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From: ballerup@diku.dk (Per Goetterup)
Newsgroups: comp.lang.pascal
Subject: Problems with interrupt handler for interrupt 08 or 1C in TP 6.0
Keywords: interrupt, timer, turbo pascal
Message-ID: <1991Jan4.145541.17737@odin.diku.dk>
Date: 4 Jan 91 14:55:41 GMT
Sender: news@odin.diku.dk (Netnews System)
Distribution: comp
Organization: Institute of Computer Science, U of Copenhagen
Lines: 50


Hi everybody!

	I'm having some rather weird problems with a program of mine which
needs to get something updated on the screen no matter what else the program
might be doing.
	I'm using interrupt 1C (User Timer Tick) to call my procedure which
by the way DOESN'T call DOS (common error) - it only modifies the screen
memory.
	The problem is not to get it to work (it does) but what happens
next. I start it up by saving the old vector then re-assigning it to point
at my handler (procedure). This does indeed work and the screen get modified
as it should while my is running happily along. So far so good. Then
something might happen because sometimes the computer simply stops in the
middle of the program and lock up (refusing warm-boots), other times it runs
all the way to the end and then crashes when returning to either the DOS
prompt or Turbo's IDE (locks up again). At the end of my program I do
remember to reset the vector to the old value, and I even have an error
handler which does the same thing if an runtime error occurs. I also
remember to call the old interrupt handler at the end of my new one.
	I've then tried to use interrupt 08 (Hardware Timer) which btw calls
interrupt 1C during its processing. The result is the same. Crash on the way
or at the end. I've even had an error free run but at the next attempt it
crashed again. The conditions are always the same except the value of the
timer count (time passes!). This random behaviour really bugs me! - If it's
a programming error then it should occur at the same place every time - when
the conditions are the same, right? - And no, I'm not using anything random
inside the program WHAT SO EVER!
	Any ideas? - I feel I've tried it all, varying the compiler
directives (but always $F+ around the handler) and so on. I've tried to turn
interrupts on and off within the handler and sending an end-of-interrupt to
the CPU at the end of my handler - no change at all!. Naturally I've
checked both my program and the handler routine without using the interrupts
and they run perfectly!. No stack or range violations!

	Any hints or ideas would be most appreciated!

		Loads of thanks in advance!

			Per.

Reply by E-mail, but if it fails then please post your reply!

PS: I'm using Turbo Pascal 6.0 Professional as stated in the subject field.

-- 
| Per Gotterup                        | "The most merciful thing in the    |
| Student, DIKU (Dept. of Comp. Sci.) | world, I think, is the inability   |
| University of Copenhagen, Denmark   | of the human mind to correlate all |
| Internet: ballerup@freja.diku.dk    | its contents."  - H.P. Lovecraft - |