sigma1

[Luke A. Guest]

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
persistence.

> 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
certain situations.

> 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.

Thanks,
Luke.