clock_gettime() result going backwards on LEON3?

[Miller, Scott A.]

Hello,

I'm observing that intermittently, that two successive calls to clock_gettime() will result in the 2nd timespec result being "before" the 1st timespec result.

Here's the code and some example output showing this:

<code snippet>

#include <rtems.h>
#include <bsp.h>
#define CONFIGURE_INIT

rtems_task Init(rtems_task_argument ignored);

#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_NULL_DRIVER      1
#define CONFIGURE_INIT_TASK_ATTRIBUTES               RTEMS_FLOATING_POINT
#define CONFIGURE_INIT_TASK_STACK_SIZE               (10 * RTEMS_MINIMUM_STACK_SIZE)
#define CONFIGURE_MAXIMUM_TASKS                      13
#define CONFIGURE_RTEMS_INIT_TASKS_TABLE
#define CONFIGURE_MAXIMUM_DRIVERS                    16
#define CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS     32
#define CONFIGURE_EXTRA_TASK_STACKS                  (10 * RTEMS_MINIMUM_STACK_SIZE)
#define CONFIGURE_MAXIMUM_POSIX_MUTEXES              rtems_resource_unlimited(10)
#define CONFIGURE_MAXIMUM_POSIX_CONDITION_VARIABLES  rtems_resource_unlimited(10)
#define CONFIGURE_MAXIMUM_POSIX_SEMAPHORES           rtems_resource_unlimited(10)
#define CONFIGURE_UNIFIED_WORK_AREAS
#include <rtems/confdefs.h>

....

    struct timespec time1;
    struct timespec time2;
    uint32_t i = 0;

    while (TRUE) {
        clock_gettime(CLOCK_REALTIME, &time1);
        clock_gettime(CLOCK_REALTIME, &time2);

        if (time1.tv_sec == time2.tv_sec) {
            if (time2.tv_nsec < time1.tv_nsec) {
                PRINTF("Violation!\n");
                PRINTF("%09u - %09u\n", time1.tv_sec, time1.tv_nsec);
                PRINTF("%09u - %09u\n", time2.tv_sec, time2.tv_nsec);
            }
        }

        i++;

        if (0 == (i % 1000)) {
            PRINTF("Completed %d iterations...\n", i);
        }
    }

</code snippet>

<output>

(gdb) run
Completed 1000 iterations...
Completed 2000 iterations...
Completed 3000 iterations...
Violation!
000000000 - 169994000
000000000 - 160002000
Completed 4000 iterations...
Completed 5000 iterations...
Completed 6000 iterations...
Violation!
000000000 - 409994000
000000000 - 400002000
Completed 7000 iterations...
Completed 8000 iterations...
Completed 9000 iterations...
Completed 10000 iterations...
Completed 11000 iterations...
Violation!
000000000 - 769993000
000000000 - 760001000

</output>

I'm running RTEMS 4.10.99 against the LEON3 (GR712RC) BSP.  

Is this expected behavior, or am I doing something incorrectly?

Thanks.

Scott

--

Scott Miller | 210-522-4249 | Senior Research Engineer | Southwest Research Institute