bug in l2cr status display?

Adrian Cox apc at agelectronics.co.uk
Fri Aug 27 18:24:19 EST 1999

Michel Lanners wrote:
> It seems that the effect of the L2CR[DO] bit isn't clear. In the 750
> user manual, in the table describing l2cr, it says '... setting  this
> bit enables the caching of instructions'. This doesn't corrsspond to
> the name of the register, nor to what I see with my G3 upgrade card: in
> normal operation, L2CR[DO] isn't set, but it makes no sense to disable
> instruction caching excpet for test purposes.
> So, what's happening? Is the user manual wrong? In that case, we should
> correct arch/ppc/kernel/ppc_htab.c accordingly.

I think I posted a patch for this a while ago, but I've sort of lost
track. Basically, somebody in Motorola's documentation department
couldn't tell one from zero. In normal use the bit should be clear.
Hopefully somebody with write access will get the correct form into CVS.

They also got the Branch Target Instruction Cache the wrong way round. I
just hope that all firmware developers for G3 machines noticed these

> Any Motorola engineer around? Others with better docs? FWIW, I checked
> the 750 errata already... nothing.

It's in the errata to the manual, not the errata to the chip.

- Adrian Cox, AG Electronics

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