Just FYI. I had trouble recently getting a 2Gig Registered DIMM to work with an MPC8541. The trick ended up being 2T timing. We were using 2T timing with a 1Gig non-registered DIMM.
However, 2T timing should never be used with registered DIMMs. The enable bits for 2T timing and registered DIMMs are OR'd together by the memory controller, and the result is used to enable a 1 cycle delay for certain signals when required. If both 2T timing and registered DIMMs are enabled, you would need a 2 cycle delay which the memory controller can't provide.
... Paul
