I've got my design talking to some (Kingston) KVR133X64/1G SDRAM modules and running at only 66MHz, doing some simple testing (the data=address or maybe data={address,address}) and have found some funnies.
There are a few dozen single bit errors. There are also several locations that come back with some F digits (as if the cells just don't exist). Also they are mid-burst as much as not which indicates it isn't a timing problem.
I have done testing on different FPGAs with different SDRAM modules and the errors definitely go with the modules and are quite repeatable.
I have checked the refresh timing and it's good.
Is Kingston SDRAM really that bad ? The fact they are made of repainted Infineon chips such that you can't read the original part number makes me suspicious that these might not be the real thing. They claim 100% testing but I wonder what they do with modules tested as bad. Is it because the FPGA can keep memory busy in a way a processor can't ? Should I speed up the refresh ? We intend to try some Micron parts anyway.
Jon