frederic-mahe / Analogue-Pocket

An issue tracker for Analogue's Pocket, a handheld FPGA device released in December 2021
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Mid-scanline Y Scroll register changes take effect too soon (CGB and DMG) #88

Open bbbbbr opened 2 years ago

bbbbbr commented 2 years ago

In both CGB mode and DMG mode on the Analogue Pocket (AP) writes to Y Scroll register (SCY, 0xFF42) take effect too soon vs original and some clone hardware.

In these two small homebrew demo samples there are 7 vertical sections which scroll at different speeds (tile widths: 4,2,2,4,2,2,4). On original hardware each section has uniform scrolling speed, but on the AP some of the sections do not have uniform scrolling speed (since the SCY writes are taking effect too soon and split the sections incorrectly).

DMG ROM

CGB ROM

canyon_vertical_parallax_test.zip