alt Hacker NewsI started reading this to understand Open Bus, which was capitalized in the title, so I assumed it was a proper name for some old bus protocol/standard that I'd never heard of.
After reading, I realized that he just meant that the bus was "open" as in not connected to anything, because the address line decoders had no memory devices enabled at the specified address ($2000).
It's pretty funny that the omission of the immediate mode (#) went unnoticed until the obsolete emulator didn't behave in the same way as the real hardware when reading <nothing> from memory.
His solution of changing the instruction to use immediate addressing mode (instead of absolute) would have the consequence of faster execution time, because the code is no longer executing a read from memory. It's probably now faster by about 2us through that blob of code, but maybe this only matters on bare metal and not the emulator, which is probably not time-perfect anyway.
Replies
Rare has a history of video games that work in testing and have bugs buried in them for years until some novel architecture surfaces them. Not to imply other companies don't; just that Rare is an easy-to-reference name on the topic.
Donkey Kong 64 has a memory leak that will kill the game after a (for that era) unlikely amount of contiguous time playing it (8-9 hours, if I understand correctly). That was not caught in development but is a trivial amount of time to rack up if someone is playing the game and saving progress via emulator save-state instead of the in-game save feature.
(Note: there is some ambiguous history here. Some sources claim the game shipping with the Memory Pak was a last-ditch effort to hide the bug by pushing the crash window out to 13-20 hours instead of 8-9. I think recent research on the issue suggests that was coincidence and the game didn't ship with either Rare or Nintendo being aware of the bug).
> It's probably now faster by about 2us through that blob of code, but maybe this only matters on bare metal and not the emulator, which is probably not time-perfect anyway.
(Some) SNES emulators really are basically time-perfect, at this point [0]. But 2us isn't going to make an appreciable difference in anything but exceptional cases.
[0] https://arstechnica.com/gaming/2021/06/how-snes-emulators-go...