[Bug 1748] New: LEON nanoseconds skipping back when called during timer tick

[bugzilla-daemon at rtems.org]

https://www.rtems.org/bugzilla/show_bug.cgi?id=1748

           Summary: LEON nanoseconds skipping back when called during
                    timer tick
           Product: RTEMS
           Version: unknown
          Platform: sparc
        OS/Version: RTEMS
            Status: NEW
          Severity: normal
          Priority: P3
         Component: bsps
        AssignedTo: joel.sherrill at oarcorp.com
        ReportedBy: rolf.schroedter at dlr.de


I'm running RTEMS on a LEON3 (sparc) platform.
It's downloaded from Gaisler and claims to be
     rtems-4.9.99.0(SPARC/w/FPU/leon3)

The function rtems_clock_get_uptime() fails when it
is called during a timer tick. In this case a single time value is
wrong, the time is skipping backwards by 1 millisecond (TICK). The next
call returns a correct time.

The problem can be demonstrated using the following code, storing the original
return of rtems_clock_get_uptime() in an array and calculating a  microsecond
value from that return. At the end all time values are printed showing the
problem:

Code:
RTEMS running with 1 millisecond TICK.
{
    #define LOOPS 1000

    int          i;
    uint32_t     uptime_usec[LOOPS], t0=0;
    struct timespec    uptime[LOOPS];

    for ( i=0; i<LOOPS; i++ )
    {
    rtems_clock_get_uptime( &uptime[i] );
    uptime_usec[i] = ((uint32_t)uptime[i].tv_sec * 1000000) +
((uint32_t)uptime[i].tv_nsec / 1000);
    }
    for ( i=0; i<LOOPS; i++ )
    {
    unsigned t1, usec, msec, sec;

    t1 = uptime_usec[i];
    usec = t1 % 1000;
    msec = (t1 / 1000) % 1000;
    sec  = t1 / 1000000;

    printf("TEST:rtems=%u.%09u   t=%u.%03u.%03u   dt=%u\n",
uptime[i].tv_sec, uptime[i].tv_nsec, sec, msec, usec, (t1-t0));
    t0 = t1;
    }
}


Output:
- Lines #616 and #686 show the time skipping backwards.
- The nanoseconds uptime shows that rtems_clock_get_uptime() has
probably been called during a clock TICK.

000: uptime=0.445817000   sec=0.445.817   dt=445817
001: uptime=0.445835000   sec=0.445.835   dt=18
002: uptime=0.445849000   sec=0.445.849   dt=14
003: uptime=0.445863000   sec=0.445.863   dt=14
...
616: uptime=0.454973000   sec=0.454.973   dt=14
617: uptime=0.454988000   sec=0.454.988   dt=15
618: uptime=0.454002000   sec=0.454.002   dt=4294966310
619: uptime=0.455042000   sec=0.455.042   dt=1040
620: uptime=0.455056000   sec=0.455.056   dt=14
621: uptime=0.455070000   sec=0.455.070   dt=14
...
684: uptime=0.455972000   sec=0.455.972   dt=14
685: uptime=0.455987000   sec=0.455.987   dt=15
686: uptime=0.455001000   sec=0.455.001   dt=4294966310
687: uptime=0.456042000   sec=0.456.042   dt=1041
688: uptime=0.456056000   sec=0.456.056   dt=14
689: uptime=0.456071000   sec=0.456.071   dt=15
...

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