[Embedlets-developer] RE: [arch] Poor man's realtime

[Ted K. <tk...@ya...>]

Andrzej,

>> I think it is the real-time nature of Embedded programming that puts
>> people in a bit of a spin. 

>I've been thinking about this.  Creation of a container 
>implementation that can support real-time (in the strict, 
>embedded sense of the word) is a very difficult 
>task.  My current thinking is that Embedlets won't be able
>to support pure real time (with the millisecond response 
>times and prioritizations this requires) in it's first few 
>incarnations, and that this would be too ambitious a goal for us 
>to try and tackle out of the gate.
>
>Thoughts?

The initial research that was done with the JAPL idea indicates that a poor
man's realtime capability could be made available to the Embedlet container by
adding something like a Determinism interface to the appropriate JAPL
peripherals that would allow their determinism capabilities to be queried and
configured.  For example, a PIC based muvium device that was implementing a
SquareWaveGenerator JAPL peripheral could indicate that it was capable of
producing square waves with periods as short as 1 microsecond.

The strategy for developing Embedlet based systems with realtime capabilities
would then be to move as much of the deterministic code as possible to the
implementation side of the JAPL peripherals and then implement it with whatever
technology works best.  As an example, if a speed controller Embedlet was
developed against a JAPL SquareWaveGenerator interface, at build or run time it
could query the deterministic capabilities of the specific JAPL instance that
implemented the interface in order to determine if it was capable of meeting
its temporal requirements.

If the peripheral indicates it is capable then everything should work OK.  If
it is not capable then the Embedlet could either reduce the level of service it
can provide or force the developer to implement the interface with a more
capable piece of hardware.

It is not quite RTSJ but it seems to be 'straight forward' and it might prove
to be good enough for a number of uses.

A side thought here is that a JAPL interface which also had temporal
requirements attached to it would be an interesting way for a company
developing an Embedlet based embedded system to post their JAPL peripheral
needs on the net and then let third party developers compete for the contracts
to implement them.


Ted


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