"Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx> writes:
Does anybody know why we reserve this range of IO ports for 'fpu'?There are two ports used: 0xf0 is the busy latch reset and 0xf1 is the coprocessor reset. They are legacy ports resulting from the interesting way the FPU has been wired by IBM in their PC design.
AFAIK from all the IO maps I can find on the internet for various x86
chipsets only 0x00f0 is actaully ever used.
Was it really needed on 386s? I didn't think there was a IBM 386 PC.
AFAIK you are just right, I'm pretty sure there will be systems needing it for 386 and 486, and maybe the old Pentium systems as well. A lot of system vendors wanted it so software for the old systems would still work.
None of them is used by Linux for i486 and newer systems, which can support the FPU in its native configuration.
I can remove it from x86-64 at least.