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From: slackey@bbn.com (Stan Lackey)
Newsgroups: comp.sys.atari.8bit
Subject: DLI's and other hardware
Message-ID: <34962@bbn.COM>
Date: 23 Jan 89 18:56:14 GMT
Sender: news@bbn.COM
Reply-To: slackey@BBN.COM (Stan Lackey)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 28

A short time ago, I posted that I was having trouble with DLI's; when I changed
the color regs and character set in a DLI routine, and depended on the system
VBI to restore them from the soft copy, I got significant flicker, both above
and below the line I was using the DLI on.  I then implemented a fast VBI
routine that always restored the color regs and the char pointer, but still
got occasional flicker.

The thing I neglected to mention was what turned out to be the problem:  I was
using a timer interrupt to track a trakball/mouse input.  The timer interrupt
frequency was quite high, interrupting several times per display interval. 
(I originally tried to use the VBI to track the trakball, but found that it
was much too slow.  Even moderate speed in moving the ball would cause it
to overrun.)

I am now using the Commodore mouse, in joystick-simulation mode.  It can be
tracked at VBI speeds, not very well, but it does eliminate the above problem.
I even eliminated the fast VBI routine, as it was no longer needed to reduce
flicker.

Has anyone had this problem?  Does it occur when the timers are used as sound
generators?  Is there a way around the problem [of fast timer interrupts
interacting with VBI/DLI's]?

Oh - I made a mistake in a previous posting.  My statement that using
the cbm mouse in analog proportional mode read on the Atari as the
highest pot value was wrong - it actually reads as the number 3 [where
the range is 0-228], regardless of mouse position.
-Stan