Donkey Kong - Why is attract screen always the same in MAME?

[Zhorik]

Over on the CAG forums there's a thread where the question has come up of why after first starting MAME the attract screen for Donkey Kong always shows Mario and the barrels doing the exact same things. On an actual arcade cab after booting up MAME and letting it go to the attract screen the barrels sometimes take different paths/timing. Here's the thread http://www.classicarcadegaming.com/foru ... l#msg52237

Also note that in different versions of MAME the same things don't happen on the initial attract screen. For example in WolfMAME.106 Mario gets the hammer and kills several barrels before walking off the right side of the second platform. In WolfMAME.138 Mario just runs to the left on the second platform and walks into the first barrel he comes to.

One of the guys on the thread posted a video of what the attract screen actually did on an arcade cab after 6 different reboots: http://www.youtube.com/watch?v=TN6hoiPhrUM Note that none of the attract screen sequences in the youtube video match what happens in either WolfMAME.106 or .138.

I was wondering if one of the more technical folks here that is more familiar with the inner workings of MAME would know why this "randomish" behavior of an actual arcade cab isn't appearing in MAME? Barry, Kale, others, any ideas?

Thanks,
George

[Barthax]

There's no entropy involved with MAME so it repeats the same thing every time. On more modern games, the user can add [fake] entropy by hitting keys before inserting a coin or by inserting a coin at different intervals. The predictability of the MAME environment (i.e., completely fake) is what makes playback possible. I'd imagine (don't have proof) there's something left over from the previous session in RAM (it doesn't clear immediately, for example, like with an Atari ST or Commodore Amiga) or some other input checking involved that hasn't been emulated perfectly - something for the hardware guys to muse over.

[Edit:] Wierd, I thought this showed up on "View new posts" but it couldn't have considering its about a month old... I must have done something without thinking & gone browsing.