Posted: Thu Apr 21, 2011 12:11 pm Post subject: X3-10M Capture small packets with Ext Trig in framed mode
I would like to accomplish the following with the X3-10M card:
Using the external trigger (in framed mode) run at 10KHz, capture 100 samples (at 20MHz) on each trigger with a delay of 5 usec.
I've read all of the documentation and many of the forum posts where others are interested in doing the same thing. It seems like an issue is that with small frames the interrupt rate is very high. Ideally one would combine several frames into one packet and send the packets at a slower interrupt rate.
Am I correct in determining that this is not possible using the stock Snap example or ApplicationIO implementation? It seems that packet size must be less than or equal to frame size.
Is there a straightforward way to solve this problem? In other posts I have seen the mention of developing custom logic. Is this necessary to accomplish this relatively simple task?
Joined: 07 Mar 2006 Posts: 2250 Location: So. Cal. USA
Posted: Thu Apr 21, 2011 7:55 pm Post subject:
This can readily be accomplished. To understand the solution, you must understand the difference between the frame size and the packet size.
Nomenclature: An event in one sample from each enabled channel.
The frame size controls the number of events acquired upon receipt of a rising edge on the trigger signal.
The packet size controls the number of events sent between the module and the host during data streaming. Each packet transfered results in an interrupt processed by the host CPU.
There is no requirement that the packet size be equal to the frame size. Configuring the packet to contain an integer number of frames is permissible and routine. For example, if the frame size were 100 and the packet size were 100,000, packets would be sent at 1/1000th the frame rate and the interrupt rate to the host would be substantially mitigated.
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