rtai priority marge

Jan Kiszka kiszka at rts.uni-hannover.de
Mon Oct 11 18:44:22 CEST 2004

Khaled Chaaban wrote:
> Hi,
> I would like to know if recent rtai versions supports 64 bits-based 
> priority, and if not, is it hard to make it on 64 bits?.
> P.S : on rtai-24.1.12, it's on 32 bits ( integer).

Well, I once read that having the need to use more than a handful 
priorities in your system indicates that you may have a real-time design 
problem. How do you manage such a bulk of priorities, 32 bits or even more?

I must confess that we also mess around with priorities in our robotic 
framework. We have some basic prio groups (actuators, critical control 
loops, important sensors), but we also assign sub-priorities to any 
component in the system making heavy use of that extremely large range 
of priorities (don't ask ME why...). It works as it should - but not 
because of the prios, it's because the system is effectively time-driven 
by the sensor capturing periods and control loop cycles.

Another aspect: Did you ever consider how an O(1) scheduler may look 
like with 64 bit-wide priorities (the same already applies to 32 bit)? 
How to sort so many levels in a load-independent way?


PS: As RTAI, as far as I remember, does not implicitely depend on that 
32 bits, extending the bit range by re-assigning some variable types 
should be easy...

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