def decodeAX25(bits):
ax = ax25.AX25()
ax.info = "bad packet"
bitsu = ax25.bit_unstuff(bits[8:-8])
if (genfcs(bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()) == False:
#print("failed fcs")
return ax
bytes = bitsu.tobytes()
ax.destination = ax.callsign_decode(bitsu[:56])
source = ax.callsign_decode(bitsu[56:112])
if source[-1].isdigit() and source[-1]!="0":
ax.source = b"".join((source[:-1],'-',source[-1]))
else:
ax.source = source[:-1]
digilen=0
if bytes[14]=='\x03' and bytes[15]=='\xf0':
digilen = 0
else:
for n in range(14,len(bytes)-1):
if ord(bytes[n]) & 1:
digilen = (n-14)+1
break
# if digilen > 56:
# return ax
ax.digipeaters = ax.callsign_decode(bitsu[112:112+digilen*8])
ax.info = bitsu[112+digilen*8+16:-16].tobytes()
return ax
def detectFrames(NRZI):
# function looks for packets in an NRZI sequence and validates their checksum
# compute finite differences of the digital NRZI to detect zero-crossings
dNRZI = NRZI[1:] - NRZI[:-1]
# find the position of the non-zero components. These are the indexes of the zero-crossings.
transit = np.nonzero(dNRZI)[0]
# Transition time is the difference between zero-crossings
transTime = transit[1:]-transit[:-1]
# loop over transitions, convert to bit streams and extract packets
dict = { 1:bitarray.bitarray([0]), 2:bitarray.bitarray([1,0]), 3:bitarray.bitarray([1,1,0]),
4:bitarray.bitarray([1,1,1,0]),5:bitarray.bitarray([1,1,1,1,0]),6:bitarray.bitarray([1,1,1,1,1,0])
,7:bitarray.bitarray([1,1,1,1,1,1,0])}
state = 0; # no flag detected yet
packets =[]
tmppkt = bitarray.bitarray([0])
lastFlag = 0 # position of the last flag found.
for n in range(0,len(transTime)):
Nb = round(transTime[n]/36.75) # maps intervals to bits. Assume 44100Hz and 1200baud
if (Nb == 7 and state ==0):
# detected flag frame, start collecting a packet
tmppkt = tmppkt + dict[7]
state = 1 # packet detected
lastFlag = transit[n-1]
continue
if (Nb == 7 and state == 1):
# detected end frame successfully
tmppkt = tmppkt + dict[7]
# validate checksum
bitsu = ax25.bit_unstuff(tmppkt[8:-8]) # unstuff bits
if (genfcs(bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()) :
# valid packet
packets.append(tmppkt)
tmppkt = bitarray.bitarray([0])
state = 0
continue
if (state == 1 and Nb < 7 and Nb > 0):
# valid bits
tmppkt = tmppkt + dict[Nb]
continue
else:
# not valid bits reset
state = 0
tmppkt = bitarray.bitarray([0])
continue
if state == 0:
lastFlag = -1
# if the state is 1, which means that we detected a packet, but the buffer ended, then
# we return the position of the beginning of the flag within the buffer to let the caller
# know that there's a packet that overlapps between two buffer frames.
return packets, lastFlag
def decodeAX25(self,bits, deepsearch=False):
ax = ax25.AX25()
ax.info = "bad packet"
bitsu = ax25.bit_unstuff(bits[8:-8])
foundPacket = False
if (self.genfcs(bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()):
foundPacket = True
elif deepsearch:
tbits = bits[8:-8]
for n in range(0,len(tbits)):
tbits[n] = not tbits[n]
if (self.genfcs(bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()):
foundPacket = True
print("Success deep search")
break
tbits[n] = not tbits[n]
if foundPacket == False:
return ax
bytes = bitsu.tobytes()
ax.destination = ax.callsign_decode(bitsu[:56])
source = ax.callsign_decode(bitsu[56:112])
if source[-1].isdigit() and source[-1]!="0":
ax.source = b"".join((source[:-1],'-',source[-1]))
else:
ax.source = source[:-1]
digilen=0
if bytes[14]=='\x03' and bytes[15]=='\xf0':
digilen = 0
else:
for n in range(14,len(bytes)-1):
if ord(bytes[n]) & 1:
digilen = (n-14)+1
break
# if digilen > 56:
# return ax
ax.digipeaters = ax.callsign_decode(bitsu[112:112+digilen*8])
ax.info = bitsu[112+digilen*8+16:-16].tobytes()
return ax
def decodeAX25(self, bits, deepsearch=False):
ax = ax25.AX25()
ax.info = "bad packet"
bitsu = ax25.bit_unstuff(bits[8:-8])
foundPacket = False
if (self.genfcs(bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()):
foundPacket = True
elif deepsearch:
tbits = bits[8:-8]
for n in range(0, len(tbits)):
tbits[n] = not tbits[n]
if (self.genfcs(
bitsu[:-16]).tobytes() == bitsu[-16:].tobytes()):
foundPacket = True
print("Success deep search")
break
tbits[n] = not tbits[n]
if foundPacket == False:
return ax
bytes = bitsu.tobytes()
ax.destination = ax.callsign_decode(bitsu[:56])
source = ax.callsign_decode(bitsu[56:112])
source = str(source)
if source[-1].isdigit() and source[-1] != "0":
ax.source = b"".join((source[:-1], '-', source[-1]))
else:
ax.source = source[:-1]
digilen = 0
if bytes[14] == '\x03' and bytes[15] == '\xf0':
digilen = 0
else:
for n in range(14, len(bytes) - 1):
if bytes[n] & 1:
digilen = (n - 14) + 1
break
utils.print_msg("Digilen = " + str(digilen), DEBUG)
# if digilen > 56:
# return ax
ax.digipeaters = ax.callsign_decode(bitsu[112:112 + digilen * 8])
ax.info = bitsu[112 + digilen * 8 + 16:-16].tobytes()
return ax
def findPackets(bits, rs=reedsolo.RSCodec(NUM_ERRORS*2)):
if len(bits) == 0:
return []
flag = "01111110"
bitstream = iter(bits)
b = bitstream.next()
packets = []
while True:
try:
if b == 0:
for _ in range(6):
b = bitstream.next()
if b != 1:
break
else:
b = bitstream.next()
if b == 0:
# Flag found begin collecting data
data = bitarray.bitarray()
done = False
while not done:
for _ in range(8):
data.append(bitstream.next())
while data[-8:].to01() != flag:
data.append(bitstream.next())
if data[:8].to01() == flag:
data = data[8:]
if len(data[:-8]) > 16:
done = True
data = data[:-8]
data = ax25.bit_unstuff(data)
try:
# print "received", data
data = bitarray.bitarray(np.unpackbits(rs.decode(bytearray(bitarray.bitarray(data.to01()).tobytes()))).tolist())
# print "decoded ", data
if len(data) > 8 and checksum(data[:-8]) == data[-8:]:
packets.append(data[:-8])
except:
pass
# print "error"
# print data
else:
b = bitstream.next()
except StopIteration:
break
return packets
def checkPacket(bitstream, leftFlag, rightFlag, rs=reedsolo.RSCodec(NUM_ERRORS*2)):
# print leftFlag, rightFlag, bitstream[:16].to01(), bitstream[-16:].to01()
if leftFlag <= 0 or rightFlag <= 0:
# print "out of flag"
return None
try:
p = bitstream.copy()
p = ax25.bit_unstuff(p[8:-8])
p = bitarray.bitarray(np.unpackbits(rs.decode(bytearray(bitarray.bitarray(p.to01()).tobytes()))).tolist())
# print "decoded"
return p
except:
# print "decoding failed"
p = bitstream.copy()
p = checkPacket(p[8:], leftFlag - 1, rightFlag)
if p:
# print "gone left"
return p
p = checkPacket(p[:-8], leftFlag, rightFlag - 1)
if p:
# print "gone right"
return p
# print "recursion failed"
return None
