At 09:28 AM 4/23/2007, Gene Heskett wrote: >Hi Greg & company; > >Is there available, for a reasonable price, a usb dongle that would >do nothing >but echo the packet back to the src so that some sort of a handle on the >latency could be measured/obtained?
I doubt one is available. You could reprogram any cypress fx2 high speed device to do it, I don't know what commercially available devices exist though. >Over on the emc list, we have a developer that wants to use emc, which >requires hardware response to such things as limit switch closures in at >least sub-millisecond response times else the machine, particularly if moving >at a high speed, might move far enough to destroy the switch (& maybe more >than that) before it gets stopped by the driving computer. 1) are you sure about the required speed. sub-millisecond is very fast. When I did a pinball machine years ago, a 5ms debounce was sufficient for the very fastest ball hitting a target. In the pinball machine, the requirement was more not missing a switch closure than detecting it quickly and doing something. However the debounce was done to catch the first closure and try to ignore later ones for a known amount of time (the target switch would vibrate open/closed rapidly). 2) With .5ms to 5ms what OS are you going to run on the host? It must be a rtos to guarantee response to an event. >This developer is already conversant with building usb stuff from the chipset >up, so the actual implementation doesn't seem to be a huge problem for him, >if the answer, in the 400 megabaud speeds of today, is a usable figure. High speed isoc IN and OUT could be fast enough over the bus, but refer to the issue in 2) above. >This question and issue is primarily driven by the gradual disappearance of >the std db25 parport hardware from the newer machines, the portables in >particular. > >We would like to be able to give a definitive yes or no answer to >the question >of "will it work?" In my opinion, USB under linux is not a good solution for very low latency requirements. I think a hardware redesign with intelligence in the gadget to prevent disasters would be much more sane. Regards, Steve ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
