rtems_semaphore_obtain

[Chris Xenophontos]

Hello all,

We have a situation, running RTEMS 4.6.0, on a Coldfire 5208.
One of the threads (tasks) in our application pends with a one-second
timeout on a semaphore released by an ISR.

The interrupt source that triggers the ISR (for this test case) runs every 3
seconds (~3.011).  This re-creates the problem more frequently.

Typically, the task will run, timeout once per second, unless the ISR is
triggered, in which case it will recognize it and process accordingly.  The
task processes critical values read from hardware that are latched by the
ISR.  99.99% of the time, it works as expected.  

As the ISR trigger "walks" close to the time of task timeout, we see the
back-to-back executions, as expected.

However, every 10 hours or so, the task will not respond to the semaphore
released from the ISR, even though debugging clearly shows the ISR responded
to the HW interrupt and latched the hardware values.  

The effect is a dropped interrupt - the rtems_semaphore_obtain call does not
return with an RTEMS_SUCCESSFUL status -- it returns a TIMEOUT.  No other
RTEMS error status are returned either (we check for these well).

The task, ISR, and semaphore_create function that we're using are listed
below.  Any help appreciated!!

Thanks
Chris Xenophontos

///////////// mytask//////////////////
mytask()
{
    while( 1 )
    {
    rtems_status = rtems_semaphore_obtain( &myIsrSemId, 
                                            RTEMS_WAIT, 
                                            100 );  // 100 ticks = 1 second 

    if(( rtems_status != RTEMS_SUCCESSFUL ) &&
       ( rtems_ststaus != RTEMS_TIMEOUT   ))
    {
       // post error status ( we NEVER see an error here )
    }

    if( rtems_status == RTEMS_SUCCESSFUL )
    {
        // do specific processing based on semaphore released by ISR
        ( not always seen, even though the ISR ran)
    }
    else
    {
        // specific processing based on timeout waiting for semaphore
    }
    }
}  
//////////////// end mytask///////////

the ISR is as follows
///////////////////myIsr////////////////
myIsr()
{
    ( code to ack the Colfire interrupt )...
    
    code to read 3 hardware registers....

    rtems_semaphore_release( &myIsrSemId );
}
///////////////myIsr///////////////////

the semaphore is created as follows, and is always created succesfully:

status = rtems_semaphore_create( "MISR",  0, 
( RTEMS_FIFO | RTEMS_NO_INHERIT_PRIORITY | RTEMS_SIMPLE_BINARY_SEMAPHORE |
RTEMS_NO_PRIORITY_CEILING | RTEMS_LOCAL ), 
RTEMS_NO_PRIORITY, &myIsrSemId )


mytask is created with the following attributes:
RTEMS_PREEMPT | RTEMS_NO_ASR | RTEMS_NO_TIMESLICE |
RTEMS_INTERRUPT_LEVEL(0),
RTEMS_FLOATING_POINT | RTEMS_LOCAL,

thanks,cx