oam_dma_start.s does not correctly clear OAM

Gekkio / mooneye-test-suite

Mooneye Test Suite is a suite of Game Boy test ROMs

MIT License

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Closed LIJI32 closed 2 years ago

LIJI32 commented 2 years ago

The test accidentally clears a portion of VRAM rather than OAM, making the test non-deterministic on pre-CGB devices:

  ld hl, VRAM
  ld bc, OAM_LEN
  ld a, $D7   ; RST $10
  call memset

Note that fixing this memset changes the results of this test on hardware.

LIJI32 commented 2 years ago

Nevermind, it seems like I completely misread this test, OAM is shortly cleared soon after and my issue seems to be something else.