Ring acquisition with NI-IMAQ 1394

[Calv]

Our project requires saving captured images onto the hard drive with no frame loss, so Grab acquisition may not be sufficient. I wonder if there is a way to carry out ring acquisition with IMAQ1394 like that of the original IMAQ?

I was hoping to find equivalent functions of "IMAQ Configure List.vi", "IMAQ Configure Buffer.vi" and "IMAQ Extract Buffer.vi" in IMAQ1394, but none of them seems to exist.

"IMAQ1394 Get Image.vi" appears to be able to accept only one image at any one time, the option, image index, seems to be redundant to me. The example "Low-Level Sequence.vi" still runs after I removed the connection between the loop counter and "image index".

It is also unclear what the option, "no. of buffer" in "IMAQ1394 Configure
Acquisition.vi" could do. The example mentioned above uses multiple buffers, but nothing is connected to this option.

On a side note, I found that the buffering in IMAQ 1394 is not as logical as in IMAQ. Image(s) created along side the acquisition configuration would be used as its buffer frame(s) even though there is no connection between the two.

I would be very grateful if someone could share their ideas.

Regards,
Calvin Tsang
PS. I'm using IMAQ1394 version 1.1

[BruceAmmons]

Calvin,

This is one of the biggest problems I have had with IMAQ 1394. I was able to set up a continuous buffer, but there is no way to find out which buffer is the current one. The other problem with IMAQ 1394 is that it is software based instead of hardware, which means your CPU speed and operating system latencies can all affect it and make you miss frames.

What I ended up doing was making my own buffer, and using Grab to get each image. By checking the time elapsed between each frame acquired, I was able to detect missing frames. As long as the frame rates were low or I didn't update the display very often, I rarely missed frames.

My basic conclusion is that IMAQ 1394 is much better for snapshot type applications. Applications that require
continuous video with no missing frames work much better with the IMAQ boards than 1394.

Bruce