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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 gnuradio import gr
import pmt
# Details of the NGHam protocol taken from
# https://github.com/skagmo/ngham/blob/master/ngham.c
ngham_rs_sizes = [47, 79, 111, 159, 191, 223, 255]
ngham_non_rs_sizes = [47-16, 79-16, 111-16, 159-32, 191-32, 223-32, 255-32]
class ngham_remove_padding(gr.basic_block):
"""
Removes the padding on an NGHam packet
Also it automatically detects if RS check bytes are
still in the packet and removes them as well
"""
def __init__(self):
gr.basic_block.__init__(
self,
name='ngham_remove_padding',
in_sig=[],
out_sig=[])
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)
if len(packet) in ngham_rs_sizes:
size_idx = ngham_rs_sizes.index(len(packet))
packet = packet[:ngham_non_rs_sizes[size_idx]]
if len(packet) not in ngham_non_rs_sizes:
print('NGHam packet length invalid')
return
padding = packet[0] & 0x1f
packet = packet[:-padding]
self.message_port_pub(
pmt.intern('out'),
pmt.cons(pmt.car(msg_pmt), pmt.init_u8vector(len(packet), packet)))
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