Fun things for Dabeaz's superbad superboard

superboard.py

"""Fun things for Dabeaz's superbad superboard.
Default Audio Format:

    Frame rate: 48kHz
    Channels: 1
    Bytes per sample: 1

Superboard Encoding:

    Baud rate: 300
    Start bit: 0b0
    Stop bits: 0b11
    0: 4 square wave cycles at 1200 Hz
        40 samples (1 cycle) @ 48k Hz
        160 samples (4 cycles) @ 48 kHz (bit)
        1760 samples (44 cycles) @ 48 kHz (byte payload)
    1: 8 square wave cycles at 2400 Hz
        20 samples (1 cycle) @ 48 kHz
        160 samples (8 cycles) @ 48 kHz (bit)
        1760 samples (88 cycles) @ 48 kHz (byte payload)

Thoughts:
    * Why not use a slower sample rate (i.e. 2400 Hz)?
"""
import wave


def encode_bit(value, frame_rate=48000):
    cycles, frequency = ((4, 1200), (8, 2400))[value]
    data = bytearray()
    n_samples = frame_rate // frequency
    for i in range(n_samples // 2):
        data.append(0)
    for i in range(n_samples // 2):
        data.append(255)
    return cycles * data


def encode_byte(byte):
    data = bytearray(encode_bit(0))  # Start bit
    for bit in range(0, 8):
        if byte & 0x1:
            data.extend(encode_bit(1))
        else:
            data.extend(encode_bit(0))
        byte = byte >> 1
    data.extend(encode_bit(1) * 2)  # Stop bits
    return data


def encode_data(in_data):
    data = bytearray(encode_bit(1) * 1000)  # Padding
    for byte in in_data:
        data.extend(encode_byte(byte))
    data.extend(encode_bit(1) * 1000)   # Padding
    return data


def decode_samples(samples, frame_rate=48000):
    ref_samples = [encode_bit(n, frame_rate=frame_rate) for n in (0, 1)]
    bit_len = len(ref_samples[0])

    # Convert samples into bits
    bits = []
    for idx in range(0, len(samples), bit_len):
        bit = ref_samples.index(samples[idx:idx + bit_len])
        bits.append(bit)

    # Starting at first start bit, extract bytes from 11-bit chunks, skip
    # chunks with invalid start/stop bits
    data = bytearray()
    for idx in range(bits.index(0), len(bits), 11):
        bit_set = bits[idx:idx+11]
        if bit_set[0] != 0 or bit_set[-2:] != [1, 1]:
            continue
        value = 0
        for bit in bit_set[-3:0:-1]:
            value = (value << 1) | bit
        data.append(value)
    # data = data.replace(b'\n', b'\r\n')
    return data


def ascii_to_wav(in_file, out_file, frame_rate=48000, sample_width=1, channels=1):
    with open(in_file, "rb") as fh:
        in_data = fh.read()
    in_data = in_data.replace(b'\n', b'\r\n')
    data = encode_data(in_data)
    with wave.open(out_file, "wb") as w:
        w.setnchannels(channels)
        w.setsampwidth(sample_width)
        w.setframerate(frame_rate)
        w.writeframes(data)
    return data


def wav_to_ascii(in_file, out_file):
    with wave.open(in_file, "rb") as w:
        samples = w.readframes(w.getnframes())
        data = decode_samples(samples, w.getframerate())

    with open(out_file, "wb") as fh:
        fh.write(data)
    return data


assert decode_samples(encode_data(b'A')) == b'A'
assert decode_samples(encode_data(b'A')) == b'A'
ascii_to_wav("haiku_1_in.bas", "haiku_1_out.wav")
wav_to_ascii("haiku_1_out.wav", "haiku_1_out.bas")