More Performance (Using the MMU) ?

[BenoitAdam]

Hi,

I'm Xale00/BenoitAdam, and I'm actually trying my best to improve the port NullDC for Wii, which is a Dreamcast Emulator for Wii

The project has been very active since January :

https://github.com/BenoitAdam/nullDC4Wii

I'm working with legendary original NullDC develloper SKMP (who also did the GTA3 port to Dreamcast)

Actually games runs at worse on 50/60% of speed. Some games around 110/120%

Right now, we are starting to struggle on performance.

I was wondering if you have any tip or things recently implemented in devkitpro/devkitppc that could help us ?

Also, SKMP suggest using the MMU but he also says "libogc doesn't really like us doing that from what i gather"

What's your take on this ?

Thank you in advance !

[fincs]

What is the issue exactly?

Also, SKMP suggest using the MMU but he also says "libogc doesn't really like us doing that from what i gather"

In principle there shouldn't be any issues driving the PowerPC MMU from a libogc program. libogc only makes use of BATs, and considers the other address translation machinery (SRs/SDR1) to be up to the application to make use of. You can install your own custom DSI/ISI handlers (written in asm) using PPCSetExcptHandler. Note that exceptions that occur while handling other exceptions (i.e. RI=0) will always result in a panic. And also, make sure to translate buffer addresses to the appropriate 0x8.../0xC... addresses before using them with library functions (file IO, GPU, etc).

[BenoitAdam]

Thanks for your response !

not really an issue, more of a discussion. I tried to post on the forum 10 days ago but I think the topic never got approved

Here is SKMP's take on your answer :

skmp
yeah dunno
we need 512 megs of address space
tell them that
and that we need paging
but yeah it is doable
just a pain
building page tables by hand isnt fun

Xale (me)
Our friend Claude can probably help

skmp
yeah dunno, it is usually not so good about such low level stuff
maybe fable is beter who knows
The entire 0x0000_0000–0x7FFF_FFFF range is untranslated and free for you to claim
yea claude says we have the space
it can be done, just a pain in the ass

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If you have any additional information and/or example we are all ears !

[BenoitAdam]

thanks @fincs , we finally speed up the emulator thanks to your help : +15% measured !

What do you think about that, is that possible ?

L1 / L2 Cache Alignment: Ensuring hot JIT execution loops and data structures fit neatly into the Wii Broadway’s 32 KB L1 and 256 KB L2 caches.