On 17 Sep 2012, at 12:23, Danny Price wrote: > On the topic of sync generators, I often don't bother making a periodic > pulse, I just set-it-and-forget-it with a single pulse, along with some > arm/pps logic to sync up boards. > > Are there any strong arguments against this somewhat lazy tactic?
I think it's ok, as long as you're not using lossy links between boards. In the early PAPER correlators, for example, there were XAUI links between the F and X engines that would (on occasion), drop a data word. By propagating the sync pulse, the X-engines could realign themselves with the datastream periodically. If you're on one local board then I don't think it matters much. It's sometimes nice to get a bit of visual feedback by placing the sync pulse out to an LED as a heartbeat signal to show that the board's clock is alive and locked. When you've got lots of boards in the rack, over time it's then easy to see which lights aren't blinking in sync. Jason
