Re: The latest instance in the A20 farce

["H. Peter Anvin" <hpa@transmeta.com>]

"Dunlap, Randy" wrote:
> 
> I'm not sure about this, but I'm wondering if the
> Fixed (as in Static) ACPI Description Table (FADT)
> can indicate that the platform is a legacy-free system.
> 

Parsing ACPI is a nightmare on steroids.  That is just Not An Option[TM]
in a < 10K bootstrap routine.

> 
> > Worse, they define that port 92h, bit 1, is no longer
> > A20M#... but they
> > don't forbid the system from using it for other things.
> 
> I don't quite see it that way.  Where do you see that?
> Maybe it just needs to be more explicit.
> 

It probably was *intended*, but it isn't *specified*, and in fact some
manufacturers have been known to abuse this bit.

> Ch. 3 (SYS-0047) says that port 92h:bit 1 doesn't toggle/affect A20M#.
> Appendix A says that port 92h is (still?) "System Control Port A"
> (not defined here AFAIK).
> (I haven't checked all of the other chapters/appendices.)
> 

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
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