Re: [stella] WSYNC and RESPx questions

Subject: Re: [stella] WSYNC and RESPx questions
From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 21 Aug 1999 17:19:41 +0200
At 10:55 21.08.99 +0200, you wrote:

>I have no access to hardware, therefore i'm testing
>everything on different emulators. They all allow WSYNC to
>start at cylce 74, but i'm not shure if this emulation is

IIRC if you start the WSYNC after cycle 72, you'll get an extra

>My second question is: what is the earliest usefull cycle
>for RESPx?

They all are usefull depending on where you want to position
the object. Hitting RESxx at any cycle before 22 will have the
same effect as hitting it at cycle 22 though. But this means
that you have more possibilities to position objects on the left
side of the screen, which can be usefull if your display kernal
is very timing sensitive.

>If you look at riveraid.asm again, you find a special
>routine for players on the very left side. The RESP1
>doesn't end at cycle 23, which would be correct in relation
>to the other possible values. It ends at cycle 25 and an
>extra HMOVE for 6 pixel to the left is done to correct
>this. I've no explanation why this is done that way, maybe

That's because of the HMOVE command right after the fist WSYNC.
If you access RESxx or HMxx within 24 cycles after a HMOVE
command, you might get different positions for the objects than
normal. Z26 emulates this effect except for most of the variations
on the Cosmic Ark starfield effect, which works by doing just this.

Ciao, Eckhard Stolberg

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