checkflightmode.py

#calcuate expected UBX ACK packet and parse UBX response from GPS
def getUBX_ACK(MSG):
    
    b = 0
    ackByteID = 0
    ackPacket = [0 for x in range(10)]
    startTime = millis()
 
 
    print "Reading ACK response: "
        
    #construct the expected ACK packet
    ackPacket[0] = int('0xB5', 16) #header
    ackPacket[1] = int('0x62', 16) #header
    ackPacket[2] = int('0x05', 16) #class
    ackPacket[3] = int('0x01', 16) #id
    ackPacket[4] = int('0x02', 16) #length
    ackPacket[5] = int('0x00', 16)
    ackPacket[6] = MSG[2] #ACK class
    ackPacket[7] = MSG[3] #ACK id
    ackPacket[8] = 0 #CK_A
    ackPacket[9] = 0 #CK_B
 
 
    #calculate the checksums
    for i in range(2,8):
        ackPacket[8] = ackPacket[8] + ackPacket[i]
        ackPacket[9] = ackPacket[9] + ackPacket[8]
 
 
    #print expected packet
    print "Expected ACK Response: "
    for byt in ackPacket:
        print byt
                
    print "Waiting for UBX ACK reply:"
    while 1:
        #test for success
        if ackByteID > 9 :
            #all packets are in order
            print "ACK has been acknowledged successfully!"
            return True
 
 
        #timeout if no valid response in 3 secs
        if millis() - startTime > 3000:
            print "The ACK has completely failed"
            return False
        #make sure data is availible to read
        if GPS.inWaiting() > 0:
            print "serial buffer contains data"
            b = GPS.read(1)
            print "following byte has been read from buffer:", ord(b)
                   
                  
            #check that bytes arrive in the sequence as per expected ACK packet
            if ord(b) == ackPacket[ackByteID]:
                print "this particular byte matches our expected response"
                ackByteID += 1
                #print ord(b)
            else:
                ackByteID = 0 #reset and look again, invalid order
                print "the byte doesn't match what was expected. Back to the start"
            print "current ackByteID:", ackByteID