Mill Computing, Inc. › Forums › The Mill › Architecture › Optimizing Mill System Design: The view from Low Earth Orbit › Reply To: Optimizing Mill System Design: The view from Low Earth Orbit
The Mill is by definition a SAS system, so the constraint on the low end is address space. A chip with no MMU (all addresses are physical) then that is effectively SAS, so if you can fit in that then you can fit in a Mill of the same size. On a 64-bit Mill the spillet matrix occupies 2^50 bytes of address, so the number of distinct thread and turf ids has to drop sharply as the space goes down, but for embedded the number of threads/turfs is probably statically known.
There’s also no architectural need for caches if you are going straight to on-chip memory. You’d probably want to keep the I$0 microcache anyway. The FUs and all the operand paths can have arbitrary width, but should probably not be less than pointer size to avoid code explosion. The predictor could be dropped if frequent misses are tolerable.
There are architectural overheads that are largely independent of address space and operand size: the specRegs, the decoders, others. As the Mill size shrinks these fixed costs start to be more important. It’s unclear when they would tilt a choice against the Mill.