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From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Video Overlay Card software?
Keywords: Apple IIGS video overlay software wanted
Message-ID: <1991Jan13.062844.26145@nntp-server.caltech.edu>
Date: 13 Jan 91 06:28:44 GMT
References: <14833@smoke.brl.mil>
Organization: California Institute of Technology, Pasadena
Lines: 45

gwyn@smoke.brl.mil (Doug Gwyn) writes:

>KansasFest an Apple employee demonstrated a 640x400 version of Finder (with
>a few remaining glitches, but mostly functional).

Sorry, but what you saw was a program that did what the voc400linedemo did --
it simply displays a 400 line screen and then waits for the system to crash.
I was a summer intern at Apple and talked to Dan Hitchens (the Apple employee)
and he told me the truth.

>>For a quick cheap Prodos-8 only demo, FTP to tybalt.caltech.edu

>Thanks.  When launched from GS/OS it worked but didn't return properly
>after termination.  A nice demonstation of the capability, though.

I warned you not to have GS/OS loaded.

Why it crashes: the extra video memory is an exact copy (scbs & palettes too)
-- a SHR page two -- in bank $e0. Unfortunately, GS/OS allocates space for
handle structures at $e0/6000 (right in the middle of the screen) early on
in the boot process (i.e. before any inits are loaded). I have a P8 program
that allocates a fixed non-purgable 16K block at $e0/6000 and manually changes
its user ID to zero (this is illegal, but otherwise the block will be nuked
when the O/S boots). It must be run before booting GS/OS. (Thanks to John
MacLean for the tip! I told Dan, hopefully he'll rail on the GS/OS people about
it. 5.0.4 still puts handles at $e0/6000.)

>>I can type up my current programming notes on the VOC if you want them.

>If it's not too much trouble, I'd appreciate it.  Is there some published
>work giving programming information?  The manual accompanying the card is

There's a tech book from APDA but according to Dan it doesn't mention any of
the neat registers on the card or the 400 line stuff.

> Well, actually, the requirement that the card be installed
>in slot 3 in a IIGS surprised me.  Is this a deficiency in the support
>software or does the card rely on something magical about the slot 3

The M2B0 signal is only available in slot 3. It's necessary because the bank
address isn't reliably available on the data bus during an expansion slot
access (mistake! but it's too late now).

Todd Whitesel
toddpw @ tybalt.caltech.edu