[aadl]: Cyclic Immediate Connections in AADL

[Andrew Gacek]

I have a related question about connections and scheduling. In the
attached picture I have two threads A and B with an immediate
connection from A to B. I also have a input data port on the
surrounding process with a connection to both A and B. Assuming that A
and B run at the same rate, under what conditions can we assume that
they see the same value on that incoming port?

-Andrew

On Thu, Dec 18, 2014 at 4:27 PM, Peter Feiler <phf at sei.cmu.edu> wrote:
> This consistency rule is still true independent of whether we have
> partitions or not.
>
> Partitions just introduce additional cyclic dependency rules that affect
> units that do not talk to each other – see my two thread pairs example.
>
>
>
> Synchronization domains has to do with different clocks. We do not have
> anything in the standard as to whether immediate connections are supportable
> across such domains or under what assumptions (e.g., on top of PALS).
>
>
>
> Peter
>
>
>
> From: Jérôme Hugues [mailto:Jerome.HUGUES at isae.fr]
> Sent: Thursday, December 18, 2014 3:47 PM
> To: Peter Feiler
> Cc: Andrew Gacek; Julien Delange; sae-aadl-users at lists.sei.cmu.edu
> Subject: Re: [aadl]: Cyclic Immediate Connections in AADL
>
>
>
>
>
> Le 18 déc. 2014 à 15:32, Peter Feiler <phf at sei.cmu.edu> a écrit :
>
>
>
> Immediate connection cycles is an interesting issue. It exists for
> connections between periodically sampling units, e.g., two threads, two
> devices, or a thread and a device.
> The reason is that immediate says that one is to execute before the other in
> the same period and you cannot have both before the other.
> In other words, it is best to check in the instance model.
>
>
>
> I do agree with your interpretation Peter, but my standard says, in 9.2 (C1)
>
>
>
> (C1)  There cannot be cycles of immediate connections between threads,
> devices, and processors.
>
>
>
> So I’m lost .. did we overlook this one ?
>
>
>
> Although  the first part of section 9.2.5 discusses the case for
> periodically sampling units and immediate connections, I usually use
> immediate connections for what they are: they detail when the data is
> actually sent. So we definitely need to separate the two issues
>
>
>
> Cycles of periodically sampling units should be forbidden under the
> assumptions of the synchronous models of computations
>
> (e.g. these are forbidden in SCADE and Esterel, under the term causality
> loop). It is probably what should be clarified in terms of synchronization
> domain. Within one synchronization domain (e.g. one hyperperiod), they
> should not be allowed
>
>
>
> If there is no restriction in terms of synchronization domain, these can be
> allowed: we just mandate the instant of transmission, but the user is on its
> own in terms of data consistency.
>
>
>
> It gets more interesting. P1 and P2 are mapped into different ARINC653
> partitions and they execute on a static time line, then P1 has to be before
> P2 and P2 before P1, i.e., we have a cycle. However, this cycle can be
> broken by giving each partition multiple windows and allocating the threads
> such that P1.A -> P2.B/C -> P1.A in a major frame.
>
>
>
> So here you have implicitly (or not ?) a synchronization domain. I mean
> implicitly from the use of ARINC653 properties
>
>
>
> Regards,
>
>
>
> —
>
> Jerome HUGUES
>
> Enseignant-Chercheur -- Ingénierie des Systèmes Embarqués/Embedded Systems
> Engineering
>
>
>
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>
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>
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