00001 # Software License Agreement (BSD License) 00002 # 00003 # Copyright (c) 2013, Eric Perko 00004 # All rights reserved. 00005 # 00006 # Redistribution and use in source and binary forms, with or without 00007 # modification, are permitted provided that the following conditions 00008 # are met: 00009 # 00010 # * Redistributions of source code must retain the above copyright 00011 # notice, this list of conditions and the following disclaimer. 00012 # * Redistributions in binary form must reproduce the above 00013 # copyright notice, this list of conditions and the following 00014 # disclaimer in the documentation and/or other materials provided 00015 # with the distribution. 00016 # * Neither the names of the authors nor the names of their 00017 # affiliated organizations may be used to endorse or promote products derived 00018 # from this software without specific prior written permission. 00019 # 00020 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 00021 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 00022 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 00023 # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 00024 # COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 00025 # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 00026 # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 00027 # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 00028 # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 00029 # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 00030 # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 00031 # POSSIBILITY OF SUCH DAMAGE. 00032 00033 # Check the NMEA sentence checksum. Return True if passes and False if failed 00034 def check_nmea_checksum(nmea_sentence): 00035 split_sentence = nmea_sentence.split('*') 00036 if len(split_sentence) != 2: 00037 #No checksum bytes were found... improperly formatted/incomplete NMEA data? 00038 return False 00039 transmitted_checksum = split_sentence[1].strip() 00040 00041 #Remove the $ at the front 00042 data_to_checksum = split_sentence[0][1:] 00043 checksum = 0 00044 for c in data_to_checksum: 00045 checksum ^= ord(c) 00046 00047 return ("%02X" % checksum) == transmitted_checksum.upper() 00048 00049