Normally all exceptions in MicroBlaze are precise, meaning that any instructions in the pipeline after the instruction causing an exception are invalidated, and have no effect.
When C_IMPRECISE_EXCEPTIONS is set to 1 (ECC) an Instruction
Bus Exception or Data Bus Exception caused by ECC errors in LMB memory is not precise,
meaning that a subsequent memory access instruction in the pipeline might be executed.
If this behavior is acceptable, the maximum frequency can be improved by setting this
parameter to 1.