Operating System design is my concentration in school right now so I understand the basic principles of Virtual Memory and the Translation Lookaside Buffer. But, while my OS design concepts are up to snuff, my knowledge of emulation algorithms is very subpar. So here's my question: What exactly is VTLB and, when the implementation is finished, how will it affect the PS2 emulation scene?
What is VTLB?
01-20-2009, 10:19 PM
If anyone can enlighten us, I would also like to know exactly what VTLB is.
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What i do know is that it will be the future of the emulator and VM was used for a while and it was a big hack but right now its hard to keep working and keeps having problems. The developers do not want to give up totally on VM.
01-21-2009, 12:04 AM
theres a post about this zerofrog made along time ago:
in short, VM basically uses some hacky workarounds to not have to use a TLB, by relying on "EXCEPTION_ACCESS_VIOLATION exceptions to remap the correct physical page to that empty virtual page".
that was enlightening ^^ Thank you very much ~
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01-21-2009, 05:50 AM
If I got that article right they tap into exception handling ( or signaling for those knowing hacking ). Doesn't seem to fully work though as some games manage to crash the emulator. Nasty situation to get working properly. So PS2 has a 4GB Virtual Memory? How much actual memory does it have?
01-21-2009, 06:39 AM
VTLB works by properly emulating the TLB portion of the PS2, or at least as properly as is allowed by Pcsx2's exception handler (which itself is only about 30% emulated). Previous versions of Pcsx2 did not emulate the PS2's TLB at all. The old TLB build was named so after then Windows/x86 translation look-aside buffer, and not for the PS2's. The VM build, in turn, ignores even more aspects of PS2 memory emulation than the old TLB did.
VTLB, like VM, also uses virtual memory protection (the EXCEPTION_ACCESS_VIOLATION stuff) to speed up emulation -- but it does so in a much more efficient manner than VM. Ultimately, VTLB should be able to emulate the PS2's memory a bit more quickly than VM does, but the state of the Pcsx2 recompilers make it difficult to do at this time.
Jake Stine (Air) - Programmer - PCSX2 Dev Team
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