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# Copyright 2025 Fabian P. Schmidt <kerel@mailbox.org>
#
# This file is part of gr-satellites
#
# SPDX-License-Identifier: GPL-3.0-or-later
"""
References:
[1]: TechnoSat_TUBIN_Telemetry_Format
<https://www.static.tu.berlin/fileadmin/www/10002275/
Amateur_Radio/TechnoSat_Telemetry_Format.ods>
[2]: <https://destevez.net/2016/09/some-notes-on-beesat-and-mobitex-nx/>
"""
from gnuradio import gr
import pmt
from .check_eseo_crc import crc16_ccitt_zero as crc16_ccitt_zero
class tubix20_reframer(gr.basic_block):
"""
Input:
PDUs with decoded mobitex data blocks.
Each PDU must have a 'block id' tag.
The first PDU must have the following additional tags:
- 'num_blocks' tag: Number of blocks for this frame
- 'frame_header' tag: Header of this frame (typically 11 bytes)
- 2 control bytes
- 1 control bytes FEC
- 6 callsign bytes
- 2 callsign CRC bytes
Output:
PDUs with Tubix20 "Master Frames"
- master frame header (typically 10 bytes)
- 2 control bytes
- 6 callsign bytes
- 2 callsign CRC bytes
- master frame body
- N x 18 bytes
- master frame appendix
- 1 byte "ground station quality byte", placeholder value: 0xAA
- 4 bytes "error marker"
- 1 byte "ground station TNC temperature", placeholder value: 0xBB
"""
bytemap = {
'control_bytes': slice(0, 2),
'control_bytes_crc': slice(2, 3),
'callsign': slice(3, 9),
'callsign_crc': slice(9, 11),
}
def __init__(self):
gr.basic_block.__init__(
self,
name='tubix20_reframer',
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'))
self.reset()
def reset(self):
self.num_blocks_expected = 0
self.frame_header = None
self.block0_meta = None
self.blocks = {}
self.tags = {}
self.timestamp = None
def handle_msg(self, msg_pmt):
meta = pmt.car(msg_pmt)
packet = pmt.u8vector_elements(pmt.cdr(msg_pmt))
tags = pmt.to_python(meta)
# Reset state on block 0
if tags['block_id'] == 0:
if len(self.blocks) != 0:
print('ERROR: Received new block 0 while there are still '
'unhandled blocks in the buffer.')
# Discard partial frame
self.reset()
self.num_blocks_expected = tags['num_blocks']
self.frame_header = tags['frame_header']
tags_to_consume = ['block_id', 'frame_header', 'crc_valid',
'corrected_errors', 'uncorrected_errors']
for key in tags_to_consume:
meta = pmt.dict_delete(meta, pmt.intern(key))
self.block0_meta = meta
# Store in buffer
self.blocks[tags['block_id']] = packet
self.tags[tags['block_id']] = tags
if tags['block_id'] == self.num_blocks_expected - 1:
if (
(len(self.blocks) != self.num_blocks_expected) or
(self.frame_header is None)
):
print('ERROR: Unexpected number of data blocks, discard '
'partial frame.')
return
self.publish_frame()
self.reset()
def error_code_bytes(self):
"""
Returns the errorcode.
> This errorcode is a 32-bit bit-field that indicates which blocks
> are invalid. The bits that are set indicate an invalid block.
> The errorcode is in little-endian format, so the bit number 0 of
> the fist byte of the error code corresponds to the first data block
> and so on.
"""
error_code = 0
for block_id, tags in self.tags.items():
if not tags['crc_valid']:
error_code |= (1 << block_id) # Set bit for invalid block
pass
error_code_bytes = error_code.to_bytes(4, byteorder='little')
return error_code_bytes
def prepare_frame(self):
packet_out = []
# note: Based on convention,
# control_bytes_crc IS NOT added to the master frame header,
# but callsign_crc IS added to the master frame header.
packet_out.extend(self.frame_header[self.bytemap['control_bytes']])
packet_out.extend(self.frame_header[self.bytemap['callsign']])
packet_out.extend(self.frame_header[self.bytemap['callsign_crc']])
for i in range(len(self.blocks)):
packet_out.extend(self.blocks[i])
packet_out.extend([0xAA])
packet_out.extend(list(self.error_code_bytes()))
packet_out.extend([0xBB])
return packet_out
def publish_frame(self):
packet_out = self.prepare_frame()
num_blocks_correct = sum(
[1 for tags in self.tags.values() if tags['crc_valid']])
num_corrected_errors = sum(
[tags['corrected_errors'] for tags in self.tags.values()])
num_uncorrected_errors = sum(
[tags['uncorrected_errors'] for tags in self.tags.values()])
meta = pmt.dict_add(
self.block0_meta,
pmt.intern('num_blocks_correct'),
pmt.from_long(num_blocks_correct),
)
meta = pmt.dict_add(
meta,
pmt.intern('num_corrected_errors'),
pmt.from_long(num_corrected_errors),
)
meta = pmt.dict_add(
meta,
pmt.intern('num_uncorrected_errors'),
pmt.from_long(num_uncorrected_errors),
)
self.message_port_pub(
pmt.intern('out'),
pmt.cons(meta, pmt.init_u8vector(len(packet_out), packet_out)))
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