Graph which scanline button press changes were registered. Quick and dirty implementation.
This is a riff on Pinobatch's "Telling Lys", but with a more detailed visual breakdown: https://gbdev.gg8.se/forums/viewtopic.php?id=580
This test program turns off the OAM copy during VBlank, however there is still the APA vblank interrupt running. So for better results:
- Turn interrupts off (display will look off): SELECT+DOWN
- Mash buttons
- Turn interrupts back on (display correct again): SELECT+UP
Results from checking FPGA clone behavior in the results folder.
Spoiler: they all seem to more or less match hardware. Emulators var, some try to mimic more entropy.
Some emulator differences to illustrate (running on Linux with a USB gamepad):
After reading a button press and plotting it on the screen, it discards the next button press as a lazy way to try and avoid vsync and hsync biasing due to safe vram access waiting. So it takes two button presses to get a single screen point.
A non-interactive mode that collects all the points and then plots afterward could be added.
Made in GBDK, requires the version of GBDK-2020 after 4.4.0 due to the use of SFR vars.