Nios crashes when reading from the DDR2

Hey again,

Ok, so I have all the right timing now. But the Nios is still freezing up for some reason!

If I write 128 bytes to the DDR2 and read them back, it works fine. But when I try to write 256 bytes or larger and read them back the Nios stops working altogether. When this happens, in SignalTap I can see that none of the pio registers are being written to anymore, so that means the Nios just halted.

If I assume that timing to the DDR2 is correct, and that even if it wasn't it shouldn't be crashing the Nios, but just giving all F's -- what would cause the Nios to freeze up?

Andrew