blob: cd2621fb8ac790df8d377d5156fd1a410068938f (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
"""
Bell 202 frequency-toggle line code (1200 baud AFSK layer).
On-air rule: bit 0 → toggle mark/space tone; bit 1 → hold current tone.
We avoid the legacy term in API names — this is Bell 202 / amateur packet radio.
"""
from __future__ import annotations
MARK_HZ = 1200.0
SPACE_HZ = 2200.0
BAUD_1200 = 1200
TONE_MARK = 1
TONE_SPACE = 0
def encode_bits_to_tones(bits: bytes, start_tone: int = TONE_SPACE) -> list[int]:
"""Map HDLC bit stream to mark/space tone sequence (one tone per bit)."""
tone = start_tone
out: list[int] = []
for byte in bits:
for bit_i in range(7, -1, -1):
bit = (byte >> bit_i) & 1
if bit == 0:
tone ^= 1
out.append(tone)
return out
def decode_tones_to_bits(tones: list[int], start_tone: int = TONE_SPACE) -> bytes:
"""Recover bit stream from mark/space tone sequence."""
if not tones:
return b""
prev = start_tone
bits: list[int] = []
for tone in tones:
if tone not in (TONE_MARK, TONE_SPACE):
continue
bits.append(0 if tone != prev else 1)
prev = tone
buf = bytearray()
for i in range(0, len(bits), 8):
chunk = bits[i : i + 8]
if len(chunk) < 8:
break
val = 0
for b in chunk:
val = (val << 1) | b
buf.append(val)
return bytes(buf)
|
