[Bug 2180] New: _TOD_Get_with_nanoseconds() is broken on SMP

[Joel Sherrill]

On 8/20/2014 8:12 AM, Daniel Cederman wrote:
> Hi,
>
> We are currently experiencing this bug reported by Sebastian Huber and I 
> could not find any discussion on it on the list. I'm guessing that the 
> simple solution of moving the call to Clock_driver_support_at_tick() to 
> the critical section of _TOD_Tickle_ticks() is not an acceptable 
> solution, given that it would be a call from score to the BSP?
I don't have a problem with it. Some documentation may need to be updated to
reflect the environment in which the bsp hook is called but I think it
is pretty
obvious it is called when an accurate timestamp is wanted.

--joel
> Best regards,
> Daniel C
>
> On 2014-06-05 15:29, bugzilla-daemon at rtems.org wrote:
>> https://www.rtems.org/bugzilla/show_bug.cgi?id=2180
>>
>>               Bug #: 2180
>>             Summary: _TOD_Get_with_nanoseconds() is broken on SMP
>>      Classification: Unclassified
>>             Product: RTEMS
>>             Version: 4.11
>>            Platform: All
>>          OS/Version: RTEMS
>>              Status: NEW
>>            Severity: normal
>>            Priority: P3
>>           Component: cpukit
>>          AssignedTo: joel.sherrill at oarcorp.com
>>          ReportedBy: sebastian.huber at embedded-brains.de
>>
>>
>> We have
>>
>> Timestamp_Control *_TOD_Get_with_nanoseconds(
>>    Timestamp_Control *snapshot,
>>    const Timestamp_Control *clock
>> )
>> {
>>    TOD_Control      *tod = &_TOD;
>>    ISR_lock_Context  lock_context;
>>    Timestamp_Control offset;
>>    Timestamp_Control now;
>>    uint32_t          nanoseconds;
>>
>>    _TOD_Acquire( tod, &lock_context );
>>      nanoseconds = ( *tod->nanoseconds_since_last_tick )();
>>      now = *clock;
>>    _TOD_Release( tod, &lock_context );
>>
>>    _Timestamp_Set( &offset, 0, nanoseconds );
>>    _Timestamp_Add_to( &now, &offset );
>>
>>    *snapshot = now;
>>
>>    return snapshot;
>> }
>>
>> and
>>
>> void _TOD_Tickle_ticks( void )
>> {
>>    TOD_Control       *tod = &_TOD;
>>    ISR_lock_Context   lock_context;
>>    Timestamp_Control  tick;
>>    uint32_t           nanoseconds_per_tick;
>>
>>    nanoseconds_per_tick = rtems_configuration_get_nanoseconds_per_tick();
>>
>>    /* Convert the tick quantum to a timestamp */
>>    _Timestamp_Set( &tick, 0, nanoseconds_per_tick );
>>
>>    /* Update the counter of ticks since boot */
>>    _Watchdog_Ticks_since_boot += 1;
>>
>>    _TOD_Acquire( tod, &lock_context );
>>
>>    /* Update the uptime */
>>    _Timestamp_Add_to( &tod->uptime, &tick );
>>
>>    /* Update the current TOD */
>>    _Timestamp_Add_to( &tod->now, &tick );
>>
>>    _TOD_Release( tod, &lock_context );
>>
>>    _TOD.seconds_trigger += nanoseconds_per_tick;
>>    if ( _TOD.seconds_trigger >= 1000000000UL ) {
>>      _TOD.seconds_trigger -= 1000000000UL;
>>      _Watchdog_Tickle_seconds();
>>    }
>> }
>>
>> and (standard Clock driver)
>>
>> #if defined(BSP_FEATURE_IRQ_EXTENSION) || \
>>      (CPU_SIMPLE_VECTORED_INTERRUPTS != TRUE)
>> void Clock_isr(void *arg)
>> {
>> #else
>> rtems_isr Clock_isr(rtems_vector_number vector);
>> rtems_isr Clock_isr(
>>    rtems_vector_number vector
>> )
>> {
>> #endif
>>    /*
>>     *  Accurate count of ISRs
>>     */
>>    Clock_driver_ticks += 1;
>>
>>    #if CLOCK_DRIVER_USE_FAST_IDLE
>>      do {
>>        rtems_clock_tick();
>>      } while (
>>        _Thread_Heir == _Thread_Executing
>>          && _Thread_Executing->Start.entry_point
>>            == rtems_configuration_get_idle_task()
>>      );
>>
>>      Clock_driver_support_at_tick();
>>      return;
>>    #else
>>      /*
>>       *  Do the hardware specific per-tick action.
>>       *
>>       *  The counter/timer may or may not be set to automatically reload.
>>       */
>>      Clock_driver_support_at_tick();
>>
>>      #if CLOCK_DRIVER_ISRS_PER_TICK
>>        /*
>>         *  The driver is multiple ISRs per clock tick.
>>         */
>>        if ( !Clock_driver_isrs ) {
>>          rtems_clock_tick();
>>
>>          Clock_driver_isrs = CLOCK_DRIVER_ISRS_PER_TICK;
>>        }
>>        Clock_driver_isrs--;
>>      #else
>>        /*
>>         *  The driver is one ISR per clock tick.
>>         */
>>        rtems_clock_tick();
>>      #endif
>>    #endif
>> }
>>
>>
>> Suppose we are between Clock_driver_support_at_tick() and _TOD_Tickle_ticks().
>> Now call _TOD_Get_with_nanoseconds() on another processor.  With most
>> nanoseconds extensions we observe now a serviced hardware clock interrupt and
>> the old _TOD.uptime value.
>>
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-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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