The unofficial pcsx2 beta discussion thread

[hockland]

Pwned

[ahmedp23]

Pwned

ouch!!!

[Squall-Leonhart]

Hey, keep on topic you lot, if your going to only post something like pwned, or ouch,

unless you are going to include anything ontopic in the post, don't post at all.

There, now you both got pwned.

Now, what was the current direction of the topic?

[echosierra]

Last relevant post was about the ps2's non-standard fpu.

Are the fpu differences just a matter of bit width? I know the ps2's fpu does some funky clamping for values that cause overflow/underflow, but it seems kinda strange that some games (Metal Gear) would be so sensitive to the inaccuracies that gameplay would be impacted.

Is there publicly available documentation on the specifics of the ps2's fpu?
Finally, something in the emulator that I understand

[ahmedp23]

Originally Posted by Squall-Leonhart

Hey, keep on topic you lot, if your going to only post something like pwned, or ouch,

unless you are going to include anything ontopic in the post, don't post at all.

There, now you both got pwned.

Now, what was the current direction of the topic?

Sorry About That...the topic was about the minor grapic about front mission 4 in the wanzer setup.. im using pcsx2 0.9.5 svn 343

[Squall-Leonhart]

Originally Posted by echosierra

Last relevant post was about the ps2's non-standard fpu.

Are the fpu differences just a matter of bit width? I know the ps2's fpu does some funky clamping for values that cause overflow/underflow, but it seems kinda strange that some games (Metal Gear) would be so sensitive to the inaccuracies that gameplay would be impacted.

Is there publicly available documentation on the specifics of the ps2's fpu?
Finally, something in the emulator that I understand

you would be surprised just how sensitive any emulated game can be.

Take epsxe 1.6 for example, a couple lines of code wrong in the core, and FF9/Chrono Cross barely run on it for most people.

as for the FPU, being a floating point, the bit width would be required to change at key points,.. possibly for each bit of random data, and it can be very difficult to emulate a floating point in software.

I don't know jack about the PS2, but i did learn enough about floating points, vector units and fixed precision to know that im glad its Refraction doing this and not me.

[refraction]

Originally Posted by echosierra

Last relevant post was about the ps2's non-standard fpu.

Are the fpu differences just a matter of bit width? I know the ps2's fpu does some funky clamping for values that cause overflow/underflow, but it seems kinda strange that some games (Metal Gear) would be so sensitive to the inaccuracies that gameplay would be impacted.

Is there publicly available documentation on the specifics of the ps2's fpu?
Finally, something in the emulator that I understand

not sure if theres anything publicly available, but youd be right. the PS2's FPU (more specifically the vector units) have strange value rounding, they dont support positive or negative infinities, nor do they allow NaN values.

doing this on a chip which does account for positive/negative infinities, controls NaN's and has multiple rounding modes, its quite difficult! ;p

[Phil]

well the higher the detail in game (MGS3), the more dependent the game becomes on the balance of those values, wierd as they may be. thats why FFX is relatively easier to emulate imo.

[refraction]

Originally Posted by Phil

well the higher the detail in game (MGS3), the more dependent the game becomes on the balance of those values, wierd as they may be. thats why FFX is relatively easier to emulate imo.

well yes and no. the problem is, some developers exploit these restrictions on the system to do what they want to do, which causes us problems. fortunately apart from the small hack needed for FFX (a method they exploit to flush the VU's) it is all pretty much making good use within the specs of the system. where MGS3 uses alsorts of FPU exploits, VU stalling to sync data and other nonsense.

Again KH2 is another example. Im sure most of you remember it being a spikey mess, that was due to Square (again) exploiting the delays of the vector units to do calculations then do another calculation using the old values before the results of the previous calculation come back. Its horrid, but its something we have to live with.

[cottonvibes]

Originally Posted by refraction

Again KH2 is another example. Im sure most of you remember it being a spikey mess, that was due to Square (again) exploiting the delays of the vector units to do calculations then do another calculation using the old values before the results of the previous calculation come back. Its horrid, but its something we have to live with.

wow, that does sound horrid.
i didn't know the game devs would do something that tricky :O
i'm suprised you guys were able to fix something like that.
great job

[Phil]

hmmm..well does this exploitation make the game easier for them to make?

[Squall-Leonhart]

Originally Posted by refraction

not sure if theres anything publicly available, but youd be right. the PS2's FPU (more specifically the vector units) have strange value rounding, they dont support positive or negative infinities, nor do they allow NaN values.

doing this on a chip which does account for positive/negative infinities, controls NaN's and has multiple rounding modes, its quite difficult! ;p

i think Sony released PS2 information and some docs on the FPU to the linux community...

[refraction]

Originally Posted by Squall-Leonhart

i think Sony released PS2 information and some docs on the FPU to the linux community...

yeh ive got docs on it with the responses to certain values. it doesnt make things much easier though.

[Squall-Leonhart]

looking at the chips internals wouldn't help would it?

[refraction]

Originally Posted by Squall-Leonhart

looking at the chips internals wouldn't help would it?

not really, the problem isnt lack of understanding, its the lack of simularities between the handling on x86 and the VU's architecture (MIPS too). We "could" account for this, but it would kill the speed of the emulator in doing so.

[Squall-Leonhart]

ok, i guess accurate and compatible PS2 emulation won't be complete till we have 10gh cpu's then :P

[guillee]

hi, congratitulations for the progress, what about use the new CUDA tecnology of nvidia?, its posible to implement it in some high latency parts of the emu? in a near future, of course. saludos

[refraction]

Originally Posted by guillee

hi, congratitulations for the progress, what about use the new CUDA tecnology of nvidia?, its posible to implement it in some high latency parts of the emu? in a near future, of course. saludos

its funny you should mention CUDA. the float unit on graphics cards (modern unified ones) is exactly that of the VU, strangely. I know i know, "why dont you put the VU's on the graphics card?" well, to name a few reasons.

1. It would mean the team would have to actually learn how CUDA works which means bye bye to any ATi users (which would be roughly 40-50%)
2. We would have to find a way to successfully implement it without hindering compatability, whilst learning how CUDA works.
3. the GS emulation is causing enough strain on the GPU as it is without VU emulation bogging it down too!

so there you have my top 3 reasons why we dont take advantage of this situation

[Mkilbride2588]

Yikes refraction, this is madness. I can see why everyone else gave up on a PS2 emulator...honestly, I know very little about coding, but from what I do know, I looked at PCSX2's and kinda blanked out for a few minutes and closed it.

I really wish OTHER teams were making PS2 emulators, just cause like, if there was, if one team made a breakthrough, they could help the other team, and then in turn if THAT team had a breakthrough, they'd share it, and it'd really help ease the workload, I'd guess.(Of course, thinking emulator teams would co-operate like that is abit idealistic:P)

[refraction]

yeh, fortunately for me i joined late on, so i missed the hardest part but it isnt easy by all means.

the team and pSXAuthor have been helping each other out time to time, as hes got industry experience in coding ps2's and we have ps2 emu coding experience, it kinda helps each other out, plus if theres any ps2 emu id like to see appear, it would be pSX