Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wasatch!uplherc!wicat!keithm
From: keithm@wicat.UUCP (Keith McQueen)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Control-Break ignored in Turbo-C graphics mode....
Message-ID: <401@wicat.UUCP>
Date: 10 Apr 89 18:42:57 GMT
References: <89Apr4.202845edt.2759@godzilla.eecg.toronto.edu> <4212@ttidca.TTI.COM>
Reply-To: keithm@wicat.UUCP (Keith McQueen)
Distribution: na
Organization: WICAT Systems, Orem, Utah
Lines: 29

>In article <89Apr4.202845edt.2759@godzilla.eecg.toronto.edu> lansd@eecg.toronto.edu (Robert Lansdale) writes:
}	I have a small problem trying to get Control-Break to be
}recognized while in graphics mode, using Turbo-C's Hercules BGI driver
}(version 2.0). I initially revector the control-break handler to my own 
}handler using the ctrlbrk(handler) command, which works fine while in text
}mode, but is ignored once I switch over to graphics. I assume the
}BGI driver is vectoring the interrupt to itself. Any suggestions?

The problem is that control-break is only checked by DOS during I/O
and possibly at other key points during DOS interrupts.  When you
are in graphics mode, you have bypassed the DOS I/O and started
outputing directly to video RAM.

All is not lost, however.  The keyboard interrupt that recognizes
the actual keypress maintains a flag in low RAM that can be inspected
by a user program at key intervals.  The flag is kept at address
0:471 and is the high-order bit of the byte.  This bit is set to
a 1 when control-break is detected.  Your program can check it at
regular intervals and handle the situation accordingly.  Be sure
to clear the bit after you have handled things.


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