The problem is that there is very little description about the core

Not only you (see below), Based on what I have seen (and, in an instance, tried to use) I am totally off "free" IP.

extracted from http://www.embedded.com/showArtic...=166404172
The very low percentage of public-domain IP reuse suggests that "open-source" hardware isn't nearly as popular as its software counterpart. Developers are understandably wary of betting their expensive hardware project—potentially worth millions of dollars—on free circuitry. As with open-source software projects, free hardware IP is usually offered without any support. Unlike open-source software, hardware IP is usually difficult to modify and even tougher to verify. For most developers, it's well worth the cost to license commercially supported IP.

If, however, you actually paid for it, the old maxim applies : If you did not verify that documentation existed before you laid out the money - Tough!.

Erik