PNI SeaTRAX - Manual (Page 70)

PNI Sensor Corporation DOC#1018154 r02
SeaTRAX User Manual Page 65
crc ^= ((crc & 0xff) << 4) << 1;
}
return crc;
}
//
// This is called each time this process gets a turn to execute.
//
void CommProtocol::Control()
{
// InLen returns the number of bytes in the input buffer of
//the serial object that are available for us to read.
UInt32 inLen = mSerialPort->InLen();
switch(mStep)
{
case 1:
{
// wait for length bytes to be received by the serial object
if(inLen >= 2)
{
// Read block will return the number of requested (or available)
// bytes that are in the serial objects input buffer.
// read the byte count
mSerialPort->ReadBlock(mInData, 2);
// byte count is ALWAYS transmitted in big endian, copy byte
// count to mExpectedLen to native endianess
mExpectedLen = (mInData[0] << 8) |
mInData[1];
// Ticks is a timer function. 1 tick = 10msec.
// wait up to 1/2s for the complete frame (mExpectedLen) to be
// received
mTime = Ticks() + 50 ;
mStep++ ;
// goto the next step in the process
}
break ;
}
case 2:
{
// wait for msg complete or timeout
if(inLen >= mExpectedLen - 2)
{
UInt16 crc, crcReceived;
// calculated and received crcs.
// Read block will return the number of
// requested (or available) bytes that are in the
// serial objects input buffer.
mSerialPort->ReadBlock(&mInData[2],
mExpectedLen - 2);