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Groups > comp.os.msdos.programmer > #623

Re: Changing a DPMI host, but keeping the DOS extender

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Rugxulo  <rugxulo@gmail.com> wrote:
>I'm not sure of why some extenders choose which "type" of memory (API)
>to use. In other words, should it use XMS or EMS? Well, DOS/32A seemed
>to prefer VCPI/EMS despite my use of "NOEMS MAX=3D0".

VCPI exists primarily as a means to enter protected mode when an EMS
driver uses virtual 8086 mode to emulate EMS memory.  It's also necessary
when a driver is using virtual 8086 mode to create UMBs.  Since virtual
8086 mode is a form of protected mode a DOS extender can't simply enter
protected by setting the protected mode bit.  VCPI provides a way for
a DOS extender to gain full control of the CPU much like it would if it
was launched from real mode.

Note that whether or not DOS extender or DPMI host uses VCPI is a seperate
issue from whether it uses EMS or XMS memory.  HDPMI32 tries to use XMS
to allocate memory when using VCPI because apparently its faster that way.

>You're right, without VCPI, the DPMI host can't enter pmode, but it
>doesn't need to if DPMI is already loaded.

HDMPI32 still needs to use VCPI to enter protected mode after it's loaded
if JEMM386 is providing UMBs.  There's no other way to switch the CPU
to protected mode.

>I just switched off VCPI so it would be forced to use the preloaded
>HDPMI32. And that worked, then, under that environment.

HDPMI32 saved the VCPI protected mode entry point when it was made
resident and then used it later to enter protected mode when the DOS
extender started.  JEMM386 didn't actually turn off VCPI, it only
prevented it from being detected.  If HDPMI32 didn't save the entry
point or if JEMM386 had actually disabled VCPI completely then the DOS
extender wouldn't have be able to start.

					Ross Ridge

-- 
 l/  //	  Ross Ridge -- The Great HTMU
[oo][oo]  rridge@csclub.uwaterloo.ca
-()-/()/  http://www.csclub.uwaterloo.ca/~rridge/ 
 db  //	  

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Thread

Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-19 20:08 -0400
  Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-19 19:07 -0700
    Re: Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-20 05:38 -0400
      Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-20 09:15 -0700
        Re: Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-20 20:46 -0400
          Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-21 16:26 -0700
            Re: Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-22 03:39 -0400
              Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-22 08:41 -0700
                Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-22 16:14 -0700
                Re: Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-24 15:38 -0400
                Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-24 14:06 -0700
                Re: Changing a DPMI host, but keeping the DOS extender Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-05-25 02:14 -0400
                Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-25 15:55 -0700
                Re: Changing a DPMI host, but keeping the DOS extender Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-05-25 21:42 -0400
                Re: Changing a DPMI host, but keeping the DOS extender Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-05-25 22:06 -0400
                Re: Changing a DPMI host, but keeping the DOS extender Rugxulo <rugxulo@gmail.com> - 2012-05-25 23:03 -0700
                Re: Changing a DPMI host, but keeping the DOS extender "Rod Pemberton" <do_not_have@notemailntt.cmm> - 2012-05-26 07:33 -0400
                Re: Changing a DPMI host, but keeping the DOS extender Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-05-26 20:10 -0400
                Re: Changing a DPMI host, but keeping the DOS extender "Harry Vaderchi" <admin@127.0.0.1> - 2012-05-28 07:38 +0100
  Re: Changing a DPMI host, but keeping the DOS extender Ross Ridge <rridge@csclub.uwaterloo.ca> - 2012-05-20 19:20 -0400

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