set the rate of the onboard clock as well as the number of samples to read.  In both these modes we consider this to be a buffered, timed acquisition.  What you are attempting to do is HWTSP.  This means the acquistion is timed and the maximum number of points you can return at a given time is 1.  There is also special code in this mode to tell you if your reading/program is able to keep up with the rate you specified.  The typical use case for this mode is a real-time system where every single point is critical to the analysis/control.  For most applications though, buffered will work fine for you. 

The reason we don't suppor this on USB is because the latency and speed of USB is so horrible you would be lucky to get anything above say 500Hz-1KHz where with buffered mode you are going to be able to go much faster.  HWTSP is used mostly with our Real-Time offering which also doesn't support USB DAQ devices. 

My guess is the finite or continuous mode will be perfectly fine for your application.

Hope this helps

StuartG