Notes on the Pentium's Microcode Circuitry

Re:Notes on the Pentium's Microcode Circuitry by mmastrac on Monday March 31, 2025 @05:40PM (#43540290)

I'm curious if the register you see near the microcode ROM is potentially hooked up to MSRs -- it could potentially be a read or write buffer.

https://www.cs.cmu.edu/~ralf/papers/highmsr.html

> To the left of the MAR is a 32-bit register that is apparently unrelated to the microcode ROM, although I haven't determined its function.

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Re:Notes on the Pentium's Microcode Circuitry by kens on Monday March 31, 2025 @05:59PM (#43540433)

That register could be a Model-Specific Register; I haven't looked at it closely enough to see what it does. The Pentium is very complicated with 3.1 million transistors, so my reverse-engineering of it is essentially bits and pieces here and there.

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