Sprite multiplexing on PAL - wiki incorrect?

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Bananmos
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Sprite multiplexing on PAL - wiki incorrect?

Post by Bananmos »

So I remember a few years back there was a discovery that the PAL NES refreshes the OAM even in vblank after 20 scanlines to prevent decay.

And the wiki more specifically says:

"The 2C07 additionally refreshes OAM during the visible portion of the screen even if rendering is disabled. Because of this, OAM DMA must be done near the beginning of vertical blank on the 2C07, as everywhere else it will conflict with this refresh. In exchange, OAM decay does not occur at all on the PAL NES."

To me, that reads like the trick of OAM multiplexing to get 128 sprites on PAL just wouldn't work on a PAL console, because the OAM DMA would be equally inaccessible during forced blanking. Only the first 20 scanlines after vblank count.

But as part of a twitter thread about OAM multiplexing, I ended up running the NTSC version of Stunt Kids (the only game I know of* that does a sufficient amount of OAM multiplexing) on my PAL console. It runs fine on my PAL NES, and I couldn't see any sprite corruption taking place.

Screenshot and TV photo attached.

So it looks to me like the wiki knowledge might be slightly incorrect on this matter? Or worse yet, it might be PPU-revision specific :)

*RC Pro Am has two ROM revisions. The first revision combines an OAM DMA with susequent manual writes to $2004 to write only 8 extra sprites in total. The later revision just uses one DMA per frame... suggesting that maybe they removed this feature due to reliability issues. Because of the small amounts of sprites, it sort of doesn't count.

*Bigfoot is supposed to as vividly retold by Andrew Davie in an 20+ years old interview... but last time I checked I could not find any evidence of two OAM DMAs in Mesen's event viewer. It could again be a case of multiple ROM revisions
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stunt_kids_tv_photo.jpg
StuntKids_sprite_multiplexing.png
lidnariq
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Re: Sprite multiplexing on PAL - wiki incorrect?

Post by lidnariq »

Sorry, we discovered that's wrong but I failed to update the wiki because I have no idea what's right anymore.

Sour started a thread four years ago: viewtopic.php?t=15763 but I had no idea how to summarize the results.
Bananmos
Posts: 552
Joined: Wed Mar 09, 2005 9:08 am
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Re: Sprite multiplexing on PAL - wiki incorrect?

Post by Bananmos »

lidnariq wrote: Sat May 29, 2021 10:36 am Sorry, we discovered that's wrong but I failed to update the wiki because I have no idea what's right anymore.

Sour started a thread four years ago: viewtopic.php?t=15763 but I had no idea how to summarize the results.
Ah... thanks for the update! Still have never actually used a second OAM DMA, but it's nice to know it's compatible across both systems :)
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