Output syslink packets on pi

#!/usr/bin/python

import serial

from time import sleep

ser = serial.Serial("/dev/ttyS0", 115200)     # Open port with baud rate

MTU = 32

START_BYTE1 = 0xbc

START_BYTE2 = 0xcf

START = [START_BYTE1, START_BYTE2]

received_data = []

ser = serial.Serial("/dev/ttyS0", 115200)

while True:

#    received_data = ser.read()              # read serial port

#    sleep(0.03)

#    data_left = ser.inWaiting()             # check for remaining byte

#    received_data += ser.read(data_left)

#    print(list(received_data))              # print received data

#    ser.write(received_data)                # transmit data serially

    data_left = 1

    received_data = ""

    while data_left:

        received_data += ser.read()

        sleep(0.003)

        data_left = ser.inWaiting()

    print(list(received_data))

    received_data = map(ord, list(ser.read_until(chr(START_BYTE1))))

    received_data += map(ord, list(ser.read(1)))

    if received_data[1] != START_BYTE2:

        print("ERROR START")

        continue

    received_data += map(ord, list(ser.read(2)))

    if received_data[3] > MTU:

        print("ERROR LENGTH")

        continue

    received_data += map(ord, list(ser.read(received_data[3]+2)))

    cksum0 = 0

    cksum1 = 0

    for c in received_data[2:-2]:

        cksum0 = (cksum0 + c) & 0xff

        cksum1 = (cksum1 + cksum0) & 0xff

    if cksum0 != received_data[-2] or cksum1 != received_data[-1]:

        print("ERROR CKSUM")

    print(" ".join("{:#04x}".format(n) for n in received_data))