News: 11 March 2016 - Forum Rules

Author Topic: Tracking Where to Write Tiles In VRAM  (Read 6488 times)

Disch

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Re: Tracking Where to Write Tiles In VRAM
« Reply #20 on: July 13, 2016, 04:18:31 pm »
What I meant was I assumed it kept repeatedly switching the bytes as if I mess with anything in RAM where the HDMA reads or even where the game regularly reads, it causes graphic corruption to occur, not that HDMA IS causing it, but the data being read appears to be read constantly.

Well it isn't read constantly.  HDMA only fetches stuff from RAM when it needs to.  But if you muck with the RAM before HDMA reads it, then HDMA won't do what you want.

Though the timing of exactly when HDMA does its reads is tricky to pinpoint -- so it's best if you just don't mess with the RAM at all until you know it's "safe" to do so (either by forcing blank, disabling the HDMA channel, or waiting until next NMI)


Registers on the other hand, are [in effect] read constantly.

justin3009

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Re: Tracking Where to Write Tiles In VRAM
« Reply #21 on: July 14, 2016, 04:47:45 pm »
Okay I think I got the better idea of it now.  Thank you very much on the understanding of it all!  I'll start studying all the details on what Chrono Trigger does and see if I can input something similar with Breath of Fire II.  I'll probably ask for advice and help on the way if I'm making any kind of progress with it.
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