On 11/30/05, Peter TB Brett <[EMAIL PROTECTED]> wrote: > > Timothy Miller wrote: > > > This sync fifo is intended to handle cases where there is no fixed > > relationship between the two clock domains. For instance, PCI might > > be at 33.333MHz and the other end of the FIFO might be going at > > 200MHz, but those are just approximate, and the clock generators are > > completely unrelated. That means there will be drift and jitter > > between them that will make the clock edges occur too close on a > > regular enough basis. > > Oops, sorry, on the projects I've worked on a 'sync FIFO' has been > synchronous in that both ends are clocked from the same clock -- so I had > the wrong end of the stick.
That's okay. I made up the name and didn't give it much thought. I called it that because in TROZ, we developed a 'synchronizer' that was able to move a piece of data safely between any two clock domains, and a fifo that had synchronizers in it to pass fifo head/tail back and forth were then called 'sync fifos'. Perhaps someone can suggest a better name? :) > > > I'm also being conservative because although I have some sense of > > what'll happen if the signals are register-to-register, I have no idea > > what will happen if you put combinatorial logic in between them. I > > think I'll just not take the risk. > > Yes, in this case I most certainly _would_ add an extra register in for > safety's sake, and suffer the small latency penalty. The latency penalty for this FAR less than what we did in TROZ. When going from 33MHz to 100MHz, the synchronizer would have a latency of 9 cycles. Part of that was because the synchronizer was TOO generic. Part of it was because I was transporting _binary_ head/tail, so we had to be more careful with it. Having only one bit change at a time with the gray codes helps massively. _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
