1 # Copyright 2020 The Pigweed Authors
3 # Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 # use this file except in compliance with the License. You may obtain a copy of
7 # https://www.apache.org/licenses/LICENSE-2.0
9 # Unless required by applicable law or agreed to in writing, software
10 # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 # License for the specific language governing permissions and limitations under
14 """Module for low-level HDLC protocol features."""
18 # Special flag character for delimiting HDLC frames.
21 # Special character for escaping other special characters in a frame.
24 # Characters allowed after a 0x7d escape character.
25 VALID_ESCAPED_BYTES = 0x5D, 0x5E
28 def escape(byte: int) -> int:
29 """Escapes or unescapes a byte, which should have been preceeded by 0x7d."""
33 def frame_check_sequence(data: bytes) -> bytes:
34 return zlib.crc32(data).to_bytes(4, 'little')
38 def __init__(self, frame_type: int):
39 self._data: bytes = bytes([0x03 | frame_type])
46 def unnumbered_information(cls):
47 return UFrameControl(0x00)