Enable of Data Cache on mpc8240 and mpc8245

Till Straumann strauman at slac.stanford.edu
Wed Feb 22 22:54:11 UTC 2006

Jennifer Averett wrote:

>I don't know if anyone has already resolved this,
I had. (my message from 2005/11/18 attached).
I committed everything *but* the actual L1_caches_enables() call
(I got delayed and now I don't have the loaner 2100 board anymore).
However, I am sure I tested it and it worked. But since I cannot test,
I was reluctant to commit this.

> but I was able to enable
>data cache on an mpc8245 processor.  I had to move the L1_caches_enables
>call to the bottom of the pretasking hook.
why would you have to do that? For me, it worked the 'normal' way:

start.S: cache off, MMU off
            setup bat to map memory
            (should set up basic/empty page table but that is currently 
not done)
            MMU on

            setup MMU/bat mappings for I/O *prior* to doing *any* I/O
            enable L1 cache

Two states that must be avoided:
   MMU off, cache on   [all operations would be write-back cached,  
including  I/O
                                     which is bad]

   MMU on, insufficient mappings [ I/O fails w/o a way to print to console]

HTH Till


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