PNI CompassPoint Prime - Manual (Page 61)

Prime User Manual r08 Page 55
if(len > kBufferSize - kPacketMinSize) return;
// Store the total len of the packet including the len
// bytes(2), the frame ID(1), the data (len), and the crc (2).
// If no data is sent, the min len is 5
mOutData[index++] = count >> 8;
mOutData[index++] = count & 0xFF;
// store the frame ID
mOutData[index++] = frameType ;
// copy the data to be sent
while(len--) mOutData[index++] = *data++;
// compute and add the crc
crc = CRC(mOutData, index);
mOutData[index++] = crc >> 8 ;
mOutData[index++] = crc & 0xFF ;
// Write block will copy and send the data out the serial port
mSerialPort->WriteBlock(mOutData, index);
}
//
// Call the functions in serial port necessary to change the
// baud rate
//
void CommProtocol::SetBaud(UInt32 baud)
{
mSerialPort->SetBaudRate(baud);
// clear any data that was already waiting in the buffer
mSerialPort->InClear();
}
//
// Update the CRC for transmitted and received data using the
// CCITT 16bit algorithm (X^16 + X^12 + X^5 + 1).
//
UInt16 CommProtocol::CRC(void * data, UInt32 len)
{
UInt8 * dataPtr = (UInt8 *)data;
UInt32 index = 0;
UInt16 crc = 0;
while(len--)
{
crc = (unsigned char)(crc >> 8) | (crc << 8);
crc ^= dataPtr[index++];
crc ^= (unsigned char)(crc & 0xff) >> 4;
crc ^= (crc << 8) << 4;
crc ^= ((crc & 0xff) << 4) << 1;