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From: "Dijkstra" <pepitek AT gmail DOT com>
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Subject: Re: Need to hook INT 21h from a DJGPP TSR
Date: 8 Oct 2005 10:03:15 -0700
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Hi Rod!

Thanks for your examples. I'm also experimenting with other extenders,
namely DOS32A and WDOSX. The DOS32A is interesting since it seems much
more understandable (from my poor assembler perspective :-) From the
source code of DOS32A you can see it hooks INT 21h internally, so
unless I deeply modify the DOS32A source code, it's a bad idea to hook
it again. It can lead to many undesirable "PM" -> "RM" -> "PM Again"
chain loops.

So, I'm heading now into a diferent direction. I give up on the idea of
chaining INT 2Fh and 21h and make some kind of installable driver
instead. I will hook INT AFh and A1h (2Fh or 80h, 21h or 80h). They
will be real mode callbacks
(_go32_dpmi_allocate_real_mode_callback_iret) so that I could call them
from real mode. Then, I will code an additional pure real mode tiny TSR
that will be forwarding INT 21h and 2Fh safely from there.

I don't know if all this mess will work, but it will be a good research
work. :-)

Cheers,
Jose Miguel.