[stella] 7800

Subject: [stella] 7800
From: Keith W Gerdes <kwg@xxxxxxxxxxxxxxxxxx>
Date: Fri, 13 Nov 1998 14:40:56 -0600 (CST)
> How similar is this "backdoor" to the trick used
> to make Lynx carts without Atari encryption?

Maybe this was a bad choice of a word on my part (we
don't want to start another 'encrypt' misconception),
but it seems to fit IMO.  :-)

As pointed out, it isn't similar at all.  Harry's card
has a valid key - and he had the foresight for himself
(and for others) to use a flexible design.

To circumvent the key check without a boot ROM mod and/or
to create a valid key is the real goal but there is that
workaround in the meantime.

One idea is to piggyback a valid 7800 cart.  With extra
circuitry, your cart would detect when to turn off the
other cart.  This was also mentioned for the Jag in rgvatari.
  7800 cart
  your cart

Another idea is to look at non-Atari produced 7800 carts-
Absolute, Activision and Froggo.  There may be a solution


> It still doesn't explain how Harry's cart passes
> the valdation test in the first place.

Harry sent the monitor to Atari and someone there ran
the key program for him, so it has a valid key. He
supplied full 2600 & 7800 docs and some 2600 games
with the monitor package with Atari's permission.

The trick is that he only specified the cart size as 4K.
This allowed him to make patches in the other parts of
the cart without bugging Atari for a new key.

> I have looked over the bios and don't see anywhere
> where you could steel control away from the bios
> before the validation check happens, short of
> putting some special circuitry on the cartridge.

True.  The question is how complex a 'hardware' solution
will be and which method is best.

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