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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright 2019 Daniel Estevez <daniel@destevez.net>
#
# This file is part of gr-satellites
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
from construct import *
SSID = BitStruct(
'ch' / Flag, # C / H bit
Default(BitsInteger(2), 3), # reserved bits
'ssid' / BitsInteger(4),
'extension' / Flag # last address bit
)
class CallsignAdapter(Adapter):
def _encode(self, obj, context, path=None):
return bytes([x << 1 for x in bytes(
(obj.upper() + ' '*6)[:6], encoding='ascii')])
def _decode(self, obj, context, path=None):
return str(bytes([x >> 1 for x in obj]), encoding='ascii').strip()
Callsign = CallsignAdapter(Bytes(6))
Address = Struct(
'callsign' / Callsign,
'ssid' / SSID
)
Control = Hex(Int8ub)
Control16 = Hex(Int16ub)
PID = Hex(Int8ub)
Header = Struct(
'addresses' / RepeatUntil(lambda x, lst, ctx: x.ssid.extension, Address),
'control' / Control,
'pid' / PID
)
Header16 = Struct(
'addresses' / RepeatUntil(lambda x, lst, ctx: x.ssid.extension, Address),
'control' / Control16,
'pid' / PID
)
Frame = Struct(
'header' / Header,
'info' / GreedyBytes
)
ax25 = Frame
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