Couple of (somewhat naive) questions here: > It's similar to asynchronous switching inside a digital computer. > You can > add levels of flip flops to synchronize across two asynchronous > time-domains, > but all you are doing is decreasing the possibility of a > meta-stable failure to > make it through the flops. Statistically you can never guarantee > that there > won't be a failure at all; even if the MTBF is 10 Million years > by using five > levels of synchronization etc, a failure could actually happen > after 10s of > operation.
Well, no, proper domain synchronization doesn't just give you an incremental advantage. The use of flip-flops between clock domains is done to trade latency for guaranteed stability. The idea is to isolate the effects of metastability to a single clock edge that won't be used to clock anything else. Unless a metastable event somehow lasts more than one clock period (or half-period) it won't constitute a failure... and that never happens in practice, in the absence of a hard failure. Correct? Or am I missing something? (e.g., are we talking cosmic-ray hits, which are much more likely to affect RAM elements than clock synchronizers?) > The good news is: there are mitigating factors. Most jumps are in > the E-011 > or E-010 range, and most applications won't even be affected by such an > extremely small frequency change, and we have GPS to quickly correct the > aberration. Is it a good idea to tie a crystal to GPS with such a wide loop bandwidth? GPS-locked loops are usually on the order of t=1 minute, right? Or do you use 'speedup' tricks to temporarily widen the loop bandwidth when you see a fast transition? That sounds reasonable as long as there aren't any GPS propagation aberrations or timing-receiver artifacts that can't be distinguished from a crystal jump. -- john, KE5FX _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
