Function writeStartTime

GSM/GSML3GPRSElements.cpp:163–200

TBF Starting Time GSM 04.08 10.5.2.38

// TBF Starting Time GSM 04.08 10.5.2.38
static void writeStartTime(MsgCommon &dest, unsigned startframe)
{
	std::ostream*os = dest.getStream();	// non-NULL for text() function.

	// The names T1, T2, T3 are defined in table 10.5.79
	unsigned T1 = (startframe/1326)%32;
	unsigned T3 = startframe%51;
	unsigned T2 = startframe%26;

	// Recompute original startframe:
	// Note that T3-T2 may be negative:
	int recomputed = 51 * (((int)T3-(int)T2) % 26) + T3 + 51 * 26 * T1;
	unsigned startframemod = (startframe % 42432);

	// If we are writing text(), output both the original startframe and 
	// the computed T1,T2,T3.
	if (os) {
		// The recomputed time may be a much smaller number than startframe.
		*os << " TBFStartFrame=" <<startframe << "=(" << "T=" <<recomputed;
	}

	// Note: The fields are written here Most-Significant-Bit first in each byte,
	// then the bytes are reversed in the encoder before being sent to the radio.
	// 		 	7      6      5      4      3     2      1      0
	//	  [			T1[4:0]                 ][   T3[5:3]        ]  Octet 1
	//	  [       T3[2:0]     ][            T2[4:0]             ]  Octet 2
	dest.writeField(T1,5,"T1p");
	dest.writeField(T3,6,"T3");	// Yes T3 comes before T2.
	dest.writeField(T2,5,"T2");

	// This just doesnt work, despite the documentation.
	if (os && recomputed != (int)startframemod) {
		*os << " TBF Start Time miscalculation: "
			<<LOGVAR(startframemod) <<"!=" <<LOGVAR(recomputed);
	}

	if (os) { *os << ")"; }
}


// (pat) The uplink assignment is always initiated by the MS using a RACH,