Re: A86: Hooking interrupt idea

To: assembly-86@lists.ticalc.org
Subject: Re: A86: Hooking interrupt idea
From: Dan Eble <eble@cis.ohio-state.edu>
Date: Mon, 3 Nov 1997 08:35:20 -0500 (EST)
In-Reply-To: <345D407A.14DC@minot.com>
Reply-To: assembly-86@lists.ticalc.org

On Sun, 2 Nov 1997, MrManson wrote:

> > What I was referring to was this:  Does it jump to 38H about 200 times per
> > sec, even if you're running an ASM program, with interrupts enabled?  If so, I
> > would think that it would _drastically_ slow it down, or that it would even
> > mess up the registers, etc...
> 
> yeah it seems kind of useless running it all the time, maybe a flag
> turns it off? then again its for protection in programs so maybe not
> 

The interrupt procedure should not slow it down much, since there's not
much to do to handle a timer interrupt.  Besides that, remember that the
processor runs at about 6 MHz, and instructions usually take about 7-15
clock cycles to run.  That's an instruction rate of about 500000 Hz
(right?).  Using even a couple hundred instruction cycles 200 times a
second is still less than 5% of the total instructions executed.

As for turning off the interrupts with a flag, you're right!  The DI
instruction disables interrupts by changing a flag in the processor.  The
            ^        ^
EI instruction does the opposite.

--------
Dan Eble <eble@cis.ohio-state.edu>
         (http://www.cis.ohio-state.edu/~eble)

"Behold, how great a matter a little fire kindleth!" - James 3:5

References:

Re: A86: Hooking interrupt idea

From: MrManson <joemama@minot.com>