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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!wjh12!harvard!seismo!hao!noao!terak!doug
From: doug@terak.UUCP (Doug Pardee)
Newsgroups: net.micro.cbm
Subject: Re: clock vs joystick
Message-ID: <194@terak.UUCP>
Date: Mon, 12-Nov-84 15:18:21 EST
Article-I.D.: terak.194
Posted: Mon Nov 12 15:18:21 1984
Date-Received: Sat, 17-Nov-84 04:33:55 EST
References: <445@sdcsvax.UUCP>
Distribution: net
Organization: Terak Corporation, Scottsdale, AZ, USA
Lines: 28

> If any one has noticed that when the joystick is plugged in the user port 1
> and is pulled all the way to the left the clock cycles seem to be slowed
> down by a factor of almost 10? If any one has noticed this idiosync. of
> the C64 please post why. I will try and solve the little problem -
> 
> rich
> UCSD

Shooting from the hip...

No, I never noticed, but I'll speculate about the cause anyway.
Moving the joystick to the left is the same as pressing the
CTRL key on the keyboard.  The keyboard is scanned at 1/60
second intervals by using the 6526 timer interrupt.  The clock
is kept by counting 60 such interrupts as one second, etc.
A feature of the 64 is that holding the CTRL key down will
slow down screen scrolling enough that you can read it.

Now, for the Olympic event, conclusion broad-jumping.
The slow-scroll feature is probably provided by a delay loop
in the timer interrupt routine whenever the CTRL key is held
down.  This makes for a significant delay before requesting
the next interrupt, 1/60 second later, so that the 6526
timer interrupts are much less regular than 1/60 second.

Good luck chasing it down!

   Doug Pardee -- Terak Corp. -- ...!hao!noao!terak!doug