3 ms·
True, although microcode updates can still alter hardwired logic in a more limited way - it can’t fundamentally alter the logic, but (if designed to permit that
by skissane 3y ago
True, although microcode updates can still alter hardwired logic in a more limited way - it can’t fundamentally alter the logic, but (if designed to permit that) can reconfigure it - such as by disabling certain features. You just need some signals that change how the hardwired logic behaves, and a configuration register to feed them, and then allow the microcode to write to that configuration register.
- gpderetta 3y agoThey can alter the logic of instructions that are microcoded: it is literally the equivalent of a small program, with loops, conditionals, etc. Of course the ability to modify non-microcoded instructions is significantly smaller and limited to what was planned for at design time.
- dezgeg 3y agoYeah, I assume it's similar how ARM errata are often worked around - set some bit in an undocumented MSR to disable some microarchitectural optimization. A silicon vendor I worked at called them CYA (Cover Your Ass) bits :)