Inconsistent behavior when running melonDS DS core

[jonko0493]

I'm currently part of a team making a homebrew DS game and we do some automated testing with libretro.py (fantastic work btw) and the melonDS DS core.

Part of the test involves navigating a menu that looks like this.

Relevant menu selection code is as follows:

uint32_t repeat = keysDownRepeat(), down = keysDown();

if (down & KEY_UP || repeat & KEY_UP)
{
    moveSelection(-1);
    return true;
}
else if (down & KEY_DOWN || repeat & KEY_DOWN)
{
    moveSelection(1);
    return true;
}

on melonDS standalone, melonDS DS launched through retroarch, and on console, this results in the expected behavior: pressing the down or up button once moves the menu selection down or up one item. after holding it for ~29 ticks, the "repeat" kicks in and runs again every 15 ticks. Image below depicts logging I inserted to demonstrate this.

When running the test in libretro.py, I'm doing the following:

# Enter debug menu, select first battle
yield JoypadState(select=True)
yield from repeat(0, 10)
yield JoypadState(down=True)
yield from repeat(0, 10)
yield JoypadState(a=True)

with the goal of selecting the second item from the menu. however, when doing JoypadState(down=True), the game registers a press and then a repeat a single tick later, resulting in the third menu item being selected rather than the second.

I've sent you the files for this on Discord. Thanks for your time!