Re: [ECOS] processes vs threads (MMU protection)

[Thomas BINDER <Thomas dot Binder at frequentis dot com>]

Armando Visconti wrote:
> 
> Thomas.Binder@frequentis.com wrote:
> 
> > Hmm! I don't know the approach from 3GLabs, however, our process environment
> > (i.e. the classes that implement processes + the interface the user sees) is
> > *completely* architecture independent. All you need is a gcc2 or gcc3
> > compiler. The HAL needed to be changed to support the page table load
> > operation, that certainly *is* hardware dependent, but I guess that's what the
> > HAL is for. What needs further discussion is whether it is better to create a
> > new PPC HAL with MMU support, or to use compile time switches in the existing
> > one.
> 
> This looks fantastic to me. We have different products with different level
> of complexity. What I would like to do is being able to decide through
> configuration
> (and this is the key factor of eCos, right?) whether I want to include the MMU
> support or not!

Yes, absolutely. The process environment (and paging mode) is totally configurable. We also have boards where we currently don't use memory protection at all.

The memory protection comes in two stages, where the second (the process environment) depends on the first (the paging mode) to be turned on.

> > [...]
> > stack). Besides, our approach has been suggested in literature and was already
> > successfully implemented (I think there's a citation of Millers paper in my
> > original post).
> >
> 
> Where can I find some of the 'literature' you are reffering to?
> This is just my curiosity ...


You will find the citation plus some additional details in the announcement from April this year.

	http://sources.redhat.com/ml/ecos-discuss/2003-04/msg00311.html


> Is the documentation of how to port the HAL for supporting MMU already
> available? Yes, I know ... we can't do anything without the kernel support,
> but I'm curios to see what must be done to have such a support ...

No, we don't have a HOWTO that describes the necessary tasks. However, most of the functions you will have to implement are map/or unmap functions. You will find those in a file called hal_process_misc.c.

If you are really going to implement the MMU for another HAL I certainly can give you more detailed hints.


best regards,
Tom
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