RMA Analysis

[peter.o.mueller at gmx.de]

Hi,

starting to analyze our system with RMA glasses brings up several question
;-) As background I red the rtems-manual and also the book "Meeting deadline
in Hard-RT Systems" form Briand/Roy. Now I have some questions related to what
rtems offers or better what do I need to know about rtems.

Reading the book I learned that for tasks not sharing ressources (no
blocking) basic rma analysis as described in the rtems manual is sufficient. But for
tasks sharing ressources blocking may occure and therefore max. blocking
times should be included in the rma analysis. This requires that the OS is able
to rise the priority of tasks owning
the shared ressource dynamically to limit blocking times.

Some background info:
- Our system architecture is that of a shared datastore. There is a set of
data available and objects needs to read and write that data.
- As described in the rtems manual our system consists of one critical task
(a) which, after initialization, performs several sets of actions cyclically
(e.g. every 100 ms)
- An aktion (=object)  with longer run-time, runs its own task (b) with
typically lower priority than task (a). E.g. task dealing with slow hardware 
- Obviously it is necessary to lock access to the shared datastore. 

This brings me back to blocking:
- Does rtems support dynamically rising the priority that seems to be
necessary to limit blocking time. If not, how to deal with that?
- what is the best way to model task (a) utilizing the rma approach. As I
understand it each action is a task in rma with cycle time, execution time ... 
- Are there papers available describing the approach to put the critical
actions in one task? I found nothing about that in the mentioned book.
- Not sure what other scheduling analysis methods are there. Is there a good
overview available? 
- What is (your) preferred way dealing with asyncronous events (with respect
to rma)?

Comments, hints ... about using RMA in general and with rtems are highly
welcome,

Peter

-- 
GMX - Die Kommunikationsplattform im Internet.
http://www.gmx.net