A couple different thoughts:
1. You *might* be able to improve the response using a DAQmx Read property node set to configure "Advanced-->Wait Mode". It appears that the "Poll" setting is the most likely one that may help you to get a better response time (at the expense of burning CPU while doing the polling). "Yield" or "Sleep" are other options you might experiment with, but with "Sleep" you'll also need to specify "Advanced-->SleepTime".
2. Another possibility is to take a different approach to the problem. By doing unbuffered measurements, each Read will want to wait for the next full freq interval or the specified timeout. So there is going to be a guaranteed measureable execution time for doing the reads. There will also be a latency time as you cycle through each channel 1 by 1 before you can use those new measured values. The point is, you won't really get instantaneous 0-latency data no matter what.
So, another approach is to perform buffered measurements and simply query the buffer to read the most recent measurement already waiting in the buffer. Then the Read call will never be waiting for new data. There will be some latency between the time when that value was buffered until the instant you do the Read, but generally less than you'd have gotten with the unbuffered approach.
A. Problem 1: Only the first 3 buffered counter measurements can use DMA for buffering data. The next 2 will need to be manually configured to use Interrupts, which can be a bit of an issue for measuring higher freq signals. This is only a partially educated guess, but my confidence in such an approach would start to decrease as the measured frequencies increased above maybe 10 kHz. (If you are well above 10 kHz, it may be better to measure the freqs by counting edges per 10 msec interval or something like that. Then you'd have no problem with the buffering rate while still getting decent resolution.)
B. Problem 2: You'll need to use the DAQmx Read property node to set yourself up to read "the most recently buffered sample". Set RelativeTo=MostRecentSample, Offset=(-1) and then when you call DAQmx Read, just request 1 sample.
-Kevin P.
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