New option for number of samples per channel

[JB]

Screenshot from the help for number of samples per channel for a Read task :

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Please add an option for a continuous sample task to read all currently available samples (-1) but with a wait for a minimum number of samples (#min). Behavior of this configuration :

• #available samples >= #min : read all available samples
• #available samples < #min : wait until #min samples are available or until timeout

This would be very useful in several cases. For example :

• No extra coding to handle or avoid the error that appears if 0 sample is available.
• Avoid the use of a wait function in the loop to ensure a minimum number of samples are available.

[Seth_B.]

Functionality pretty similar to what you are describing is can be implemented pretty easily using the NI-DAQmx Read property "Available Samples per Channel"

Aside from the small increase in code, is there a reason this option won't work in your application?

[JB]

Thank you for your snippet !

Indeed this will work and I will use it. But some comments :

•  this solution uses (much) more space on the diagram (as you mentionned)
•  it needs additional code to implement a possible timeout
•  in most cases, it is necessary to put a delay in the False case to avoid a too high CPU usage
•  it is not obvious for beginners

Therefore I think it would be useful to implement all these functions in the DAQmx Read VI.

[Kevin_Price]

Here's the workaround I'd probably use.  You don't have to use CPU polling for # available samples,

and you end up with all available data when buffer holds > min #.

-Kevin P

[John_P1]

Depending on the context of the application, you might also consider an event-driven approach:

However... now that I think about it, the event fires every time N samples are acquired into the buffer so it doesn't quite give you the behavior you desire of obtaining a minimum amount of samples if you are doing multiple iterations.