Tooltron

    printMsg(msg)

    bus.write(msg)

def sendData(t, data):

    body = chr(1) + chr(t) + TT_PROGD + data

    n = len(data)

    xor = 0

    for c in body:

        xor = xor ^ ord(c)

    msg = '^' + body + chr(xor)

    printMsg(msg)

    bus.write(msg)

            print 

        return TT_BAD

    if msg[0] != '^':

        return TT_BAD

    src = msg[1]

    #print "src: ", ord(src)

    r = readPacket()

    if r == TT_NACK:

        print "WARNING: got NACK, trying again"

        print "ERROR: got stray boot packet"

        #TODO: restart the whole state machine after the boot packet

        exit(-2)

        print "ERROR: got another packet:",r

        exit(-1)

        r = readPacket()

        if r == TT_NACK:

            print "WARNING: got NACK, trying again"

            print "ERROR: got stray boot packet"

            #TODO: restart the whole state machine after the boot packet

            exit(-2)

            print "ERROR: got another packet:",r

            exit(-1)