Re: [gentoo-embedded] Hard Real Time Systems with Gentoo?

[wireless]

Bob Paddock wrote:
> Does anyone know of any Hard Real Time Systems,
> where deterministic response is required, that work
> with Gentoo-Embedded?


Um, the way you posed your question, is sure to solicit
'religious wars' on a few issues.

Soft real time, means that timing constraints are soft
or guildlines for process performance metrics.

Hard real time, means the timing constraints are hard
or an absolute requirement. Granted, most often these
timing constraints are arbitrarily set, but a system that
violates those arbitrary timing constraints is said
to not be 'real time'. But think about if a missile,
is suppose to change it's rudder in response to an
AD input, in 150ns, does it mean that the missile   as
as system is a failure if the rudder response is
151 ns or 150.002 ns?   Usually not the case, in fact
rarely. The designer settle for the best (lowest latency)
response in a particular subsystem that they can get.

Determinism is another funny character. Real embedded
systems use a 'state machine' design where every
state or transition is fully characterized and defined.

ON a large complex system, it is virtually impossible to
discover, characterize, define and test all possible states
of a complex system. (just look at the behavior of a single
female of any given species). Biological systems are but
one example of a system that cannot be fully characterized
due to many factors but genetic modification being one
example.

A microcontroller that is part of a complex system, can
have hard (RT) timing constraints, and be implemented in
ansi C or assembler on a state machine. Traditionally, that's
been done for years. It's mostly too expensive to do currently,
so intelligent people have 'diluted' the methodologies
so that other altruisms are commonly promoted, in the
name of science.

Embedded linux anything, currently, can never be fully deterministic.
Using languages such as C++ or more reaching OO languages, only
exasperates the goal of being fully deterministic. In stead of
the educators realizing and admitting that very few things
actually need HRT and virtually nothing complex that we build,
mimic or model is actually (fully) deterministic, pop-science
and pop-mathematics has infected what is traditionally a common
sense based standard of acceptable science.

That said, you can 'embedded gentoo/linux' onto a processor;
and this a most wonderful thing to do,
and not allow a user to access the cli but only use the
fancy touchscreen, as a consumer or operator, and have performance
that is embedded and appears 'real time' to the human senses.
You cannot actually build a deterministic system using
any form of embedded linux or any OO language.


<flames on>  Obviously, you'll find lots of vendors and educated
folks that will disagree, and they have, and the debate continues.
As part of a company that has been building products for companies
for decades, most new products do not even have a specification,
as it evolves based on what the firmware engineers can accomplish
on the newest silicon provided my semiconductor manufactures.

Only the DOD, Nasa and such even attempt to define an embedded
subsystem that is actually HRT, let alone fully deterministic.
These are fancy monikers promoted by marketing types, MBA
and sales professionals.

There are lots of white papers around the net on FSM (finite
state machines) and determinism. Maybe some tiny portion of what
you seek to build needs HRT or determinism? Isolate that, and
settle for best/reliable performance in an embedded linux/gentoo
processor.

Here's but one reference of the many confused reference you'll find:
http://fsmgenerator.sourceforge.net/
If you really want determinism, stay with native assembler and
ansi C.

enjoy!

<ps, keep the flames focused a technical discussion/opinion>

James









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