def unparse(self):
flag = bitarray.bitarray(endian="little")
flag.frombytes(self.flag)
bits = bitarray.bitarray(endian="little")
bits.frombytes(b"".join([self.header(), self.info, self.fcs()]))
data = flag + bit_stuff(bits) + flag
return data
def fcs(self):
content = bitarray.bitarray(endian="little")
content.frombytes(b"".join([self.header(), self.info]))
fcs = FCS()
for bit in content:
fcs.update_bit(bit)
# fcs.update(self.header())
# fcs.update(self.info)
return fcs.digest()
def fcs_validate(bits):
buffer = bitarray.bitarray()
fcs = FCS()
for bit in bits:
buffer.append(bit)
if len(buffer) > 16:
bit = buffer.pop(0)
fcs.update(bit)
yield bit
if buffer.tobytes() != fcs.digest():
raise Exception("FCS checksum invalid.")
def bit_unstuff(data):
count = 0
skip = False
ret_bits = bitarray.bitarray(endian="little")
for bit in data:
if not (skip):
if bit:
count += 1
else:
count = 0
ret_bits.append(bit)
if count == 5:
skip = True
count = 0
else:
skip = False
return ret_bits
def fcs(bits):
'''
Append running bitwise FCS CRC checksum to end of generator
'''
fcs = FCS()
for bit in bits:
yield bit
fcs.update_bit(bit)
# test = bitarray.bitarray()
# for byte in (digest & 0xff, digest >> 8):
# print byte
# for i in range(8):
# b = (byte >> i) & 1 == 1
# test.append(b)
# yield b
# append fcs digest to bit stream
# n.b. wire format is little-bit-endianness in addition to little-endian
digest = bitarray.bitarray(endian="little")
digest.frombytes(fcs.digest())
for bit in digest:
yield bit
def parse(self, bits):
flag = bitarray.bitarray(endian="little")
flag.frombytes(self.flag)
# extract bits from the first to second flag
try:
flag_loc = bits.search(flag)
bits_noflag = bits[flag_loc[0] + 8:flag_loc[1]]
# Bit unstuff
bits_unstuff = bit_unstuff(bits_noflag)
# Chop to length
bits_bytes = bits_unstuff.tobytes()
# Split bits
# header = bits_unstuff[:240]
h_dest = bits_unstuff[:56]
h_src = bits_unstuff[56:112]
for n in range(14, len(bits_bytes) - 1):
if bits_bytes[n:n + 2] == "\x03\xF0":
break
if n == len(bits_bytes) - 1:
self.destination = "no decode"
self.source = "no decode"
self.info = "no decode"
self.digis = "no decode"
return
digilen = (n - 14) * 8 / 7
h_digi = bits_unstuff[112:112 + (n - 14) * 8]
h_len = 112 + (n - 14) * 8 + 16
fcs = bits_unstuff[-16:]
info = bits_unstuff[h_len:-16]
# Split header
# protocol = header[-8:]
# control = header[-16:-8]
# address = header[:-16]
# Decode addresses
destination = self.callsign_decode(h_dest)
source = self.callsign_decode(h_src)
if digilen == 0:
digipeaters = ()
else:
digipeters = self.callsign_decode(h_digi)
# digipeaters = (self.callsign_decode(header[112:168]), self.callsign_decode(header[168:224]))
print("Destination:\t", destination[:-1])
print("Source:\t\t", source[:-1])
# print "Digipeater1:\t", digipeaters[0][:-1], "-", digipeaters[0][-1]
print("Digipeaters:\t", digipeaters)
print("Info:\t\t", info.tobytes())
self.destination = destination
self.source = source
self.info = info.tobytes()
self.digis = digipeaters
except:
self.destination = "no decode"
self.source = "no decode"
self.info = "no decode"
self.digis = "no decode"
return
def frame(stuffed_data):
return nrzi(
itertools.chain(
bitarray.bitarray("00000000") * PADDED_ZEROS,
bitarray.bitarray("01111110") * PADDED_FRAMES, stuffed_data,
bitarray.bitarray("01111110")))