Hi!
12-Янв-2005 17:46 [EMAIL PROTECTED] (Michael Devore) wrote to
[email protected]:
>>MD> Nothing on an application level should need to disable A20 and if it did,
>>MD> it would crash things loaded in a UMB due to loss of memory access, not to
>>--------------------------------------^^^ HMA ?
>>MD> mention DOS image loaded high going away. Most interrupts would
>>MD> immediately fail.
>> Why? They should fail only if they point into HMA and performed when
>>A20 is off.
MD> If you disable A20, then it's off, right? Important interrupts can go into
MD> DOS territory
But not neccessarily directly - there may be stubs in low memory, which
firstly tries to return state of A20.
MD> No HMA when an interrupt that goes there is triggered == bad
MD> situation. As I said, it was a decision made a long time ago before my
MD> time, you could research old discussions and talk with original developers
MD> if you want to know the exact reasons.
Of course, I remember discussions about handling A20 behavior. Only
main reason to support switching A20 off is bugs in MS exepacker (which was
used by MS link in many programs) and old PKLITE - they both behave
wrongly, when runs in first 64k of memory and there is HMA enabled.
MD> I don't think it affects anything important.
MD> As far as UMB's, I'm not sure if turning off the A20 line affects memory
MD> mapping from physical odd-address Mb. Seems like it should,
Michael, strange to see such sentences from you. A20 is a pin of (186
and higher) CPU, which used to pass 21th bit of address. When this pin is
disabled, all access with addresses like FFFF:200 (which make 21-bit
address) are "wrapped" (by ignoring high 21th bit on A20 pin) to first 64k.
This shouldn't affect any addressing in the UMB, which lies below 1Mb.
MD> but it would
MD> take time I'm unwilling to spend to create a definitive test. If A20 did
MD> affect it, that's another excellent reason not to support messing with it
MD> via application. Visualize a mouse driver going away.
>>MD> on my roadmap. May happen before March.
>> "May" == "can" or == "month May"? :) (Rhetoric questions, don't mind.)
MD> The context points to use of "may" being a verbal auxiliary for the
MD> intransitive verb "happen", as part of the predicate following an implied
MD> pronoun simple subject "It". (Yes, I had to look a lot of that up.)
Huh. For me, with my poor self-teached English, all above sounds as
mumba-yumba. :) But, Michael, sure, I understand what you wish to say, and
just note that your sentence for non-natives may _look_ as play on words.
MD> Aren't you glad you asked?
There was no ask, this was rhetoric question.
MD> Pool sharing coding will happen by the end of February, in the absence of
MD> unusual circumstance.
Will wait. :)
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