Help: Some rtems basic questions... sorry...

gregory.menke at gregory.menke at
Wed Jan 14 22:36:26 UTC 2004

=?iso-8859-1?Q?Alex?= writes:
 > Hi all, 
 > I am a beginner in the rtems kernell... I have reading some documents but I cant 
 > solution some doubts:
 > My doubts are:Does RTEMS has user space and kernell space?

No, its all a flat address space.  All the OS code exists as a library
that you link your code with.  The final output of the link step is a
binary image of some format appropriate to the board you run it on.

 > Does RTEMS suppoorts more than one process running at a time?

Not in the process-protection sense.  It more resembles a pthread
system; you can run lots of pthreads all within one program, each
pthread has a scheduling policy, etc...  It is possible to convince
some Unixy daemons to compile and run in RTEMS- they still think they
are running as processes.

 > Does RTEMS has memory protection? virtual address partitions?

Depends on the bsp.  Some implement a 1:1 paging model to catch bad
pointers, but there is no virtual memory as such.  Other bsp's simply
disable whatever mmu functionality may exist.  There is no protection
for bad pointers messing things up.  This is the price you pay in a
non-trapped OS but OTOH you also gain a lot of performance.

 > Does rtems supports interrupt nesting...?

Depends on the bsp, some might, many do not.  Usually the interrupt
service routine will service all pending interrupts whenever it
executes- and it might do so in some priority order, but each vector
is executed to completion before the next one is called.

 > Am trying the BSP for i686

Good luck,


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