Support for fractional seconds in epoch definition

[jonathan-brandenburg-metecs]

Would a change to accept fractional seconds for the time epoch be accepted into cFE?

cFE supports setting the epoch of time with a granularity of seconds. Here is a relevant extract from sample_mission_cfg.h:

/**
**  \cfetimecfg Default EPOCH Values
**
**  \par Description:
**      Default ground time epoch values
**      Note: these values are used only by the CFE_TIME_Print() API function
**
**  \par Limits
**      Year - must be within 136 years
**      Day - Jan 1 = 1, Feb 1 = 32, etc.
**      Hour - 0 to 23
**      Minute - 0 to 59
**      Second - 0 to 59
*/
#define CFE_MISSION_TIME_EPOCH_YEAR   1980
#define CFE_MISSION_TIME_EPOCH_DAY    1
#define CFE_MISSION_TIME_EPOCH_HOUR   0
#define CFE_MISSION_TIME_EPOCH_MINUTE 0
#define CFE_MISSION_TIME_EPOCH_SECOND 0

It seems the definition of a commonly used epoch, J2000, contains fractional seconds: January 1, 2000, 11:58:55.816 UTC

As this issue is written, I've locally modified CFE_TIME_Print() to account for fractional seconds using a CFE_MISSION_TIME_EPOCH_MICROS macro, defined in this example to 816000. I have not yet written the unit tests. Here is a fragment from cfe_time_api.c:

    /*
    ** Convert the cFE time (offset from epoch) into calendar time...
    */
    NumberOfMicros = CFE_TIME_Sub2MicroSecs(TimeToPrint.Subseconds) + CFE_MISSION_TIME_EPOCH_MICROS;

    NumberOfMinutes = (NumberOfMicros / 60000000) + (TimeToPrint.Seconds / 60) + CFE_MISSION_TIME_EPOCH_MINUTE;
    NumberOfMicros = NumberOfMicros % 60000000;

    NumberOfSeconds = (NumberOfMicros / 1000000) + (TimeToPrint.Seconds % 60) + CFE_MISSION_TIME_EPOCH_SECOND;
    NumberOfMicros = NumberOfMicros % 1000000;

    /*
    ** Adding the epoch "seconds" after computing the minutes avoids
    **    overflow problems when the input time value (seconds) is
    **    at, or near, 0xFFFFFFFF...
    */

    while (NumberOfSeconds >= 60)
    {
        NumberOfMinutes++;
        NumberOfSeconds -= 60;
    }

[astrogeco]

CCB:2022-04-13

• rollover concerns need to make sure users stay within the bounds