Function offsetBetweenExtendedReadings

phc/offset.go:165–192

offsetBetweenExtendedReadings returns estimated difference between two PHC SYS_OFFSET_EXTENDED readings

(extendedA, extendedB *PTPSysOffsetExtended)

}

// generics in standard library can't come soon enough...
func abs(value time.Duration) time.Duration {
	if value < 0 {
		return -value
	}
	return value
}

// Sub returns the estimated difference between two PHC SYS_OFFSET_EXTENDED readings
func (extended *PTPSysOffsetExtended) Sub(a *PTPSysOffsetExtended) (time.Duration, error) {
	return offsetBetweenExtendedReadings(a, extended)
}

// Sub returns the estimated difference between two PHC SYS_OFFSET_PRECISE readings
func (precise *PTPSysOffsetPrecise) Sub(a *PTPSysOffsetPrecise) time.Duration {
	return offsetBetweenPreciseReadings(a, precise)
}

// offsetBetweenExtendedReadings returns estimated difference between two PHC SYS_OFFSET_EXTENDED readings
func offsetBetweenExtendedReadings(extendedA, extendedB *PTPSysOffsetExtended) (time.Duration, error) {
	// SYS_OFFSET_EXTENDED can provide different system clock, we can compare samples with same system clock id
	if extendedA.ClockID != extendedB.ClockID {
		return 0, fmt.Errorf("different system clock ids")
	}
	// we expect both probes to have same number of measures
	numProbes := min(int(extendedB.Samples), int(extendedA.Samples))
	// calculate sys time midpoint from both samples
	sysoffA := sysoffFromExtendedTS(extendedA.Ts[0])
	sysoffB := sysoffFromExtendedTS(extendedB.Ts[0])
	// offset between sys time midpoints
	sysOffset := sysoffB.SysTime.Sub(sysoffA.SysTime)