PS one game compatibility

[Blyss Sarania]

I'd prefer solid USB peripheral/microphone emulation over PS1 emulation anytime.
Also for the record, PS2 does not have 100% compatibility with PS1 games, you'd be surprised to know that even a couple of very famous games don't work at all on PS2.

It has pretty good compatibility though. Some of the games that don't quite work right have config ***** on the memory cards too. That's how we can do the PS1 exploit for Ule

[VIRGIN KLM]

That's how we can do the PS1 exploit for Ule

Ummm, I'm pretty sure PS2 hacks were based on the CDVD Driver and Browser firmware update checks on the memory card.
They allowed for firmware updates via BIOS patches, effectively allowing circumvention of code execution blocking measures.
I really enjoy FMCB on PS2, I wish it was a thing and as famous when I was a kid though. This together with the extra homebrew just made PS2 an even better console of what it already was/is.

[Blyss Sarania]

Ummm, I'm pretty sure PS2 hacks were based on the CDVD Driver and Browser firmware update checks on the memory card.
They allowed for firmware updates via BIOS patches, effectively allowing circumvention of code execution blocking measures.
I really enjoy FMCB on PS2, I wish it was a thing and as famous when I was a kid though. This together with the extra homebrew just made PS2 an even better console of what it already was/is.

There are lots of different hacks. The one I am specifically speaking of is the PS2 Indepedence exploit.

As I said, PS2 memory cards contain a small file with various settings for PS1 backwards compatibility. The Indepedence exploit works by you replacing the file with a modded one using an Action Replay or the like. The modded file contains a specially crafted entry. During the process of setting up the exploit, you pick a PS1 game as a trigger disc. Then when you transfer the modded backwards compatibility file to the memory card it now contains a new entry for whatever PS1 game you chose. When you boot the PS2 with that PSX game in it, it triggers a buffer overflow and allows unsigned code to run.

That's how I originally modded my PS2, before Free McBoot was a thing.

[VIRGIN KLM]

There are lots of different hacks. The one I am specifically speaking of is the PS2 Indepedence exploit.

As I said, PS2 memory cards contain a small file with various settings for PS1 backwards compatibility. The Indepedence exploit works by you replacing the file with a modded one using an Action Replay or the like. The modded file contains a specially crafted entry. During the process of setting up the exploit, you pick a PS1 game as a trigger disc. Then when you transfer the modded backwards compatibility file to the memory card it now contains a new entry for whatever PS1 game you chose. When you boot the PS2 with that PSX game in it, it triggers a buffer overflow and allows unsigned code to run.

That's how I originally modded my PS2, before Free McBoot was a thing.

What happens with PS1 emulation if a MC is missing?

[Blyss Sarania]

What happens with PS1 emulation if a MC is missing?

It's only needed for some PS1 games, basically the ones that have issues with the "default" configuration. But for those games, if you have no PS2 memcard they will have issues/not work.

I'd link you a source but I'm having trouble finding them nowadays, seems to be lost to time. It used to be pretty well known, I believe there was even official Sony material that said backwards compatibility would suffer without a PS2 memory card, but yeah I can't find it nowadays.

I did find this, from information on the Independence exploit:

When a PlayStation (PS1) game is loaded in the PlayStation 2, the console looks for a file called TITLE.DB which, if present, is located in the Memory Card's directory BxDATA-SYSTEM (where x is a letter corresponding to the console's region –e.g.: E for the EU, A for the USA or I for Japan, this directory corresponds to the System Settings save). This file is a database of special options to be applied to specific PS1 games for their correct operation.

Also here is some more information on Independence:
https://books.google.com/books?id=h_yJNav8tuMC&pg=PA165&lpg=PA165&dq=ps2+independence+exploit+how+does+it+work&source=bl&ots=VoXpIN08Uy&sig=UraKlbRX0bxATGnCD9MFGMIQICM&hl=en&sa=X&ved=0ahUKEwj66rqGyr7JAhUKRiYKHU56AX4Q6AEIQTAG#v=onepage&q&f=false

Note it says in there that the exploit only works with Sony cards, and this backwards compatibility stuff is why.

[rama]

Regarding compatibility of PSX titles on a PS2:
The earlier console revisions had very good compatibility. That situation got worse though when Sony started to make drastic chip integration changes.
Later slim consoles that integrated the EE and IOP had a lot of new issues with PSX titles.

So yea, obviously we'd aim for early PS2 behaviour

It's not clear yet if we're missing anything in SIF2 mode. That part has been worked on but I don't know if it works.
Then we currently fail at the GPU or GTE (which should be software emulated on the PS2. No problems there.) initialization.
Either the "chips" don't reply correctly or the data channels are missing or wrong.
Someone with knowledge of how the PSX boots up would be able to tell us immediately.

[willkuer]

This would mean pcsx2 is bios dependent regarding psx emulation?

[PapermanZero]

But makes it sense to integrate PS1 Emulation to PCSX2?
I mean there are already very good PS1 emulators.

PCSX Reloaded for example provides very good support and is open source.
Sadly, the development seems to decrease, although there is a lot of potential.
So the motivation for this development must be increased again.

The most obstacle for a continuous development of PCSX is the plugin-system with the missing resources.
The common goal should be to create plugins which support both emulators PCSX (Reloaded) and PCSX2.
Lilypad is the best example. Using Lilypad for both emulators decreases efforts on both sides to maintain the plugin.
Currently Lilypad is working flawlessly with both emulators. The same approach could be used for graphics and maybe audio.

Most graphic plugins are closed source for PCSX and nobody can maintain them. If GSDX would be extended to support PCSX (Reloaded), another obstacle would be gone. The needed features for a modern graphics plugin would be:
- Open Source based on OpenGL
- High Resolution Rendering
- Texture Filtering (maybe with external shaders)
- Anti-Jitter or GTE accuracy
- Quad Polygon Rendering
- Possible z-Buffer with Anisotropic filtering.
- Texture Exchange Option
- Frame Limiter
- Widescreen

My personal feeling is, that also GTK+ is limiting the development of PCSX (Reloaded). Maybe it would be good to go for wxwidgets or Qt, which is much simpler to maintain for the different OSs.

So all in all it makes no real sense, to implement PSX emulation in PCSX2, if other emulators are more advanced and only need maintenance.

[willkuer]

If you would've read the thread you would know that providing another psx emulator is not the point. The psx emulator on the ps2 was far from perfect and with LLE we could only get something as good as on the ps2 concerning compatibility.

The point is to improve the ps2 compatibility. If pcsx2 would be a perfect ps2 emulator all features of the ps2 should work perfectly. Obviously we can not emulate psx games even if the ps2 is able to do it. This leads to the conclusion that pcsx2 is not perfect. If we fix now psx compatibility it is possible that we fix all other issues (with the core) as well. Psx compatibility is a benchmark for ps2 emulation accuracy and not a feature to play psx games.

[PapermanZero]

Indeed. I started only the first pages.
But why not selecting some benchmark games?
The question is always what do you want to benchmark?

As already mentioned the PS2 had different degrees of compatibility with PS1.
Reason is the changed hardware. Btw same for PS3 and PS2. So you are going to benchmark against the hardware which was dedicated for PS1 compatibility, which has eventually no relevance for PS2 games at all.
So to use PS1 compatibility as a benchmark is risky and maybe not relevant.

If the PS2 hardware would emulate PS1 hardware, I would agree that you could benchmark (like the Wii did with the virtual console).
But due to the special tailored hardware within the PS2 for PS1 games, it's maybe not a good approach.