C subroutine to supply the time in seconds

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The second.c module contains a C routine that calls the timer.s routines to access the upper and lower register contents.

It returns a double-precision real value of time in seconds.

double second()
{
  int ts, tl, tu;

  ts = rtc_upper();     /* seconds                          */
  tl = rtc_lower();     /* nanoseconds                      */
  tu = rtc_upper();     /* Check for a carry from           */
  if (ts != tu)         /* the lower reg to the upper.      */
    tl = rtc_lower();   /* Recover from the race condition. */
  return ( tu + (double)tl/1000000000 );
}

The subroutine second() can be called from either a C routine or a FORTRAN routine.

Note: Depending on the length of time since the last system reset, the second.c module might yield a varying amount of precision. The longer the time since reset, the larger the number of bits of precision consumed by the whole-seconds part of the number. The technique shown in the first part of this appendix avoids this problem by performing the subtraction required to obtain an elapsed time before converting to floating point.