You can do it without *interruption*, but probably not without *latency*.
In older times, you couldn't write new data to a regenerating AO task but I was surprised to learn a few years ago that it had become possible. I don't really know when the support was added to DAQmx, I hadn't bothered trying for many years prior.
Anyway, you should be able to do 2 full-buffer writes back to back to accomplish what you need.
- write a full buffer that includes the ramp-down to zero from whatever was the last value in the original regenerating buffer. Pad with more zeros at the end if needed.
- write a second full buffer of nothing but zeros
- wait long enough to know that your ramp & zeros have worked through the task buffer and the device FIFO, then stop the task.
The amount of latency will be a combo of your task buffer size, where your generation task is within that buffer at the time you want to initiate the ramp-down, and the size & fill state of the device's onboard FIFO buffer (which is often configurable with DAQmx properties).
I've found that different devices use different methods to control the FIFO buffer. For some, it's a direct property to set the buffer size. For others, you get fuzzy control with the "data transfer request condition" which can be one of (less than full, half full, almost empty). There are yet other related properties that apply to USB-connected devices that I know less about.
-Kevin P
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