Run-ahead issues with 32X

[bslenul]

While reproducing this issue: https://www.reddit.com/r/RetroArch/comments/ni4vwo/picodrive_32x_and_runahead/ I noticed multiple issue with run-ahead and 32X games:

• Without second instance, run-ahead is disabled as soon as the content is loaded ("Failed to save state. Run-ahead has been disabled.").
• With second instance, run-ahead is disabled only after pressing a button ("Failed to save state. Run-ahead has been disabled." too).
• Still with second instance, weird stuff starts happening once you close content:
  • Run-ahead will be disabled for other cores that support it with a "Failed to load state. Run-ahead has been disabled." message (similar to Run-ahead isn't "re-enabled" on close content mupen64plus-libretro-nx#340 and Run-ahead isn't "re-enabled" on close content parallel-n64#728).
  • It'll mess up non-32X games loaded by PicoDrive, either by displaying a still image of the previous 32X game or by "refreshing" the screen only when you press a button :p

Video to show the issue in action (with second instance), and step-by-step of what I'm doing and what's going on in it:

2021-05-22.12-06-53.mp4

• I load Chaotix and press a button to trigger the run-ahead disabled message.
• I close content and start Castlevania Bloodlines and you can see it mostly shows a still image from Chaotix (and the resolution seems to switch a lot also).
• I close content and start the game again, it runs fine this time.
• I re-trigger the issue by booting Chaotix and pressing a button again.
• This time Catlevania Bloodlines display is "refreshed" each time I'm pressing a button.
• I re-trigger the issue one last time.
• I start Super Mario Bros. with Mesen core and you can see the "Failed to load state. Run-ahead has been disabled." message, even if it is supported by the core.

So yeah, super weird 😅 Is it even normal that run-ahead is disabled for 32X?

[irixxxx]

I have done some work on save/load stuff which is also used by run-ahead. Could you try this again please, with a core having at least revision 688c90d?

[bslenul]

Tested briefly, looks like it's still glitchy using 688c90d. It still disables on its own when pressing a button, then there are the weird issues after closing content and starting again, etc.

[irixxxx]

Is this happening too when saving?

[bslenul]

Pressing F2 to save state doesn't disable run-ahead, however Quick Menu > Save State disables it 🤔 Loading a state disables it, no matter if you use F4 or the Quick Menu.

[irixxxx]

Hmm. Which platform? Is this only with 32X games? How about MCD, MD, SMS, GG?

[bslenul]

Windows 10 64bit, I could try to reproduce on a Linux VM and Android a bit later.

Run-ahead + states work fine with MD, SMS and GG AFAICT, with MCD it seems broken after the BIOS however, graphical glitches in Night Trap for example:

with this kind of stuff in logs:

[libretro INFO] 00855:261: idle: don't know how to restore 4e75
[libretro INFO] 00855:261: idle: don't know how to restore 0026
[libretro INFO] 00855:261: idle: don't know how to restore 08d0

Sonic CD freezes multiple times on its main menu, once in-game it is playable but a bit slow, states work.

[irixxxx]

I think this is due to the fact that save states can't grow over time in retroarch, which is what's happening with 32x, where save states get bigger after 32x is released from reset by the 68000. Try enabling runahead after the image ran up to the sega logo.

[bslenul]

Oooh, yeah if I load Chaotix and enable run-ahead only after loading a level it works fine then!

[irixxxx]

There's no always-working easy test for a rom to check if it's using 32X or not. There's a field in the header which should carry this information, but it's presumably not always correct since it's not checked by the system (e.g. the original Sega SDK sample programs don't have it ;-)).
OTOH libretro wants to know about the maximum state save file size for a certain rom in adavance (i.e. on the 1st use of save/load). That would only be securely possible by including the possible use of 32X in the max calculation, increasing the memory needed for each state buffer by roughly 400KB. That doesn't sound much, but may lead to features like run-ahead not working on platform with very low memory.

[bslenul]

OK, thanks for the replies and explanation! Seems tricky to handle indeed... :/

I don't use run-ahead anymore so not affected by this issue anymore but I'm always up for testing stuff, so if you ever come with an idea don't hesitate to ping me (here or on Discord) if you need a tester.

Or I can just close the issue if you don't think it'll be possible to fix on the core side.

[irixxxx]

I'm going to change the max calculation to always include the 32X stuff for MD/MCD. I guess the memory would only be relevant to something like the PS2 (if it offers run-ahead at all). Less ancient systems should probably have enough memory to handle this.

[irixxxx]

I changed something in my repo to cover this, fixing 2 other bugs on the way. It should improve on both MCD and 32X run-ahead. Could you please check this?

[bslenul]

Run-ahead isn't disabled as soon as you press a button anymore, so progress! :D

There are still some weird issues however in 32X and MCD (32X or not) with the image being frozen sometimes until you press or release a button:

• In Chaotix when loading a level the screen stays black until I press a button.
• In Night Trap pressing Start to skip the intro results in either a glitched screen (like my screen above) or a black screen, until I press a button (tested both 32X and non-32X versions).
• In Sonic CD the image freezes every time I hit a Past/Future sign until I release the forward button or whatever button I'm holding on. It also has the same issue as Chaotix where you get a black screen when starting a level until you press a button. It also freezes on a boss every time his foot hits the ground. In the FMV if you press a direction for example, the image becomes glitchy until you press a button again, and then glitches again a few seconds later, etc.

And here's a quick video showing a few issues I've encountered in Sonic CD:

picodrive_runahead.mp4

You can see the intro glitches, the black screen on loading level, the freeze when hitting a sign and during the boss. For every of these glitches I have to either press a button or release the button I was holding during the freeze.

That was with irixxxx@92f7a43

[irixxxx]

Ouf, I made an error merging from the dev branch to master. Could you please try this diff, please:
y.txt

[bslenul]

OK just tried, all these weird image freezes are still there unfortunately.

[irixxxx]

Is run-ahead configured as 2nd instance for this?

[bslenul]

Yup, 2nd instance ON and a single frame of run-ahead. Without 2nd instance Chaotix doesn't even boot, it stays on a black screen, MCD seems fine however.

[irixxxx]

Could you recheck with the latest from my repo please. I've tried to fix some save/load problems and improve timing accuracy some, for md, mcd and 32x a bit. If possible do so in both one and two instance modes.

[bslenul]

Seems good with 2nd instance now 👍 No more weird image freezes or glitchy FMVs, etc.

Without 2nd instance Chaotix now boots, but sometimes it can't load the level, Knuckles keeps spinning for ever in a completely black background:

32X_no_2nd_instance.mp4

And sometimes it loads just fine 🤷 Same with content restart, sometimes it works fine sometimes it just freezes. I wasn't able to reproduce these 2 issues with 2nd instance.

[irixxxx]

I had a small regression in that code which I fixed. Don't know if it is related though.

[bslenul]

Yeah I was able to trigger the bug after a few retries, so probably unrelated. Wish I knew how to reproduce consistently, seems completely random when it happens :/

[irixxxx]

Can't reproduce it under RA on x86 linux :-(

[bslenul]

It's happening on my Linux Mint VM too, but it's 64bit (idk if it matters):

[irixxxx]

What's your run-ahead config for this? What exactly have you done?

[bslenul]

In Settings > Latency:

• Max Swapchain: 3 (when using Vulkan)
• Hard GPU Sync: OFF (when using GL)
• Frame Delay: 0
• Automatic Frame Delay: OFF
• Audio Latency: 64
• Polling Behavior: Late
• Run-Ahead: ON
• Run-Ahead Frames: 1
• Second Instance: OFF (like I said before, I wasn't able to reproduce the bug with it ON)
• Hide Warnings: OFF

I don't do anything special in-game, just starting it, pressing Start a few times until it loads the 1st level then it's random, either it'll load properly or Knuckles will spin indefinitely on a black screen.

[irixxxx]

No luck with these settings, in a Ubuntu 20 64bit VM...

[bslenul]

Damn :/ Just tried on a fresh install of RA to make sure it's not a setting messing with this but nope, I was able to reproduce the bug after 5 or 6 tries.

[irixxxx]

Hmm. I'm doing this:

• building lr-picodrive off the latest from my repo
• retroarch -L picodrive-libretro.so knuckles.32x # using both EU and US version here
• activating fast forward mode by hitting the space key
• hitting the start button several times until the level loads

that has succeeded for at least 30 times.
Is this a problem of the rom version? what's your md5?

[bslenul]

MD5: 47B1095E68B053125CD2CD5B1AC4EB50 which matches No-Intro database. Only tested with the "(Japan, USA)" version.

I'm building the core from your repo by simply using make -f Makefile.libretro -j4, it shouldn't require anything more, right?

edit: Hm, looks like I can't reproduce the bug with the EU version 🤔

[irixxxx]

Your build is fine. I have 2 different md5sums for my 2 versions, though.

[bslenul]

No idea if this is a useful info or not but I just tried disabling dynarec from the core options and it seems to get rid of the issue, although it's always hard to tell for sure due to the random nature of the glitch, but I wasn't able to reproduce in ~50 tries.

[irixxxx]

The timing isn't identical with interpreter and drc. The interpreter maintains the cycle counter on an instruction base, while the drc is doing this on a block base (a block being instructions from an address jumped to and the next jump). The drc is usually overdrawing its cycle budget for some instructions, while the interpreter stops after the instruction where the cycle budget runs out.
This usually isn't a problem, but additionally the exact sh2 cycle counters at save state generation aren't stored, which introduces some inaccuracy on load since that drc overdraw is taken out. I changed this, but now the level is appearing much later than with run-ahead off. I guess this needs some more investigation.

[irixxxx]

I did more improvments on saving/loading states, which might help here. You might want to check it out.

[bslenul]

After some quick tests it seems to be fixed 👍 Just to be sure I'll do more tests later then close the issue if I can't reproduce anymore :)

[bslenul]

Sorry for the delay! So yeah I can't reproduce the Chaotix bug anymore with single instance, however I have another issue in Night Trap (the 32X version): cameras are replaced with a still image from the intro movie.

Here's a video (you can skip to 0:40):

NT32X_edit.mp4

I don't know if the poor performances are normal also, sound is terrible and video stutters but since it's running without second instance maybe it's normal?

[irixxxx]

Is this running OK without run-ahead?

[bslenul]

Yeah, without run-ahead or with run-ahead + second instance it runs perfectly fine, it performs great and the cameras work properly.