Armin Steinhoff wrote:
Determinism = capping max latencies.
Capping max latencies doesn't help without a good real-time, event
driven scheduler.
But it helps to classify real-time operatings systems as so called
hard or soft real-time operating systems.
IMHO ... there is a common understanding that a RTOS can be considered
as a hard-reatime OS if the
max latency is < 15us because it is able to server 80% (?) of all
hard real-time applications in the field.
At some stage this might have been a pretty good response time.
But HW improves by leaps and bounds, and what was considered "fast"
or "real-time" 25 years ago might be your average vanilla desktop
box speed of today.
So, you'd have to define _exactly_ what operation completes
in under 15us? Again, it's these kinds of ambiguities that make
this a very woollen and fuzzy way to talk about subjects and needs
which are usually very precise and critical.
If your OS can support sub-us response times for some required
operation, I expect you wnat to say that, rather than a generic
"hard RT".
All others are considered as soft real-time operating systems. From
this point of view is PREEMPT_RT Linux
a hard real-time OS ... if the hardware base is appropriate.
Right. Regardless of what you call it, I would want the user to
understand very clearly what the OS is capable of, and what it
is not. And whether that meets their application's needs or not.
BTW ... we use PREEMPT_RT Linux as a base for our commercial
solft-PLC called DACHSview: http://steinhoff-automation.com/Programming.htm
Very interesting! Thanks for sharing that...
thanks,
Nivedita
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