/**
* Determines if message bits 0 - 47 pass the Fleetsync CRC checksum
* contained in bits 48 - 63, using a lookup table of CRC checksum values
* derived from the CRC-15 value, and verifies the message has even parity
*/
public static CRC check( RadioLog.Common.SafeBitArray msg )
{
CRC crc = CRC.UNKNOWN;
int calculated = 1; //Starting value
//Check even parity
if( msg.Cardinality() % 2 == 0 )
{
//Iterate bits that are set and XOR running checksum with lookup value
for (int i = msg.nextSetBit( 0 ); i >= 0 && i < 48; i = msg.nextSetBit( i+1 ) )
{
calculated ^= sCHECKSUMS[ i ];
}
if( calculated == getChecksum( msg ) )
{
crc = CRC.PASSED;
}
else
{
crc = CRC.FAILED_CRC;
}
}
else
{
crc = CRC.FAILED_PARITY;
}
return crc;
}
public void Receive(bool softBit)
{
if (mSampleCounter >= 0)
{
if (softBit)
{
mBitSet.SetBit(mSampleCounter);
}
else
{
mBitSet.ClearBit(mSampleCounter);
}
}
mSampleCounter++;
if (mSampleCounter >= mSymbolLength)
{
bool decision = mBitSet.Cardinality() >= mDecisionThreshold;
send(decision);
/* Shift timing left if the left bit in the bitset is opposite
* the decision and the right bit is the same */
if ((mBitSet[0] ^ decision) &&
(!(mBitSet[mSymbolLength - 1] ^ decision)))
{
sendTapEvent(mBitSet, Shift.LEFT, decision);
reset();
mSampleCounter--;
}
/* Shift timing right if the left bit is the same as the
* decision and the right bit is opposite */
else if ((!(mBitSet[0] ^ decision)) && (mBitSet[mSymbolLength - 1] ^ decision))
{
sendTapEvent(mBitSet, Shift.RIGHT, decision);
/* Last bit from previous symbol to pre-fill next symbol */
bool previousSoftBit = mBitSet[mSymbolLength - 1];
reset();
if (previousSoftBit)
{
mBitSet.SetBit(0);
}
mSampleCounter++;
}
/* No shift */
else
{
sendTapEvent(mBitSet, Shift.NONE, decision);
reset();
}
}
}