Quote:
Originally Posted by Daniel_LaFleur
First off, Joe, I want to thank you for this discussion thread. The information here will be invaluble to students that do not understand bus architecture / limitations (something I know a bit about   ) |
I hope that in the course of transitioning from the old platform to this new one, we can share the design decisions that led up to the ultimate design for the system that the students and mentors will work with. I think an understanding of how we made the choices we made will help them to make better use of the system.
Quote:
Originally Posted by Daniel_LaFleur
Our old controller gave us a 40ms slow loop (where we could write PWM outputs). Given that, the capabilities of USB 2.0 (even with latency) would be a dream. I wasn't suggesting USB for output control (even though, in some cases it's possible) but instead for data input from cameras and other sensors.
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I realize that you weren't asking for that particular I/O expansion. I was responding to the assertion that you made concerning the use of USB DAQ products in general with the cRIO. It is true that some slow control applications can use USB, but the typical application of that doesn't use cRIO as the primary controller. Instead, a single board computer or even a PDA will be used. As such, the typical high-speed, high-reliability applications that demand cRIO, can not abide a USB interface to the real world. That is the reason that the commercial cRIO has no USB port. We did put USB on an old model (
cRIO-9012) which supported mass storage devices like memory sticks at full speed (USB 1.1). There was no real demand to either make it USB 2.0 or to support other types of devices, so it was left out of later designs.
Because the cRIO for FIRST teams will fundamentally be a stock commercial cRIO, the addition of USB to the controller is not possible.
Quote:
Originally Posted by Daniel_LaFleur
Now my guess is that the cRio (I havent seen a datasheet on the base unit yet) uses either CAN, PXI or a PCI express bus (My guess is CAN bus). The FIRST demonstration (not really complete ) showed a single ethernet camera at 640x320, 15fps, full color. This (to me) didn't seem to tax either the ethernet port nor the bus/processor but is stated as the capabilities of the cRio. This is why I was looking for USB connectivity and webcams.
So I guess my question is ... is the ( FIRST configuration) cRio capable (framgrab and IR) of more than than 1 camera at this framerate? higher framerates at lower resolution? higher framerates at lower color? Multiple cameras (at all)? |
The cRIO does support CAN by using an
NI 9853, but it is not supported natively on the controller. The primary interface to the cRIO is Ethernet.
In the demo, the cRIO was not heavily taxed to simply stream the image back to the PC, and the Ethernet port certainly wasn't saturated. I imagine multiple ethernet cameras would be straight forward to get going if a switch were used to attach both of them. The real problem comes when you try to do video processing on the images. At that point, I think the processor in the cRIO will be very heavily taxed and the frame rate of processing will likely be significantly less than the rate that the images come from the camera. Naturally this depends a lot on what you are trying to do and how efficiently you implement it.
Cheers!
-Joe