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From: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: inter-mode calls ?
Date: Sun, 07 Jan 1996 12:57:16 CST
Organization: Rice University, Houston, Texas
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Message-ID: <30f0178c.sandmann@clio.rice.edu>
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

> Is it possible to let a real-mode TSR make a indirect call to a p-mode
> function in djgpp 2.0b4 ? How can I obtain the address of this via-function.
> Any hints would be appreciated.

The answer is yes.  What you need is a RMCB (real mode call back).  See the
DPMI specification for more information.  There are helper functions available
in V2 which work to do this.  Actually, you can even write TSRs with DJGPP V2
since hooked HW interrupts get automatically reflected to protected mode (there
are disadvantages - like the DPMI footprint and stability, but it is possible).

By hooking a real mode interrupt with the RMCB seg:off, you can also have a
real mode interrupt call a PM function.