Re: [ECOS]: Is eCos Hard Real Time OS ??

[Fabian Scheler <fabian.scheler@gmail.com>]

Hi,

I somehow have the feeling, that you have a somehow strange opinion
about what you call "hard real time systems", so what is a hard real
time system?

Well, the general understanding of a hard real time systems is that is
has to fulfill some tasks which underlie hard timing constraints
called deadlines. These deadlines must be guaranteed under all
circumstances otherwise the whole system fails.

But these tasks (these tasks do not directly correspond to threads or
processes!) are part of the whole real time system, t.m. of an
application, an operating system just provides an infrastructure to
execute this application. Deadlines now have to be guaranteed within
the application, not within the operating system, as these deadlines
are application specific! How should an operating system guarantee the
deadline of such a task? You have to analyze the whole application and
make sure that every task completes in time by some kind of formal
technique (WCET, scheduling theory ...).

The most important property of an RTOS is determinism, so you can such
formal techniques and verify your system. OK, some operating systems
do not provide an infrastructure that is suitable for building real
time systems,of course (eg. Windows, Linux ...), but eCos does.

At least: they way you are describing your requirements seems like you
are going to build a time triggered real time system, maybe eCos is
not the best choice here. eCos is better for designing event triggered
systems.

Ciao, Fabian

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