DVDInterface: Increase the latency for read commands

[JosJuice]

Hardware tested using cached reads.

Fixes Ed, Edd n Eddy (untested). https://bugs.dolphin-emu.org/issues/10373

[iwubcode]

This line seems to indicate there was a hardware test before. Any idea what changed?

[JosJuice]

If I'm understanding it correctly, the earlier hardware test determined that 300 µs was the fastest that any command can complete. This is a more complex command, so it makes sense that its latency would be higher than the latency of the simplest command.

[iwubcode]

Hmm, I guess we can only ever approximate this. What effect does this have on games that don't need this change? Longer load times?

[JosJuice]

Yes, but just a tiny bit.

[Tilka]

Tested and confirmed working. Previously the loading screen for the first level would get stuck and now I get into the first level.

[Pokechu22]

I can confirm that this allows getting into the first level; however, after getting into the first level, if I then pause the game, select options (by pressing right), and then select "Exit to Cul-De-Sac", the game freezes. The following is put in the log (I don't always get the invalid read part):

21:00:967 Core\PowerPC\PPCCache.cpp:192 I[PowerPC]: ICache read at 00da813c returned stale data: CACHED: 83c10020 vs. RAM: 9421ff68
21:00:967 Core\PowerPC\PPCCache.cpp:192 I[PowerPC]: ICache read at 00da8140 returned stale data: CACHED: 83e10024 vs. RAM: 7c0802a6
21:00:967 Core\PowerPC\PPCCache.cpp:192 I[PowerPC]: ICache read at 00da8144 returned stale data: CACHED: 38210028 vs. RAM: 91c10050
21:00:967 Core\PowerPC\PPCCache.cpp:192 I[PowerPC]: ICache read at 00da8148 returned stale data: CACHED: 4e800020 vs. RAM: 91e10054
21:00:968 Core\PowerPC\Jit64\Jit.cpp:784 W[PowerPC]: ISI exception at 0x6f693a70
21:00:978 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x64796e67, PC = 0x80144568 
21:32:390 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x64796e6b, PC = 0x80144570 
21:33:251 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x64796e67, PC = 0x80144580 

It also freezes upon selecting "Exit to main menu" and then loading the game again (though it does play, or at least start, the cutscene), with just this:

16:46:449 Core\PowerPC\PPCCache.cpp:192 I[PowerPC]: ICache read at 00dac280 returned stale data: CACHED: 4e800020 vs. RAM: 3d2080d7

This icache behavior is the same as with Scooby Doo! Mystery Mayhem (Bug 9561, a false positive where the existing icache check is returning stale data, when it probably shouldn't). I'll test.

EDIT: Tested, and the same hack that I found works with Scooby Doo! Mystery Mayhem works here (when combined with this change), namely changing this to return inmem. Both forms of exiting stop causing issues.

EDIT 2: Note that the ICache issue only comes up when MMU is disabled. When MMU is enabled, no changes beyond this PR seem to be needed.

[Rumi-Larry]

I get that the _US, is supposed to stand for microseconds (µs), but this is redundant, since it's already explained in the comment. Like it is, it can be confused for "United States", as if this latency is specific to US consoles. I recommend that part of the name to be omitted, reading MINIMUM_COMMAND_LATENCY

[JosJuice]

It's only redundant if you're looking at this specific line. The suffix is useful when you see the variable name referenced in the code, as it explains why we're dividing by 1000000.

[Rumi-Larry]

Got it!