Re: [stella] 2600 frying

Subject: Re: [stella] 2600 frying
From: Erik Mooney <erik@xxxxxxxxxx>
Date: Tue, 19 Apr 2005 00:18:32 -0400
On Mon, 18 Apr 2005 20:52:45 -0400, you wrote:

>Asteroids: Hold down RESET and fry until you see 2 asteroids on the right
>side of the screen.   Every game version will then have all white (slow
>moving) asteroids that start in the same spot and drift to the right, and a
>safe (predictable) hyperspace (youll always appear in the upper right
>corner).  All saucers will appear from the same spot (the upper left corner)
>and move straight across the top of the screen (the large one will
>continually shoot up while the little one will fire left and down).  Also,
>small saucers will appear around 7,300 points and continue to do so until
>the score rolls.
>Status: confirmed to work
>Atlantis: causes all ships to be the same type, and to fly from
>left-to-right only.  The Imagic logo will disappear and the game will start
>Status: confirmed to work

Interesting.  Both of those are almost certainly the random number routine
getting stuck on producing all zeroes.  Many random-number algorithms just
keep outputting zero if their seed state gets set to zero, including the
bit shift register style of algorithm that works well on the 2600.  This
could definitely be caused by RAM for the random number seed getting
cleraed while the 6502 either kept running or had PC reset to bypass the
usual startup init routine for the random numbers.

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