Global/Regional Clock Assignment

I also have been trying change some clock assignments, and I have also found that the fitter ignores some of the assignments. Some were honored. More disappointingly, there were no messages to explain how/why it is doing that.

I'm ending up taking a different tack - I suspect that part of my problem is a difficult clock crossing in the high perf DDR2 controller at full rate, and I suspect that if I use the controller at half rate, like the majority of people, that crossing probably is different, and an easier timing relationship.

Rule# 17 for using IP should be - are you using the IP in ways that are different from how most other people are using it? If so, you better have a good reason - actually, a reason that you absolutely can't use it the way most people do, because there are good chances you'll have trouble.