[ELDK] e500mc target architecture

[Wolfgang Denk]

Dear Valentin,

In message <50D043AB.4040007 at keymile.com> you wrote:
> 
> > Do you have any specific test cases and/or benchmarks that demonstrate
> > this, and that are relevant to your application code?
> 
> We do not plan to use virtualisation. Hypervisor may be needed for some very
> specific tasks, but we do not plan to use it in the current design. I was more
> interested in the sync and messaging instructions, but I think it is the same as
> with the new vector-scalar FP instructions, it's not very probable that GCC will
> generate them.

At least not automatically.  It should be possible to implement
specific versions of for example the mem* and str* functions; like an
optimized version of memcpy() similar to what has been suggested here
[1]; but again, it remains to be seen if this has any measurable
impact for your typical use cases.

[1] http://thread.gmane.org/gmane.linux.ports.ppc.embedded/50798/focus=55244

> There is still one point I would like to discuss: what is your experience with
> the -mtune and -mcpu compiler options ? Do you think it makes sense to add them
> to our compiler flags ?

I would prefer to use such flags consistently for the whole build, i.
e. including the system libraries.  But then, in I would expect that
-mtune =can be switched easily on a per-file basis as well.  I'd
recommend not to do this for -mcpu, though.

> The main problem I could see with this approach is if there are some
> incompatibilities between some libraries that were built without the flags and
> the application that was built with. Have you already experienced such problems
> ? The -mtune option at least should here be no problem since it does not change
> the architecture type nor register usage according to the GCC documentation [1].

Agreed.

Best regards,

Wolfgang Denk

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