Comment by rbanffy
11 hours ago
IBM’s microcode is really something. Not too long ago I heard about writing “millicode” as something that’s not at the microcode level, but not quite up at the ISA level.
11 hours ago
IBM’s microcode is really something. Not too long ago I heard about writing “millicode” as something that’s not at the microcode level, but not quite up at the ISA level.
Millicode used custom extensions to the ISA but is otherwise regular s390 code. For example there is a separate register file and the "original" registers are available with either (I don't remember exactly) special instructions or special memory addresses.
Intel by the way did the same for SGX, they called it xucode.