[ECOS] Hard-Realtime behaviour

[Enno Luebbers]

Hi,

>> @Andrew : As we have seen most of what is necessary for hard realtime
>> behaviour of eCos already is implemented. Can you help me in  
>> figuring out
>> what is it that is missing that makes eCos soft real-time.
>
> What is missing? I would say the first step is to make a really good
> definition of what hard realtime is.

I think we can all agree that a real-time system is a deterministic  
system, i.e. it is _predictable_ in its timing behaviour. The  
distinction between hard and soft real-time, IMO, depends on the  
application. In a soft real-time system, some deadline misses can be  
tolerated - they only degrade the system's performance or service  
quality (think video streaming). On the other hand, a deadline miss  
in a hard real-time system causes a (catastrophic) system failure  
(think electronic brakes, engine control, etc).

So, if the OS routines in eCos are sufficiently predictable (so you  
can for example get upper bounds on the execution time) it's actually  
the application (read: the way the application programmer uses eCos  
services) that defines whether the system is hard or soft real-time.

Best,
- Enno


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