Sending packet 0x6D corrupts the data. (0x6D - All-In-View Satellite Selection)

[sdroovan]

When creating a packet 0x6D and send it over RS232, it modifies the data incorrectly.

fixmode = (0x04 | ((g.num_sat)<<4))
command = tsip.Packet(0x6D, fixmode,0,0,0,0, *fields)				
gps_conn.write(command)

[mjuenema]

Hi, can you provide some more detail please. What is the expected outcome and what is the actual outcome?

[sdroovan]

Hi, I did some more debugging, and I guess the structure is not well defined.
See structs.py. Below you find the lines I corrected (see #<------).

class Struct0x6d(object):
    """Report Packet 0x6D: Satellite Selection List.

       This packet is of variable length equal to 5+nsvs where "nsvs" is
       the number of satellites used in the solution.

    """

    def pack(self, *f):
        fmt = '>BBffff' + 'b' * (len(f) - 6)                                             #<------
        return struct.pack(fmt, *f)

    def unpack(self, s):
        fields = [0x6d] + list(struct.unpack('>BBffff', s[1:18]))                        #<------
        nsvs = (fields[0] & 0b11110000) >> 4

        try:
            s = s[18:]
            for n in range(0, nsvs):
                fields.append(struct.unpack('>b', s[n])[0])
        except IndexError:
            # Occasionally `s` doesn't seem to be long enough
            # so in this case instead of causing an exception we
            # simply return the data so far.
            pass

        return fields

[mjuenema]

0x6d is an output packet which is a response to command packet 0x24. Is there a reason, why you want to send 0x6d?

[sdroovan]

I use it to simulate a gps receiver directly. So I just use the lib as a (gps) packet sender (not receiver).

[mjuenema]

Nice! I haven't thought of that. I am going to look into it.