Re: [stella] 2600 Digital Clock (Demo)

Subject: Re: [stella] 2600 Digital Clock (Demo)
From: crackers@xxxxxxxx
Date: Sat, 4 Oct 1997 11:51:43 -0400 (EDT)
In article <199710032339.QAA10992@xxxxxxxxxxxxxxxxxxx>, you wrote:

>Is it running too slow because you have too many lines in the display?
>If the number of scan lines is not exactly 3 lines of VSYNC, 37 lines
>of VBLANK, 192 lines of picture and 30 lines of overscan, or some other
>combination adding up to 262 lines, your clock routine will be off.

I'll double check my display again but I'm pretty sure there's 192 lines.
I think maybe the problem might be with the Vblank and Overscan.

I'm using timers for both but of course I can't get the exact number of
cycles that each requires so I've gone with the closest number.

#$2C in TIM64T for the Vblank and #$24 for the Overscan. This ads a handful
of extra cycles to each and could be screwing up my clock.

Since the clock was slowing down by one second every minute I thought it
would work if after each minute I DEC SECS, and it seemed to be working
when I checked it against the second hand of my watch. So I left the clock
running to come back later and see if it was still keeping accurate time
and when I came back it had crashed. So I'll have to take a look and see
what was happening there.

Of course, for the Virtual Pet I don't really need a dead on accurate clock.
But I would like to have an accurate clock programme working just so I know
it can be done. I'll keep hacking away at this and see what I can do.

Can you have more than one timer running at a time on the 2600, or will the
INTIM register be confused? If you read the timer's status directly from the
timer itself (as long as you were careful to to have code that let it run
past zero) and didn't bother with the INTIM you might be able to have
overlaping timers running, right?

Maybe I need to run a clock that counts seconds from machine cycles instead
of frames. How many cycles are there in a second?

           (Time may change me, but I can't change time from hell!!!)


Accordionist - Wethifl Musician - Atari 2600 Collector | /\/\
*NEW CrAB URL* ***| \^^/
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