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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Copyright 2023 Daniel Estevez <daniel@destevez.net>
#
# This file is part of gr-satellites
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
import struct
from .imagereceiver import ImageReceiver
# Documentation:
# https://ukamsat.files.wordpress.com/2022/12/
# camsat-cas-5a-amateur-radio-satellite-users-manual-v2.0.pdf
class ImageReceiverCAS5A(ImageReceiver):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self._current_fid = -1
self._first_chunk = None
self._current_offset = 0
self._current_chunk = None
self._next_offset = 0
def parse_chunk(self, chunk):
# The AX.25 header occupies 16 bytes
if len(chunk) <= 16:
return None
chunk = chunk[16:]
if chunk.startswith(b'\x01\x00' * 3):
# Telemetry frames start by 01 00 01 00 01 00.
# The documentation says that they start by
# 01 00 01 00 01 00 7E,
# but they actually seem to start by
# 01 00 01 00 01 00 A7
return None
return chunk
def chunk_data(self, chunk):
return chunk
def chunk_offset(self, chunk):
# To determine the offset, we count how many bytes we've seen so far
# (this assumes we don't lose any chunks).
if self._current_chunk != chunk:
self._current_chunk = chunk
self._current_offset = self._next_offset
offset = self._current_offset
self._next_offset = offset + len(chunk)
return offset
def file_id(self, chunk):
# A new JPEG file starts by ff d8
if chunk.startswith(b'\xff\xd8') and chunk != self._first_chunk:
self._current_fid += 1
self._current_offset = 0
self._first_chunk = chunk
self._current_chunk = chunk
self._next_offset = 0
return self._current_fid
class ImageReceiverCAS5ANew(ImageReceiver):
# Documentation:
# https://twitter.com/scott23192/status/1630749478561935360
# https://mega.nz/file/4rIywT5L#WoZsMxzIkUKhqHTrYh__nvv_N9CGwVV-dLsJ2k4_2OA
def parse_chunk(self, chunk):
# The AX.25 header occupies 16 bytes
if len(chunk) <= 16:
return None
chunk = chunk[16:]
if not chunk.startswith(b'\x03'):
return None
return chunk
def chunk_sequence(self, chunk):
# sequences are 1-based rather than 0-based
return struct.unpack('>H', chunk[3:5])[0] - 1
def chunk_data(self, chunk):
return chunk[16:]
def chunk_size(self):
# This isn't stated explicitly in the documentation, but it seems that
# all the chunks except the last one are 240 bytes.
return 240
def is_last_chunk(self, chunk):
num_chunks = struct.unpack('>H', chunk[1:3])[0]
return num_chunks == self.chunk_sequence(chunk) + 1
cas5a = ImageReceiverCAS5A
cas5a_new = ImageReceiverCAS5ANew
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