CleverScope like framegrabber

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20 Jun 2009
Posts:

Hi,

I have got CleverScope with 4M and I am using Clever Scope like frame grabber (grabbing picture from camera). On trigger input I connected frame sync. on chanell A is connected line sync and video data signal is connected on chanell B. Camera's FPS is 30. What I know how to do is: grab one frame from camera to 4M memmory (on trigger event). But get this (picture) data from clever scope takes about one second. Is there a faster way how to get data from memmory or more ""continuously"".

My code is based on SimpleScope sample (from www.cleverscope.com).

Simply: Can I digitize (for example) 5 frames per second with 4MS for each frame?

Thank you very much.

Honza Sova

24 Jun 2009
Posts: 396

Hello Honza, sadly you cannot. First for a 4M cleverscope your maximum frame size is 2M, because you need two frames, one for capturing and the other for transferring. Each 'sample' of 2 channels + digital values is 4 bytes, or 32 bits. So 2M samples is 8M bytes. Our USB driver/PC implementation transfers at about 18Mbyte/sec real, so that means the 8M bytes would take 444 ms to transfer. Also we need to transfer (such is our design at the moment) the circular frame buffer to the flat transfer buffer. That happens at 14ns/sample = = 2M x 14ns = 28 ms. So we have lost 472 ms just in transferring. On top of that there are Windows latencies, and disk seek times to contend with. So we cannot transfer 5 frames a second of 2M (ie 10M samples/sec = 40 Mbytes/sec). If you can live with smaller capture sizes, then we cam manage 5 (or even 20) frames per second.
In addition, you can capture multiple frames (eg 5) to the acquisition unit memory at high rate. But they could only be 4M/6 = 660K samples each (5 for storage, and one for capture).

I hope this explains it.
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