Path: utzoo!attcan!uunet!aplcen!uakari.primate.wisc.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!nuug!hod!stud.cs.uit.no!borgen
From: borgen@stud.cs.uit.no (Boerge Noest)
Newsgroups: comp.sys.cbm
Subject: Re: Super Snap Shot Cart Detection??
Message-ID: <1990Sep26.111119.12057@hod.uit.no>
Date: 26 Sep 90 11:11:19 GMT
References: <+VJ%*-+@rpi.edu> <1990Sep24.162347.24968@jarvis.csri.toronto.edu> <449@news.nd.edu>
Sender: news@hod.uit.no (USENET News System)
Organization: University of Tromsoe
Lines: 39

In article <449@news.nd.edu> treesh@darwin.helios.nd.edu writes:

>I have heard rumors of really killer copy protection routines thaat use
>the video chip as a sync rigistar.  If a program is Snapshotted and then
>loaded, the video chip's timming will be off from the programs internal
>time keeping routines, and thus the copy is detected.  I have never seen
>code that could really pull this off, but I have heard about it being done.
> 
>Any comments welcome!
> 
>ctfm
> 
Hmm.. How about this:
These cartridges must have SOME problems with timing when they restart, so
how about having an interrupt that fixes the NMI vector(previously pointing
to a memory-clearing routine) and gets interrupted by the NMI before it has
time to return(tight timing), then the NMI routine does something (useful?)
and the NMI vectors are set back to the memory-clearing routine.

OR: Have an NMI routine that doesn't continue triggering - but sets itself
up for a new interrupt - (is this called one-shot ?) that fixes/destroys
something, which the rasterinterrupt continuosly undoes (with an INC?).
It could be possible to get values out of sync(perhaps giving a crash).

BTW, I have one of these cartridges myself. It's name is The Expert
Cartridge, and it has an off mode, an on mode, and a programming mode; the
last one is for loading in it's program onto a RAM-chip inside, which
afterwards behaves as ROM. The cartridge is triggered by NMI interrupts
through the restore key, but some programs seems to be able to disconnect
the restore key.
Does anyone know how to do this?
(Of course there is a HW add-on to stop these programs as well :-) )
Does anyone have any information on how to program it and use your own
programs?
-- 
_____________________________________________________________________________
|///  borgen@stud.cs.uit.no   (Borge Nost)   				 \\\|
|//   ...and then there was AMIGA...					  \\|
|/    studying at the worlds northernmost university			   \|