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 Post subject: Genesis 3 MMU bugfix?
PostPosted: Fri Nov 30, 2012 2:39 am 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 6304
Location: Seattle
Wikipedia said about the Genesis 3:
Wikipedia wrote:
due to a correction of a bug in the memory controller, some games which exploited this bug are also incompatible, namely Disney's Gargoyles
Is there a technical description of this bug? My google-fu is failing me.


edit: Wikipedia deletionists ruin everything.


Last edited by lidnariq on Thu Mar 17, 2016 6:32 pm, edited 1 time in total.

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PostPosted: Fri Nov 30, 2012 2:47 am 
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Joined: Wed Feb 13, 2008 9:10 am
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Location: Estonia, Rapla city (50 and 60Hz compatible :P)
TAS works "right" only on Genny3 VA2. VA1 behaves like any MD1 and MD2.

The thing is that TAS makes on unusual bus cycle that only fully completes on Genny3 VA2 and the instruction does what it is supposed to.
On MD1/MD2/Genny3 VA1 there is no writeback happening and the game relies on that, so the correct behaviour of G3 VA2 breaks games that dont expect the writeback to happen.

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