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 """The encode module supports encoding HDLC frames."""
16 from pw_hdlc_lite import protocol
18 _ESCAPE_BYTE = bytes([protocol.ESCAPE])
19 _FLAG_BYTE = bytes([protocol.FLAG])
20 _CONTROL = 0 # Currently, hard-coded to 0; no sequence numbers are used
23 def information_frame(address: int, data: bytes) -> bytes:
24 """Encodes an HDLC I-frame with a CRC-32 frame check sequence."""
25 frame = bytearray([address, _CONTROL]) + data
26 frame += protocol.frame_check_sequence(frame)
27 frame = frame.replace(_ESCAPE_BYTE, b'\x7d\x5d')
28 frame = frame.replace(_FLAG_BYTE, b'\x7d\x5e')
29 return b''.join([_FLAG_BYTE, frame, _FLAG_BYTE])