Part Number: PCM2901
Tool/software:
I can't comment on the original thread because the forum locks them. But I'm of that peculiar camp that finds it enormously beneficial when forums have both answers as well as questions, so am endeavouring to provide one.
Some weeks after reporting my challenges with intermitted device enumeration with a PCM2901 and a very close by device, I noticed something far simpler than the various possibilities we were exploring. I had failed to provide the required 15kΩ pull-downs that a hub must place on the data lines. This was enough loading to remove the flakiness, and so seems it may have been the root cause all along. Ain't that the way - don't neglect the basics.
See attached for an image of the layout that works, which can be compared side-by-side to the one in the original thread. The 22Ω array of series resistors is there, but a 15kΩ array of pull-downs has been added. No more flakiness. I did some minor path length tuning too as discussed, though I doubt it had much effect.
