rtems_semaphore_obtain

[Eric Norum]

On Mar 22, 2007, at 4:23 AM, Sergei Organov wrote:
>
> I'd like first to understand why RTEMS_SIMPLE_BINARY_SEMAPHORE has  
> been
> implemented through kernel mutex in the first place. If there were no
> sound reasons, then I'd go with switching to implementation through
> kernel semaphore.
>

Correct me if I am wrong, but I was under the impression that a  
'classic' semaphore as described by Dijkstra (limited to values 1 and  
0) could be used successfully  for process synchronization or for  
mutual exclusion.  The only difference is in the way the semaphore is  
initialized.  If it starts out 'open' its semantics are that of a  
mutex.  If it starts out 'closed' its semantics are those of process  
synchronization.   Thus I don't see anything wrong with implementing  
RTEMS_SIMPLE_BINARY_SEMAPHORE with a core mutex.

Can you show in the RTEMS implementation of  
RTEMS_SIMPLE_BINARY_SEMAPHORE where the problem with releasing from  
an ISR occurs?  If so we should either fix what is broken or as you  
suggested change the RTEMS_SIMPLE_BINARY_SEMAPHORE implementation to  
use a core semaphore.    If there's no identifiable problem with the  
existing implementation I see no need to make any changes.

-- 
Eric Norum <norume at aps.anl.gov>
Advanced Photon Source
Argonne National Laboratory
(630) 252-4793