gps.py

import struct
from charstuffer import stuff
import xdata

'''
    UDP listens for a HELLO packet from HXr
    Format:
        HELLO
        --> 7e frame flag
        --> 5b vendor protocol code
        --> 01 source=1 (Primary ID)
        --> ff destination=255 (broadcast)
        --> 0a TTL=10
        --> 00 packet type=0 (hello)
        --> 01 link version=1
        --> 00 serial number=1
        --> 01 (LSB of serial number)
        --> 94 checksum=0x7f94
        --> 7f (MSB of checksum)
        --> 7e frame flag


    protocol = data[1]
    source = data[2]
    destination = data[3]
    ttl = data[4]
    packet_type = data[5]
    payload = data[6:-3]
    checksum = data[-3:-1].hex()
   
Packet type 9.
Byte 0: 0 (GPS position packet)
Byte 1: Last two digits of year (year mod 100), zero if unknown
Byte 2-5: packed LSB first: month (4 bits) | day (5 bits) | hour (5 bits) | min (6 bits) | sec (6 bits) | status (1 bit)
The date and time fields are all zeroes if unknown.
The status bit is 1 when the GPS has indicated its data is valid.
The EFIS may try to use this data as a time source if the day is non-zero and status is 1.
Byte 6-9: latitude (32-bit float)
Byte 10-13: longitude (32-bit float)
Byte 14-15: Ground track in tenths of a degree, MSB first
Byte 16-17: Magnetic variation in hundredths of a degree, MSB first, positive west
Byte 18-19: Ground speed in tenths of a knot, MSB first
Byte 20: bit field
Bit 0 = GPS2 input is configured on this unit
Bit 1 = This data is from GPS2
'''

def gps(): #latlong are floats.  track/magvar/gndspeed are short

    protocol = 91
    source = 1
    destination = 255
    ttl = 10
    packet_type = 9
    subpacket_type = 0
    year = 20
    
    track = int(xdata.headingt*10)
    magvar = int(xdata.magvar*100) 
    gndspeed = int(xdata.gndspeed*10*1.94384)
    
    
    #status = '1'
    #latitude = 47.12345 #32 bit float f
    #longitude = -122.12345 #32 bit float f
    #track = = 3590 #ground track in tenths, h
    #magvar = -1700 #magvar in hundreths, pos west, h
    #gndspeed = 2300 #groundspeed in tenths, MSB first, h
    bits = 0
    '''
    month = time & 15
    day = (time >> 4) & 31
    hour = (time >> 9) & 31
    minute = (time >> 14) & 63
    sec = (time >> 20) & 63
    status = (time >> 26) & 1
    '''
    time = 94153577
    #'7e5b01ff0a09001369ab9c0552fd3c424e36f5c2000dfa06055e00c4a37e'
    #payload = data[6:-3]
    #checksum = data[-3:-1].hex()
    #print(data)
    #payload = struct.pack("7BIff", protocol, source, destination, ttl, packet_type, subpacket_type, year, time, latitude, longitude)
    
    payload = struct.pack("7B", protocol, source, destination, ttl, packet_type, subpacket_type, year)
    payload2 = struct.pack("Iff", time, xdata.latitude, xdata.longitude)
    payload3= struct.pack(">Hhhb", track, magvar, gndspeed, bits)
    #print(payload.hex())
    #print(payload2.hex())
    #print(payload3.hex())    
    message = stuff((payload+payload2+payload3).hex())
    return message


def eis():
    protocol = 91
    source = 1
    destination = 255
    ttl = 10
    packet_type = 16
    
    #convert and scale variables
    volts = xdata.volts * 10
    hobbs = xdata.hobbs / 360
    fuelqty = xdata.fuelqty * 22 / 6
    flight_hrs = xdata.flighttime / 3600
    flight_min = (xdata.flighttime % 3600) / 60
    flight_sec = (xdata.flighttime % 3600) % 60


    #construct payload
    preamble = struct.pack("5B", protocol, source, destination, ttl, packet_type)
    part1 = struct.pack(">H6H9Hhf", xdata.rpm, xdata.cht, xdata.cht, xdata.cht, xdata.cht, 0,0, xdata.egt, xdata.egt, xdata.egt, xdata.egt, 0,0,0,0,0, xdata.airspeed, xdata.altitude)
    part2 = struct.pack(">ffhfhhbHhhHhh", volts, fuelflow, 0, xdata.vspeed, xdata.oat, xdata.oiltemp, xdata.oilpressure, xdata.manifoldpressure, 0, 0, xdata.fuelpressure, 0, 0)
    part3 = struct.pack(">bffcccbbfbhbb", 0, hobbs, fuelqty, flight_hrs, flight_min, flight_sec, 0x2c, 0x2c, xdata.baropressure, 0, 0, 0, 0x3b)
    
    message = stuff((preamble + part1 + part2 + part3).hex())
    
    return message