Intel's "redundant prefix issue"

Posted Nov 27, 2023 16:26 UTC (Mon) by farnz (subscriber, #17727)
In reply to: Intel's "redundant prefix issue" by paulj
Parent article: Intel's "redundant prefix issue"

That's not how reused functional units work in a CPU, though. You have a FROBBASHER functional unit, whose mode bits are set by the CPU in different ways in different implementations; so, in the SDME 20001, FROBBASHER takes its mode bits directly from microcode, while in the 20100 where the FROBBASHER is also used by non-microcoded operations, its mode bit comes from elsewhere, unless the microcode execution engine is in control in which case it comes from a hidden state register (not from the microcode), and you now have to document that hidden state register and how it's controlled by the system.