[Nios II]: questions on "trap" and modelsim

Sylvian,

The multiply/divide stuff is executed in our default handler as the result of an "unimplemenrted instruction" exception, something different from a user trap. We do this so that we can maintain binary compatibility between different versions of the Nios II core... so if some code is compiled to call a hardware multiplier that doesn't exist (as one example), the unimplmeneted insrtuction exception gets generated and we handle the multiply in software.