From: Johann Schoonees <j.schoonees@ir...> - 2007-01-12 01:53:38
Kiran Kumar wrote:
> Im using libdc1394 on Linux OS for interfacing baseler602f camera. Im
> using external trigger to capture the images.
> Three aspects places major role in frame latency.
> 1. shutter integration time
> 2. frame transmission time
This is a slight simplification. There are actually two delays
between frame integration and reception: (1) sensor read-out time, and
(2) frame transmission time. It is unfortunately not so easy to
calculate the total delay because (1) typically depends on the height
of the image ROI (in Format 7) and because (1) and (2) may overlap
depending on the camera firmware.
Older Basler A602f cameras did not overlap sensor read-out and frame
transmission, but newer versions of the firmware do. This means
different performances from the same model of camera bought at
different times! Have a look at the sticker on the camera. If the
model name has "-2" after the "A602f" and the ID has a "-02" or bigger
at the end, you probably have the newer, faster firmware.
I have written a tool (using raw1394 and dc1394) which automatically
probes cameras to find out how they behave and what the various delays
are. It is most accurate if you trigger the camera from the serial
port (instructions on wiring in the source file) but it also works
without external trigger. I can send it to you off-list if you like.
> 3. computer scheduler (system tick) latency.
> To deal with the first one im using the shortest practical integration time.
> To deal with the second one I have set the number of packets per frame
> to a minimum
> Third one I have ignored it.
I don't know how to do this myself, but I believe that it is possible
(maybe at boot time via boot loader options) to select kernel
scheduler parameters that will affect latency. I vaguely remember
being told that most distributions ship with parameters set for
typical desktop use, and that there are alernative settings that
better meet the needs of real-time or embedded systems. I could try
to find out more if you can't google it.
> After doing this still Im getting 14ms per image. I want reduce it. I
> have one more doubt Im using VIA chipset is it the reason, or by
> changing National Instruments chipset can i achive the speed.
Hope this helps,
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