Mill Computing, Inc. Forums The Mill Architecture Execution Reply To: Execution

Ivan Godard
Keymaster
Post count: 629

Congratulations! A remarkably complete summary.

The short answer is that there are no issue constraints in your example. However, because you are issuing loads and expecting immediate retire then you will get several cycles of stall between the load and con instructions; that’s why deferred loads exist, see the Memory talk for details. The data cache cannot get you data instantaneously.

More generally however, the operation set and hardware have almost no issue hazards. “almost” being the operative word here. An example of an issue hazard that does exist is FMA. While you can issue an FMA every cycle in all slots that support it, if you issue an FMA now and then try to issue a plain FP add in the cycle when the multiply part of the FMA is done then both the add and the add part of the FMA will be trying to use the adder hardware in the same cycle; no dice. The hardware throws a fault if you try.

And currently that’s the only case.