First, friendly advice to help you help yourself. The info you just now provided is the crucial detail, but there was no hint of it in your earlier descriptions.
Speaking for myself (but expecting several others will at least nod along), I'm much more inclined to offer my time and help to someone who has obviously spent their own time being careful to describe their issue clearly and thoroughly right from the start. Some time to describe what you *want*. Some time to describe what you did, i.e., the things you tried and how you did them, including attachments of code when possible and sometimes data too. And then some time to clearly describe your observations of what you *got*.
Ok, back to your issue.
That long delay you see is a side-effect of buffering. There are at least 2 buffers to consider, and the general rule is that bigger buffers lead to longer delays. Here's a really good overview about output buffers (with emphasis on USB devices that need to involve a 3rd buffer).
First there's the task buffer that your calls to DAQmx Write interact with directly. For Continuous Sampling tasks, the buffer size is set by the # samples you write to the task prior to starting it. (There are also ways to size it explicitly if you choose.) The size of the task buffer affects how long it can take from the time you write until the data is delivered to the board. It's pretty much a high limit on the time. Depending on exactly when you write relative to what the driver is doing independently to deliver data to the board, the delay (also called "latency") may be shorter. When you want shorter delays, you make this buffer smaller. (When not using the default "regeneration" feature, this also means you must write more often.)
Second, your DAQ device has an onboard hardware FIFO buffer. The size available for this buffer varies greatly by specific device model. All data delivered by DAQmx to the board must travel through this FIFO before being generated as a real world signal. However, there are some advanced DAQmx properties available that can help limit how *much* of the available FIFO buffer gets used. It seems that some properties are only relevant & useful for a particular subset of devices -- you'll need to do some experimenting to discover what to use for your as-yet-unidentified device.
-Kevin P
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