Rate monotonic help
Joel Sherrill
joel.sherrill at OARcorp.com
Mon Jul 25 20:19:25 UTC 2011
On 07/25/2011 03:14 PM, Gedare Bloom wrote:
> Lee,
>
> I have reproduced your problem.
>
> Put this line at the end of your Init function:
>
> status = rtems_task_delete( RTEMS_SELF );
>
> That should fix it.
>
Good eye! I was focused on the strange rate
so much that I missed that.
Lee.. When using the Classic API returning from
a task body is a fatal error. You halted the app. :-D
POSIX thread implicitly exit at that point.
Different behaviours because of different standards
and different programming view points.
--joel
> -Gedare
>
> On Mon, Jul 25, 2011 at 4:08 PM, Joel Sherrill
> <joel.sherrill at oarcorp.com> wrote:
>> On 07/25/2011 02:51 PM, Matthews, Lee wrote:
>>> Hi Joel,
>>>
>>> Thanks for your reply. I set the clock tick using :
>>>
>>> #define CONFIGURE_MICROSECONDS_PER_TICK 8195
>>>
>>> Basically, I'm working on a digital filter and I need a function to
>>> execute every 8.195ms (or 122Hz), hence the above value.
>>>
>>> I was indeed aiming for a tick to equal 1/122 of a second. Please excuse
>>> my noob question, but why do you think that that can't be right? By setting
>>> it to this value am I messing up the correct functioning of RTEMS?
>>>
>> It won't change the functioning but the clock tick is
>> the basis for all timeouts and delays. So all of your
>> timeouts will be in terms of 1/122 of a second.
>>
>> If that works as a reasonable common divisor for every
>> timing loop or delay in the system, then all is OK. You just
>> often see rates like 100Hz, 1000Hz, etc. and those are
>> just match up nicely with this clock tick rate. :)
>>
>> But for rate monotonic periods, it should be OK since
>> the task (assuming all preemptive and this is highest
>> priority) will run first after each clock tick.
>>
>> *** This is all a balancing act of the timing ***
>> *** granularity requirements of the set of tasks ***
>> *** in your application. There is no universally ***
>> *** right or wrong answer. ***
>>
>> FWIW Depending on RTEMS version, you will be able to
>> get time of day down to the nanosecond though.
>>
>> --joel
>>> Best wishes,
>>> Lee
>>> ________________________________________
>>> From: Joel Sherrill [joel.sherrill at oarcorp.com]
>>> Sent: 25 July 2011 18:50
>>> To: Matthews, Lee
>>> Cc: 'rtems-users at rtems.org'
>>> Subject: Re: Rate monotonic help
>>>
>>> What is your clock tick configured as? This is the
>>> CONFIGURE_MICROSECONDS_PER_TICK configuration
>>> parameter.
>>>
>>> FWIW your code assumes that 1 tick == 1/122 of
>>> a second from what I can tell and that can't be
>>> right.
>>>
>>> --joel
>>>
>>> On 07/25/2011 12:44 PM, Matthews, Lee wrote:
>>>> Hi
>>>>
>>>> I’m developing some software that uses RTEMS on an Aeroflex Gaisler
>>>> LEON3 processor that is running on a Pender GR-CPCI-AX2000 development
>>>> board.
>>>>
>>>> I’d like to setup a task that is called 122 times per second. I’m
>>>> currently trying to use the rtems rate_monotonic functions but I’m not
>>>> having much luck.
>>>>
>>>> I have used the example code from the rtems_user_guide as a guide.
>>>>
>>>> My function looks like the following :
>>>>
>>>> rtems_task Periodic_task()
>>>>
>>>> {
>>>>
>>>> rtems_name name;
>>>>
>>>> rtems_id period;
>>>>
>>>> rtems_status_code status;
>>>>
>>>> unsigned int flag=0;
>>>>
>>>> unsigned long count=0;
>>>>
>>>> unsigned int i=0;
>>>>
>>>> printf( "Starting periodic function : 61Hz clock output.\n");
>>>>
>>>> printf( "Turning GPIO OFF.\n");
>>>>
>>>> gpiolib_set(port1,1,0); // Set GPIO0 to OFF
>>>>
>>>> for(count=0;count<1000000;count++) {}
>>>>
>>>> printf( "Exiting wait loop.\n");
>>>>
>>>> name = rtems_build_name( 'P', 'E', 'R', 'D' );
>>>>
>>>> status = rtems_rate_monotonic_create( name,&period );
>>>>
>>>> if ( status != RTEMS_SUCCESSFUL ) {
>>>>
>>>> printf( "rtems_monotonic_create failed with status of
>>>> %d.\n", status );
>>>>
>>>> exit( 1 );
>>>>
>>>> }
>>>>
>>>> while ( 1 ) // RTEMS ticks per second set to 122.
>>>>
>>>> {
>>>>
>>>> if ( rtems_rate_monotonic_period( period, 1 ) ==
>>>> RTEMS_TIMEOUT ) break;
>>>>
>>>> /* Perform some periodic actions */
>>>>
>>>> if(flag==0)
>>>>
>>>> {
>>>>
>>>> gpiolib_set(port1,1,1); // Set GPIO0 to ON
>>>>
>>>> flag=1;
>>>>
>>>> }
>>>>
>>>> else
>>>>
>>>> {
>>>>
>>>> gpiolib_set(port1,1,0); // Set GPIO0 to OFF
>>>>
>>>> flag=0;
>>>>
>>>> }
>>>>
>>>> }
>>>>
>>>> /* missed period so delete period and SELF */
>>>>
>>>> status = rtems_rate_monotonic_delete( period );
>>>>
>>>> if ( status != RTEMS_SUCCESSFUL ) {
>>>>
>>>> printf( "rate_monotonic_delete failed with status of
>>>> %d.\n", status );
>>>>
>>>> exit( 1 );
>>>>
>>>> }
>>>>
>>>> status = rtems_task_delete( RTEMS_SELF );
>>>>
>>>> /* should not return */
>>>>
>>>> printf( "rtems_task_delete returned with status of %d.\n", status
>>>> );
>>>>
>>>> exit(1);
>>>>
>>>> }
>>>>
>>>> I’d like for the function to turn one of the GPIO lines on and off
>>>> repeatedly, but all that seems to happen is that the code within the
>>>> while ( 1 ) loop executes once, then stops.
>>>>
>>>> The code that I use to create and start this task is the following :
>>>>
>>>> Task_name1 = rtems_build_name( 'P', 'E', 'R', 'D' ); // Set task name
>>>> to 'PERD'
>>>>
>>>> status = rtems_task_create(Task_name1, 1,
>>>> RTEMS_MINIMUM_STACK_SIZE * 2,
>>>> RTEMS_DEFAULT_MODES,RTEMS_DEFAULT_ATTRIBUTES,&Task_id1);
>>>>
>>>> if(status!=RTEMS_SUCCESSFUL)
>>>>
>>>> {
>>>>
>>>> printf("rtems_task_create
>>>> unsuccesful\n");
>>>>
>>>> exit( 0 ); // Exit
>>>>
>>>> }
>>>>
>>>> else
>>>>
>>>> printf("Created Periodic task\n");
>>>>
>>>> status = rtems_task_start( Task_id1, Periodic_task, 1
>>>> ); // Start Periodic task
>>>>
>>>> if(status!=RTEMS_SUCCESSFUL)
>>>>
>>>> {
>>>>
>>>> printf("rtems_task_start unsuccesful\n");
>>>>
>>>> exit( 0 ); // Exit
>>>>
>>>> }
>>>>
>>>> Could anyone shed some light on what I’m doing wrong please?
>>>>
>>>> Thanks in advance,
>>>>
>>>> Lee
>>>>
>>> --
>>> Joel Sherrill, Ph.D. Director of Research& Development
>>> joel.sherrill at OARcorp.com On-Line Applications Research
>>> Ask me about RTEMS: a free RTOS Huntsville AL 35805
>>> Support Available (256) 722-9985
>>>
>>>
>>
>> --
>> Joel Sherrill, Ph.D. Director of Research& Development
>> joel.sherrill at OARcorp.com On-Line Applications Research
>> Ask me about RTEMS: a free RTOS Huntsville AL 35805
>> Support Available (256) 722-9985
>>
>>
>> _______________________________________________
>> rtems-users mailing list
>> rtems-users at rtems.org
>> http://www.rtems.org/mailman/listinfo/rtems-users
>>
--
Joel Sherrill, Ph.D. Director of Research& Development
joel.sherrill at OARcorp.com On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
Support Available (256) 722-9985
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