[En-Nut-Discussion] RTOS + Cooperative Multithreading

[Jean Pierre Gauthier]

 Good remark...

Real-time is in fact often a subjective term related to an application. 
1 microsecond kernel delay or 1 second, what is the difference in term of
concept?
An OS is not real-time when the worst-case (WC) kernel activity cannot be
calculated.
I think that Nut/OS WC delay can be calculated. (malloc could be the dark
point?). 
Nut/Os is not preemptive. It can be annoying, because you have to "relax the
ticket" in any task, especially in the loops.

But...  a preemptive kernel  leads to a ton of problems around "critical
sections". Very complex to debug. Keep this in mind.
Demonstrate predictability is complex too, at level application. Some
methods exists for this like RM (rate monotonic)  & EDF (early deadline
first) but there are very pessimistic (see
http://en.wikipedia.org/wiki/Rate-monotonic_scheduling,
http://en.wikipedia.org/wiki/Earliest_deadline_first_scheduling) and the
most time, a statistical approach is done... So you need a RTOS but your
application has no real time guaranty!!!  ;-)
(but ok... even in a statistical approach, a "best case" for a specific work
delay  can be useful even if nothing is hard guaranted).  

"Nut/OS tasks" can be easy mapped to Linux threads where Nut/Os acts as a
"Linux task". 
For my point of view, Nut/Os is like a "super-small-on-chip-Linux".
I only regret that the systems calls are not 100% compatible with Linux. 5%
lacks...

Best regards,
Jean Pierre

-----Message d'origine-----
De : en-nut-discussion-bounces at egnite.de
[mailto:en-nut-discussion-bounces at egnite.de] De la part de daniela_24 at gmx.de
Envoyé : lundi 11 décembre 2006 15:03
À : en-nut-discussion at egnite.de
Objet : [En-Nut-Discussion] RTOS + Cooperative Multithreading

Hi,
why is the NUT/OS and the NUT/NET called a RTOS, when f.e. an endloss loop
can't be woken-up be and waiting thread with a higher priority??

In this context I can't understand what Real Time OS is really meaning.

Lot's of thanks for your help!

Daniela
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