sorry about the delay Ive been fighting linux clusters,anyway my experiance with 8052 core is that if you want to implement every feature in a standard 8052 then the oregano core is ok as a standard implementation but it has no optimisation for any particular vendor and it will cause xilinx tools to crash which is not unusual for opencores I find.
The other extreme is the t51 single instruction 8051 compatable core which i have been looking at which is a very basic core with some interrupt support but with lots of peripherals missing.Its badly written and will cause the xilinx and altera tools crash as it stands,i have done some work on rewriting it but not got much further than adding a multiplier/divider unit and getting rid of some of the nastier code.If you look at the core at you wil find that its been written as something which will compile but I don't think that anyone has actualy tried to get it to synthesise to anything before.
Of the two the t51 has more potential to be of use to anyone,one of the problems with it is that if you add the mult.divide to the alu without the built in xilinx 18 bit multipliers of spartan/virtex family then you end up with a HUGE multiplier/divider which is a nightmare to fit.
All I can say to people who say that FPGA processors are not worth while is there are firms who make a living producing compatable cores because they fit niche markets.
Anyway ive got to get back to getting this freaking Mandrake cluster to work.
http://www.e.kth.se/~e93_daw/vhdl/