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RE: MPC8260 cache patch


The particular problem I was chasing down was related to the fact that the
virtual vector table is in the first 16K.  (Perhaps it could be moved for
the '8620 platform).  RedBoot initializes pointers in there that do not get
committed to main memory before the flash initialization routine invalidates
the cache.

The only other solutions I can think of (now that you mention the major
problem of doubling the flush time) are to not place any writable data in
the first 16K or to choose some other 16K region of cacheable memory that
could be used to flush the cache.

--wpd


> -----Original Message-----
> From: Gary Thomas [mailto:gary at mlbassoc dot com]
> Sent: Monday, March 24, 2003 3:09 PM
> To: Patrick Doyle
> Cc: eCos patches
> Subject: Re: MPC8260 cache patch
>
>
> On Mon, 2003-03-24 at 13:00, Patrick Doyle wrote:
> > This one is probably for you, Gary.
> >
> > I ran into a problem wherein the data cache was not being
> properly synced
> > prior to being invalidated (somewhere in one of the FLASH routines --
> > 'flash_dev_query()', to be a little more precise).  I tracked
> it down to the
> > fact that the 'HAL_DCACHE_SYNC()' macro syncs the cache to
> memory by loading
> > in the first 16 kBytes.  But, if there are dirty cache lines in
> those first
> > 16 kBytes, they do not get written back out to main memory.  My
> simple fix
> > is to double the region scanned from 16 kBytes to 32 kBytes.  I would be
> > glad to accept an alternative solution.
> >
>
> I understand what you're trying to do here.  I recall a similar
> discussion on the Linux/PPC lists a few days ago, so I'm going to
> review that before we make this change.
>
> One question - what do you have in the low 16K that would be in the
> cache and how is it disturbing your FLASH routines?
>
> I ask because I am loathe to just double the cost of doing a flush
> unless it's 100% necessary.
>
> Thanks.
>
> --
> ------------------------------------------------------------
> Gary Thomas                 |
> MLB Associates              |  Consulting for the
> +1 (970) 229-1963           |    Embedded world
> http://www.mlbassoc.com/    |
> email: <gary at mlbassoc dot com>  |
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> ------------------------------------------------------------
>


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