import serial, time

def fcs16(data):
    fcs = 0xFFFF
    for b in data:
        fcs = (fcs >> 8) ^ TAB[(fcs ^ b) & 0xFF]
    return (~fcs) & 0xFFFF

# build CRC-CCITT (reflected, 0x8408) table
TAB = []
for i in range(256):
    c = i
    for _ in range(8):
        c = (c >> 1) ^ 0x8408 if (c & 1) else (c >> 1)
    TAB.append(c)

def hdlc(payload):
    crc = fcs16(payload)
    frame = bytes(payload) + bytes([crc & 0xFF, (crc >> 8) & 0xFF])
    out = bytearray()
    for b in frame:
        if b == 0x7E: out += b'\x7d\x5e'
        elif b == 0x7D: out += b'\x7d\x5d'
        else: out.append(b)
    out.append(0x7E)
    return bytes(out)

def unhdlc(data):
    if not data: return data
    data = data.rstrip(b'\x7e')
    out = bytearray(); esc = False
    for b in data:
        if esc: out.append(b ^ 0x20); esc = False
        elif b == 0x7D: esc = True
        else: out.append(b)
    return bytes(out)

for dev in ['/dev/ttyUSB0','/dev/ttyUSB1']:
    try:
        s = serial.Serial(dev, 115200, timeout=1.5)
        s.reset_input_buffer()
        # DIAG_VERNO_F = 0x00
        s.write(hdlc([0x00]))
        time.sleep(0.4)
        r = s.read(256)
        print(dev, 'raw', r[:40].hex())
        dec = unhdlc(r)
        print('  decoded first byte:', hex(dec[0]) if dec else 'none', 'len', len(dec))
        s.close()
    except Exception as e:
        print(dev, 'ERR', e)