PPC 601 and mftb/mftbu

Cameron Kaiser spectre at floodgap.com
Mon Apr 26 17:37:28 CDT 2010

> The nearest instruction on a 601 is mfspr rd,6 which loads the
> decrementer. This is a user-level instruction on the 601 (not on the 603
> or later). So, -DEC roughly the tb.

I'd sort of independently determined this, although I settled on mfrtcu
which is spr4-5, IIRC. I'm not sure if it's high enough resolution for this
task, but as you point out, rdtsc() in the PPC nanojit is a function, so
it may not be a significant problem. mfrtcu/mfrtcl *should* work on the 603
and up, right?

However, the bigger problem is that the code generator is essentially
wedded to gcc inline assembly syntax, so I'd need to redo the whole thing
anyway to work for CodeWarrior and I don't fully understand it yet to do

Still, I'd like to resolve this for the future when I get enough gumption
to try.

------------------------------------ personal: http://www.cameronkaiser.com/ --
  Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser at floodgap.com
-- All the sensitive [men] get eaten. -- "Ice Age" ----------------------------

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