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HimemSX Issues (Announce)

posted by Khusraw E-mail, Bucharest, Romania, 22.10.2020, 21:52

Jack has asked me to convey the following message:

> HimemSX as written has some SERIOUS "issues". Its "block move"
> call cannot be used in "V86" mode, or the PC will CRASH! Aside
> from DOS Extenders or packages like DJGPP, "regular" DOS systems
> still use either real-mode or "V86" protected-mode set by JEMMEX
> or JEMM386. Many users may be VERY upset at losing "V86" mode!
> HimemSX's "block move" function also uses 8K-byte "move windows"
> during which it goes in-and-out of the mode which handles "high"
> XMS memory. This is also done in a normal XMS driver for real-
> mode moves, that require a switch to protected-mode (or "unreal"
> mode) to move XMS data. But, 8K-byte blocks are NOT needed for
> "V86" moves, since JEMM386/JEMMEX "know how" to leave interrupts
> ENABLED across the entire move!
> And what about "special" drivers, e.g. XHDD? Since 2007, UIDE/
> XHDD have called the XMS manager only to "get" memory or enable/
> disable the "A20" line. All actual XMS moves are done by logic
> in the caching drivers, as any XMS manager must do lots of ERROR
> checks on every XMS request. Such checks DESTROY speed and are
> never necessary, after a driver has been DEBUGGED!
> What is needed is to update the "Int 15h, AH-87h" request within
> JEMM386/JEMMEX to support "high XMS" memory. If done properly,
> DOS systems will NOT lose "V86" mode, and "special" drivers like
> XMGR or XHDD should need only minor changes (adding a "high XMS"
> page number, etc.). This minimizes the changes needed in other
> drivers (XDVD2, RDISK, etc.) and programs which do "call the XMS
> manager" for XMS moves, thus reducing their own logic.
> I would accept updated JEMM386/JEMMEX drivers with such changes.
> And I would accept updating XMGR/XHDD to work with such drivers,
> also updating XDVD2/RDISK to call an updated XMGR, HimemSX, etc.
> which issue updated "Int 15h, AH-87h" requests, then let JEMM386
> or JEMMEX handle the actual protected-mode move, as they do now.
> But unless it is only a "proof of concept", HimemSX is the WRONG
> place to do "high XMS" moves! XMGR and XHDD will NEVER give up
> 13 years of FAR more general-purpose logic, "V86" protected-mode
> and MUCH faster speed, only to use HimemSX as it is now written!
> One can expect MANY other DOS developers might feel the same!
> Jack R. Ellis

---
Glory to God for all things

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