Luke A. Guest
laguest at archangeli.demon.co.uk
Wed May 24 14:28:13 CEST 2006
On Wed, 2006-05-24 at 11:56 +0000, Jeremy O\'Donoghue wrote:
> Luke A. Guest <laguest <at> archangeli.demon.co.uk> writes:
> > Hi,
> > I've just started to look at L4 and I'm using L4ka::Pistachio as a
> > starting point. I'm trying to read as much as possible and have found a
> > reference to sigma1, but no docs on it. Can anyone elaborate on what
> > this is for?
> AFAIK, sigma1 disappeared a long time back - I've been working with Pistachio
> for about 18 months now, and have never seen it!
I just wanted to know what it was as I'd seen it mentioned, but nothing
else was documented, then I saw references to it in relation to
> Given the name, I suspect that it probably formed part of a previous
> implementation of platform memory management. On more recent Pistachio kernels,
AFAIK, sigma1 is not implemented in the Pistachio kernel, although there is persistence
work going on on l4ka.org.
> a privileged thread, sigma0 'owns', all platform memory on startup. Thread
> pagers (root task, by default) obtain memory by requesting it from sigma0.
> Sigma0 has disappeared from the latest Pistachio kernels as well, so even the
> information above is version dependent.
Really? I've not seen this, which version? I'm using 0.4 Pistachio from
the downloads area.
> Learning about L4 in general can be frustrating as, being in significant part, a
> research vehicle, much of the background documentation is in conference papers
> and thesis extracts, and dates quickly (L4::Pistachio is evolving very rapidly).
> The background material is still useful, but you need to be aware that it's not
> always relevant to the latest releases.
Tell me about it, I'm also relearning the OS theory as I go along at the
same time. I'm totally confused by memory handling at the moment.
> The source code is your friend here (although the user manual and refman are
> reasonably up to date). Most of the code is well written and structured (if
> sparsely commented), although it requires very good C++ and CPU platform
> knowledge to follow in detail.
Yeah, I'm trying to find as much as possible to see what others do in
> You don't mention whether you have done so or not, but you would be well advised
> to start off with the Iguana release. Iguana presents a much more friendly API
> on L4, and is also a very useful source of programming techniques.
I have got the Iguana source code down, but it's difficult to find
something specific when you don't really know it very well.
I'm attempting to document my efforts here:
http://www.geocities.com/munkee_chuff/ Feel free to read it and email me
with anything I might get wrong.
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