[coreboot] Cache as RAM - is it possible to execute code in cache?

Jackie Pan jackiepan93 at gmail.com
Sat Sep 6 01:08:35 CEST 2008

2008/9/5 Stefan Reinauer <stepan at coresystems.de>

> Carl-Daniel Hailfinger wrote:
> > On 05.09.2008 12:54, Stefan Reinauer wrote:
> >
> >
> >> On 05.09.2008 09:45, Jackie Pan wrote:
> >>
> >>> if it's possible to place code into cache-emulated RAM
> >>>
> >> Core 2 Duo can do cache for ram and code... But it works well enough
> >> to just set an mtrr to make rom cacheable during car and that also
> >> works for older intel CPUs
> >>
> >
> > We're talking about different things.
> > Jackie was talking about executing code stored inside the pseudo-RAM CAR
> > area. I was talking about that as well.
> > Stefan wrote about using cache for code outside the CAR area.
> >
> No, not at all different things. As I said, the Core 2 Duo can execute
> code stored in CAR.
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> Hi Stefan,
I'm very curious about how you achieve this. As Intel's separate L1 data
cache and instruction cache,after checking the prog. manual I come to the
conclusion that the i-cache can only be filled by instruction fetching
process(or am i wrong?), when I copy code into the CAR region(i.e., not by
caching of the XIP region using MTRR),
the data I supplied goes directly into the d-cache, at the same time the
corresponding line in the i-cache(if any) gets
invalidated immediately, or more exactly for the CAR case, there's no such
line in the i-cache at all because there's
not been any instruction fetching targeting at the CAR region before. Thus
it seems impossible to synchronize the
i-cache and d-cache without a RAM as backup.

let me guess, are you implying storing  to another core's cache while using
MESI for the purpose of synchronizing?
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