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    SubjectRe: RT patch acceptance
    >>>>> "Esben" == Esben Nielsen <> writes:

    Esben> On Tue, 31 May 2005, James Bruce wrote:
    >> It is only better in that if you need provable hard-RT *right now*,
    >> then you have to use a nanokernel.

    Esben> What do you mean by "provable"? Security critical? Forget about
    Esben> nanokernels then. The WHOLE system has to be validated.

    The whole point of a nanokernel is it's *small*. The whole thing can
    be formally verified. And its semantics will provide isolation
    between the real-time processes and anything else that's running.

    We're currently working on a system called Iguana, which will have
    provable WCET for real-time scheduled tasks, and a Linux envionrment
    (called `wombat') that provides compatibility for

    Esben> I can't see it would be easier prove that a nano-kernel with
    Esben> various needed mutex and queuing mechanism works correct than
    Esben> it is to prove that the Linux scheduler with mutex and queueing
    Esben> mechanisms works correctly.

    Except that the nano-kernel is less than one percent of the size.

    Both systems does the same thing
    Esben> and is most likely based on the same principles! If a module
    Esben> in Linux disables interrupts for a non-deterministic amount of
    Esben> time, it destroys the RT in both scenarious. With the
    Esben> nanokernel, the Linux kernel is patched not to disable
    Esben> interrupts, but if someone didn't use the official
    Esben> local_irq_disable() macro the patch didn't work anyway... The
    Esben> only way you can be absolutely sure Linux doesn't hurt RT is to
    Esben> run it in a full blown virtuel machine where it doesn't have
    Esben> access to disable interrupts and otherwise interfere with the
    Esben> nano-kernel.

    This is precisely the approach we (and others) are taking. A
    virtualised Linux to provide interactive and soft realtime (think java
    games on your mobile phone), and a nanokernel for your hard realtime
    tasks (think the radio controller on your mobile phone).
    See for our work.

    In addition to our work, there's the Adeos system
    ( uses a very similar approach.

    Dr Peter Chubb peterc AT
    The technical we do immediately, the political takes *forever*
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