Re: [libdc1394-devel] Odd relationship between external trigger and framerate

[Johann S. <j.s...@ir...>]

Jon Schewe wrote:
> 
> Something I've discovered when working with a couple of different
> cameras from Point Grey Research and Prosicilia.  
> 
> When using an external trigger, I still need to call set_framerate on
> the camera, otherwise I don't get images.  The framerate set must be a
> supported framerate for the camera (as expected) and the framerate needs
> to be higher than the rate the external trigger pulses at or you don't
> get the images you expect.  So if I have the framerate set to 7.5 and
> try and trigger at 10, I get images at something less than 7.5 depending
> on the offset.
> 
> I see this with standard modes and with format7 modes. Is this behavior
> expected?

Yes.  The "framerate" you set on the camera is a misnomer.  It is 
actually the rate at which images are transmitted to the computer 
(bytes per packet).  If images are transfered more slowly than the 
rate of external triggering, then some external triggers will have no 
effect (depending on the camera firmware) because images are heaping 
up in the camera.

There is a similar answer to this issue in the FAQ which may also help.

Johann

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