GPS NMEA string generator

GPS.py

#!/usr/bin/env python

import numpy as np


def main():
    def ubx_checksum(data):
        ck_a = 0
        ck_b = 0
        for byte in data:
            ck_a = (ck_a + byte) & 0xFF
            ck_b = (ck_b + ck_a) & 0xFF

        return ck_a, ck_b

    # UBX-CFG-RATE (0x06 0x08)
    head0 = 0xB5
    head1 = 0x62

    Class = 0x06
    ID = 0x08

    length0 = 6
    length1 = 0

    # 10 Hz
    measRate0 = 100  # 100 ms
    measRate1 = 0

    # One measurement for every sample (default)
    navRate0 = 1
    navRate1 = 0

    # GPS time (default)
    timeRef0 = 1
    timeRef1 = 0

    msg = np.array([Class, ID, length0, length1,
                    measRate0, measRate1, navRate0, navRate1, timeRef0, timeRef1])

    assert((length1 << 8 | length0) == len(msg) - 4)

    checksum = ubx_checksum(msg)

    # Final message
    rate_msg = np.append(np.append([head0, head1], msg), checksum)

    print('uint8_t rate_msg[' + str(len(rate_msg)) + '] = { ' + ' '.join('0x{:02X},'.format(x) for x in rate_msg) + ' };')

    # Set baudrate:
    # gps_str = 'PUBX,41,1,0007,0002,38400,0'
    # gps_str = 'PUBX,41,1,0007,0002,57600,0'
    gps_str = 'PUBX,41,1,0007,0002,115200,0'
    # gps_str = 'PUBX,41,1,0007,0002,230400,0'
    # gps_str = 'PUBX,41,1,0007,0002,460800,0'

    # inRtcm - RTCM2 protocol (bit 2)
    # inNmea - NMEA protocol (bit 1)
    # inUbx - UBX protocol (bit 0)
    # inProtoMask = 7 (All)

    # outNmea - NMEA protocol (bit 1)
    # outUbx - UBX protocol (bit 0)
    # outProtoMask = 2 (NMEA only)

    checksum = 0
    for char in gps_str:
        checksum ^= ord(char)

    print('$' + gps_str + '*' + '{:02X}'.format(checksum) + '\\r\\n')

if __name__ == '__main__':
    main()