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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright 2021-2022 Daniel Estevez <daniel@destevez.net>
#
# This file is part of gr-satellites
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
from gnuradio import gr, digital
import pmt
from ...hier.sync_to_pdu_packed import sync_to_pdu_packed
from ...hdlc_deframer import hdlc_crc_check
# HDLC 0x7e flag
_syncword = '01111110'
class crop_and_check_crc(gr.basic_block):
"""
Helper block to crop using the final 0x7e flag and check CRC-16
"""
def __init__(self):
gr.basic_block.__init__(
self,
name='crop_and_check_crc',
in_sig=[],
out_sig=[])
self.crc_check = hdlc_crc_check()
self.message_port_register_in(pmt.intern('in'))
self.set_msg_handler(pmt.intern('in'), self.handle_msg)
self.message_port_register_out(pmt.intern('out'))
def handle_msg(self, msg_pmt):
msg = pmt.cdr(msg_pmt)
if not pmt.is_u8vector(msg):
print('[ERROR] Received invalid message type. Expected u8vector')
return
packet = pmt.u8vector_elements(msg)
start = 0
while True:
try:
idx = packet[start:].index(0x7e)
except ValueError:
return
start += idx + 1
p = packet[:idx]
if self.crc_check.fcs_ok(p):
p = p[:-2]
self.message_port_pub(
pmt.intern('out'),
pmt.cons(pmt.PMT_NIL, pmt.init_u8vector(len(p), p)))
return
class yusat_deframer(gr.hier_block2):
"""
Hierarchical block to deframe YUSAT ad-hoc AX.25-like protocol
The input is a float stream of soft symbols. The output are PDUs
with YUSAT frames.
Args:
options: Options from argparse
"""
def __init__(self, options=None):
gr.hier_block2.__init__(
self,
'yusat_deframer',
gr.io_signature(1, 1, gr.sizeof_float),
gr.io_signature(0, 0, 0))
self.message_port_register_hier_out('out')
self.slicer = digital.binary_slicer_fb()
# We hope that 256 bytes is long enough to contain the full packet
self.deframer = sync_to_pdu_packed(
packlen=256, sync=_syncword, threshold=0)
self.crop = crop_and_check_crc()
self.connect(self, self.slicer, self.deframer)
self.msg_connect((self.deframer, 'out'), (self.crop, 'in'))
self.msg_connect((self.crop, 'out'), (self, 'out'))
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