1# Copyright 2020 The Pigweed Authors
2#
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
5# the License at
6#
7#     https://www.apache.org/licenses/LICENSE-2.0
8#
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
13# the License.
14"""The encode module supports encoding HDLC frames."""
15
16from pw_hdlc import protocol
17
18_ESCAPE_BYTE = bytes([protocol.ESCAPE])
19_FLAG_BYTE = bytes([protocol.FLAG])
20
21
22def ui_frame(address: int, data: bytes) -> bytes:
23    """Encodes an HDLC UI-frame with a CRC-32 frame check sequence."""
24    frame = protocol.encode_address(
25        address) + protocol.UFrameControl.unnumbered_information().data + 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])
30