RT issues

Rene Wittmann Rene.B.Wittmann at informatik.stud.uni-erlangen.de
Thu Apr 14 11:21:16 CEST 2005


As I'm trying to implement a real-time application in DROPS, I still
have some questions on this topic. Maybe there's someone who can answer
them because I didn't find it described it the documentation...

1. The timer granularity seems to be set to 976 microsec. Is there a
special background for using this number or can I set it down (maybe
even to 10 microsec, which what be a good time resolution for my task)?
How can I set it? Or would it be stupid to set it to such a tiny value?

2. When looking at the rt_sched example in the hello-package: the
main-thread has a preempter-thread for recognizing timeslice overrun and
deadline misses. When does this preempter-thread recognize a TS overrun
or a deadline miss? Right after this event (so within the next time
resolution) or after the main-thread says that is has finished it's work
(meaning after a call to "l4_rt_next_reservation")?

3. How can the preempter-thread tell the main-thread to stop it's work
in case of a timeslice overrun or even a deadline miss?

4. Does the system allow a thread's scheduling like this: 
period-length  =  976 microsec, 
timeslice_mand = 9760 microsec, 
timeslice_opt  = 9760 microsec
(which would mean that the system had to reserve timeslices that don't
fit into one period...)


period-length  = 9760 microsec,
timeslice_mand = 4380 microsec,
timeslice_opt  = 4380 microsec
(which would mean that the system had to reserve all resources for this
(what would happen if another thread comes with a period_length of also
9760 microsec and a timeslice_mand = 6000 microsec? What would be the
system's behaviour?)

Other thing:
File system support: 

1. which filesystems are supported (reiserfs?)? 

2. Is there a way to have RT access to disk and accessing files this way? 
If so, how?

Thanks, Rene

More information about the l4-hackers mailing list