Custom version of https://github.com/tomelec/RPi-LoRa-KISS-TNC
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280 lines
10 KiB
280 lines
10 KiB
# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# This program provides basic KISS AX.25 APRS frame encoding and decoding.
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# Note that only APRS relevant structures are tested. It might not work
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# for generic AX.25 frames.
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# 11/2019 by Thomas Kottek, OE9TKH
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#
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# Inspired by:
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# * Python script to decode AX.25 from KISS frames over a serial TNC
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# https://gist.github.com/mumrah/8fe7597edde50855211e27192cce9f88
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#
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# * Sending a raw AX.25 frame with Python
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# https://thomask.sdf.org/blog/2018/12/15/sending-raw-ax25-python.html
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#
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# TODO: remove escapes on decoding
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#
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# Changes by PE1RXF
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#
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# 2022-01-23: - in encode_address() added correct handling of has_been_repeated flag '*'
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# 2022-01-28: - in encode_kiss() and encode_address(): better exeption handling for corrupted or mal-formatted APRS frames
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#
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import struct
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KISS_FEND = 0xC0 # Frame start/end marker
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KISS_FESC = 0xDB # Escape character
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KISS_TFEND = 0xDC # If after an escape, means there was an 0xC0 in the source message
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KISS_TFESC = 0xDD # If after an escape, means there was an 0xDB in the source message
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# Addresses must be 6 bytes plus the SSID byte, each character shifted left by 1
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# If it's the final address in the header, set the low bit to 1
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# Ignoring command/response for simple example
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def encode_address(s, final):
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if b"-" not in s:
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s = s + b"-0" # default to SSID 0
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call, ssid = s.split(b'-')
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if len(call) < 6:
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call = call + b" "*(6 - len(call)) # pad with spaces
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encoded_call = [x << 1 for x in call[0:6]]
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encoded_ssid = 0b00000000
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# If ssid ends with *, the message has been repeated, so we have to set the 'has_been_repeated' flag and remove the * from the ssid
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if ssid[-1] == 42:
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# print("Message has been repeated")
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ssid = ssid[:-1]
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encoded_ssid |= 0b10000000
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# If SSID was not pressent (and we added the default -0 to it), the has_been_repeated flag could be at the end of the call, so check that as well
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# Also, there is a lot of bad software around (including this code) and ignorance of the specifications (are there any specs for LoRa APRS?), so always check for the has_been_repeated flag
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if call[-1] == 42:
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call = call[:-1]
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encoded_ssid |= 0b10000000
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# SSID should now be one or two postions long and contain a number (idealy between 0 and 15).
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if len(ssid) is 1 and ssid[0] > 47 and ssid[0] < 58:
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encoded_ssid |= (int(ssid) << 1) | 0b01100000 | (0b00000001 if final else 0)
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elif len(ssid) is 2 and ssid[0] > 47 and ssid[0] < 58 and ssid[1] > 47 and ssid[2] < 58:
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encoded_ssid |= (int(ssid) << 1) | 0b01100000 | (0b00000001 if final else 0)
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else:
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return None
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return encoded_call + [encoded_ssid]
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def decode_address(data, cursor):
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(a1, a2, a3, a4, a5, a6, a7) = struct.unpack("<BBBBBBB", data[cursor:cursor + 7])
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hrr = a7 >> 5
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ssid = (a7 >> 1) & 0xf
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ext = a7 & 0x1
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addr = struct.pack("<BBBBBB", a1 >> 1, a2 >> 1, a3 >> 1, a4 >> 1, a5 >> 1, a6 >> 1)
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if ssid != 0:
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call = addr.strip() + "-{}".format(ssid).encode()
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else:
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call = addr
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return (call, hrr, ext)
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########################################################################
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# Encode string from LoRa radio to AX.25 over KISS
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#
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# We must make no assumptions as the incomming frame could be carbage.
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# So make sure we think of everthing in order to prevent crashes.
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#
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# The original code from Thomas Kottek did a good job encoding propper APRS frames.
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# But when the frames where not what they should be, the program could crash.
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#
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########################################################################
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def encode_kiss(frame):
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# First check: do we have a semi column (seperator path field and data field)
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# Note that we could still be wrong: for example when the field seperator is corrupted and we now find a semi column from, lets say, an internet address in the data field...
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if not b":" in frame:
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return None
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# Split the frame in a path field and a data field
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path = frame.split(b":")[0]
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data_field = frame[frame.find(b":") + 1:]
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# The source address is always followed by a greather than sign, so lets see if its there.
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# There is always a change that there is another greather than sign because the frame could be corrupted...
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if not b">" in path:
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return None
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# Split the path into a source address and a digi-path array (because digis should be seperated by commas, but again, corruption....)
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src_addr = path.split(b">")[0]
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digis = path[path.find(b">") + 1:].split(b",")
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# destination address
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return_value = encode_address(digis.pop(0).upper(), False)
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if return_value is None:
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return None
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packet = return_value
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# source address
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return_value = encode_address(src_addr.upper(), len(digis) == 0)
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if return_value is None:
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return None
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packet += return_value
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# digipeaters
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for digi in digis:
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final_addr = digis.index(digi) == len(digis) - 1
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return_value = encode_address(digi.upper(), final_addr)
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if return_value is None:
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return None
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packet += return_value
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# control field
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packet += [0x03] # This is an UI frame
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# protocol ID
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packet += [0xF0] # No protocol
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# information field
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packet += frame[frame.find(b":") + 1:]
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# Escape the packet in case either KISS_FEND or KISS_FESC ended up in our stream
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packet_escaped = []
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for x in packet:
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if x == KISS_FEND:
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packet_escaped += [KISS_FESC, KISS_TFEND]
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elif x == KISS_FESC:
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packet_escaped += [KISS_FESC, KISS_TFESC]
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else:
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packet_escaped += [x]
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# Build the frame that we will send to Dire Wolf and turn it into a string
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kiss_cmd = 0x00 # Two nybbles combined - TNC 0, command 0 (send data)
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kiss_frame = [KISS_FEND, kiss_cmd] + packet_escaped + [KISS_FEND]
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try:
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output = bytearray(kiss_frame)
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except ValueError:
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print("Invalid value in frame.")
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return None
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return output
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def decode_kiss(frame):
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result = b""
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pos = 0
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if frame[pos] != 0xC0 or frame[len(frame) - 1] != 0xC0:
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print(frame[pos], frame[len(frame) - 1])
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return None
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pos += 1
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pos += 1
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# DST
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(dest_addr, dest_hrr, dest_ext) = decode_address(frame, pos)
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pos += 7
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# print("DST: ", dest_addr)
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# SRC
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(src_addr, src_hrr, src_ext) = decode_address(frame, pos)
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pos += 7
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# print("SRC: ", src_addr)
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result += src_addr.strip()
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# print(type(result), type(dest_addr.strip()))
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result += b">" + dest_addr.strip()
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# REPEATERS
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ext = src_ext
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while ext == 0:
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rpt_addr, rpt_hrr, ext = decode_address(frame, pos)
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# print("RPT: ", rpt_addr)
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pos += 7
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result += b"," + rpt_addr.strip()
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result += b":"
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# CTRL
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# (ctrl,) = struct.unpack("<B", frame[pos])
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ctrl = frame[pos]
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pos += 1
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if (ctrl & 0x3) == 0x3:
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#(pid,) = struct.unpack("<B", frame[pos])
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pid = frame[pos]
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# print("PID="+str(pid))
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pos += 1
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result += frame[pos:len(frame) - 1]
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elif (ctrl & 0x3) == 0x1:
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# decode_sframe(ctrl, frame, pos)
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print("SFRAME")
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return None
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elif (ctrl & 0x1) == 0x0:
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# decode_iframe(ctrl, frame, pos)
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print("IFRAME")
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return None
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return result
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class SerialParser():
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'''Simple parser for KISS frames. It handles multiple frames in one packet
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and calls the callback function on each frame'''
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STATE_IDLE = 0
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STATE_FEND = 1
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STATE_DATA = 2
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KISS_FEND = KISS_FEND
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def __init__(self, frame_cb=None):
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self.frame_cb = frame_cb
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self.reset()
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def reset(self):
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self.state = self.STATE_IDLE
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self.cur_frame = bytearray()
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def parse(self, data):
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'''Call parse with a string of one or more characters'''
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for c in data:
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if self.state == self.STATE_IDLE:
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if c == self.KISS_FEND:
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self.cur_frame.append(c)
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self.state = self.STATE_FEND
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elif self.state == self.STATE_FEND:
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if c == self.KISS_FEND:
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self.reset()
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else:
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self.cur_frame.append(c)
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self.state = self.STATE_DATA
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elif self.state == self.STATE_DATA:
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self.cur_frame.append(c)
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if c == self.KISS_FEND:
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# frame complete
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if self.frame_cb:
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self.frame_cb(self.cur_frame)
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self.reset()
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if __name__ == "__main__":
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# Playground for testing
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# frame = "\xc0\x00\x82\xa0\xa4\xb0dr`\x9e\x8ar\xa8\x96\x90u\x03\xf0!4725.73NR00939.61E&Experimental LoRa iGate\xc0"
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frame = "\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90q\x03\xf0!4725.51N/00939.86E[322/002/A=001306 Batt=3.99V\xc0"
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# print(decode_kiss(frame))
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# encoded = encode_kiss("OE9TKH-8>APRS,RELAY,BLA:!4725.51N/00939.86E[322/002/A=001306 Batt=3")
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# encoded = encode_kiss("OE9TKH-8>APRS,digi-3,digi-2:!4725.51N/00939.86E[322/002/A=001306 Batt=3")
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# print((decode_kiss(encoded)))
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# print((decode_kiss("\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90t\xae\x92\x88\x8ab@\x03\x03\xf0}OE9GHV-10>APMI06,TCPIP,OE9TKH-10*:@110104z4726.55N/00950.63E&WX3in1 op. Holger U=14.2V,T=8.8C\xc0")))
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def newframe(frame):
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print(repr(frame))
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two_example_frames = "\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90u\x03\xf0}SOTA>APZS16,TCPIP,OE9TKH-10*::OE9TKH-8 :<Ass/Ref> <Freq> <Mode> [call] [comment]{7ba\xc0\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90u\x03\xf0}SOTA>APZS16,TCPIP,OE9TKH-10*::OE9TKH-8 :/mylast{7bb\xc0\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90u\x03\xf0}SOTA>APZS16,TCPIP,OE9TKH-10*::OE9TKH-8 :/last{7bc\xc0\xc0\x00\x82\xa0\xa4\xa6@@`\x9e\x8ar\xa8\x96\x90u\x03\xf0}SOTA>APZS16,TCPIP,OE9TKH-10*::OE9TKH-8 :/time(/zone){7bd\xc0"
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sp = SerialParser(newframe)
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sp.parse(two_example_frames)
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