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From: Thomas_Hornschuh@p1.f36.n245.z2.fidonet.org (Thomas Hornschuh)
Newsgroups: comp.windows.ms.programmer
Subject: Re: Interrupts and high-resolution timing under Windows
Message-ID: <218197709@p1.f36.n245.z2.fidonet.org>
Date: 8 May 91 23:57:30 GMT
Article-I.D.: p1.218197709
Reply-To: Thomas_Hornschuh%p1.f36.n245.z2@hippo.dfv.rwth-aachen.de (Thomas Hornschuh)
Organization: Thomas Hornschuh, SoftStream 2, Dortmund (FRG)
Lines: 44
Comment-To: Oivind_Toien@f1.n6000.z2.fidonet.org (Oivind Toien)

OT> I have two interrupt routines that runs fine under DOS (Turbo-pascal).
OT> They both use the Setintvect function to attach Int $1C (the user
OT> timer interrupt) to an interrupt routine.
OT> 
OT> When running the same routine under TPW the debugger shows that the
OT> address is set correctly to the interrupt routine. But the routine does
OT> not seem to be activated. Has anyone has got this to work in either C
OT> or TPW? (If interest i can mail the source that works under dos).
OT> 

You can use the timer interrupt in windows. But you must install a protected 
mode interrupt handle with the help of the DPMI (DOS Protected Mode Interface).
DPMI is invoked via INT 31H.
You must use the functions

Name                             IN                       OUT
Get Protected Mode Int Vect.    AX=0204H,BL=Int Number.   CX:DX =
                                                          Selector:Offset of
                                                          handler

Set  "          "   "    "      AX=0205H,BL=Int. Number
                                CX:DX= Selector:Offset
                                of new handler             Carry flag = TRUE
                                                           if error

Using this functions is equal to the DOS SetInt/GetInt functions.
Don't forget to chain with a JMP FAR to the old handler at the end of your
new handler. 

An alternative is, use your old code as a DOS TSR, load it before windows and 
use the DPMI functions to pass control and data between your windows app and 
the TSR. But this is more complicated and only usefull if your old code can't 
run in protected mode.

The full DPMI specification can ordered from Intel, Santa Clara.


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