Peter Nachtwey
Member
You aren't getting it.
These wait states happen for every access of the USB interface. Every byte that is read or written will incur wait states. That means every byte transfered wastes a whole lot of time and the CPU does nothing else while waiting. I will try to find out tomorrow how many wait states our Profibus DP chip has and how many wait states the USB chips has.OK, I get the point - the basics, anyway. But I don't get any feel for how significant the effect is. It sounds like a millisecond/sub-millisecond wait, which could be significant for high speed/realtime devices like motion controllers and PLCs.
If one is willing to spend the money you can do what ever you want and get 32 bit access with zero wait states into a image table in dual port ram or dual port FPGA.Aren't you always going to have a similar delay, or can you get closer to achieving a "straight to the wire" I/O connection with any modern high speed connections?