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Giving Back HMA ... (Announce)

posted by Jack E-mail, Fresno, California USA, 11.06.2010, 16:43

>> Ignoring older and more-obsolete versions, both V6.22 and V7.10 MS-DOS
>> have undocumented "issues" re: using HMA space ...
>
> I don't doubt your or Lucho's findings, nor shall the finding of one more
> MSDOS bug astound me :-) I've used MSDOS provided HMA since it existed
> (we're speaking sharing the HMA with the DOS kernel here, that is to say
> after "DOS=HIGH", not plain HIMEM/XMS HMA, right?) ...
Correct.

> ... but never been hit by bugs myself. Just a verification we're on the
> same wave length, and not to be taken as an insult, you're 100% sure you
> are using the local open/local close HMA calls systematically before/after
> jumping to your HMA code. Otherwise depending on the config, DOS "closes"
> the A20 line for compatibility with very old exepack'd software that could
> cause strange crashes when you try to jump to your code above 1024k. Just
> a wild guess.
UIDE uses exactly ONE run-time "A20 local enable", XMS request-code 05h, in
both its "Entry" logic for BIOS/"external" I-O and its "DevInt" entry logic
for SHCDX33E/MSCDEX calls to its CD/DVD driver. When UIDE finishes an I-O
request or if its BIOS logic "passes" a request, it then does an "A20 local
disable", XMS request-code 06h, before returning to the caller. Both such
calls are issued in UIDE's 944-byte "base" logic that always uses upper- or
640K DOS memory.

I am "rather-well aware" of what happens if one jumps up to the HMA without
issuing those calls correctly -- we in the U.S. would call it "Kissing your
[rear-end] GOODBYE!", i.e. CRASH!! UIDE has used those calls successfully
for 3 years! :yes:

---
(Account disabled on user's request.)

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