Re: [Xenomai-help] my tick takes a break !!

[Philippe Gerum <rpm@xenomai.org>]

Gilles Chanteperdrix wrote:
> Philippe Gerum wrote:
>  > Gilles Chanteperdrix wrote:
>  > > Philippe Gerum wrote:
>  > >  > If you feel lucky, the 3rd option coming with v2.2 is to get rid of the 
>  > >  > UVM and use the new direct call interface now available from user-space 
>  > >  > for the VxWorks skin. In such a case, you need 1) the development 
>  > >  > trunk/, 2) to load xeno_vxworks, 3) work with the new VxWorks interface 
>  > >  > from user-space exactely the way one would use the existing native or 
>  > >  > POSIX skin.
>  > > 
>  > > But round-robin scheduling will not work for threads in secondary mode,
>  > > whereas it works with UVM.
>  > > 
>  > 
>  > Sorry, I don't get the point. If it works in secondary mode under the 
>  > UVM, it will work outside the UVM too, since we have shadow threads 
>  > scheduled by Linux, in any case.
> 
> A thread in secondary mode in Xenomai kernel-space nucleus, is seen as
> the root thread, which never has the XNRRB bit set.
> 
> The UVM nucleus, on the other hand, has no notion of primary or
> secondary mode, when a thread is running in secondary mode it still is
> the current thread, so may have the XNRRB bit set.
> 

Indeed, but as a user, you must _not_ rely on this internal knowledge of 
such "UVM over shadow mapping", never, ever. The UVM must been seen as 
having the very same semantics than direct call interfaces, except that 
almost every nucleus action is occuring/confined within a single process 
context when possible, hence the virtual machine thingy. The fact you 
describe is a hidden side-effect which must never be taken for granted, 
otherwise, transitioning from the UVM to direct call interfaces is going 
to be extremely painful...

-- 

Philippe.