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.