[USB]
> In my project it is important for me to get a command from the PC in
> constant time from the time that my PC program decided to issue such
> command. By constant, I mean less then 1mS.

Generic USB can't do this even for normal speed devices.  The most a device
is guaranteed is one packet per millisecond time slice.  The standard root
hub drivers also don't guarantee when this transfer will take place within
the millisecond.  The worst case latency is the therefore almost 2mS,
although typical average latency is much closer to 500uS.

However, if you use the right transfer mode and you know there are no other
devices on the USB bus, then can devise a scheme to get much shorter
latencies.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics