def _parse_compressed_19bit(self, packet_id, packet):
"""Parse a 19-bit compressed packet without accelerometer data."""
if bad_data_size(packet, 19, "19-bit compressed data"):
return
packet_id -= 100
# should get 2 by 4 arrays of uncompressed data
deltas = decompress_deltas_19bit(packet)
self._update_data_with_deltas(packet_id, deltas)
def _parse_uncompressed(self, packet_id, packet):
"""Parse a raw uncompressed packet."""
if bad_data_size(packet, 19, "uncompressed data"):
return
# 4 channels of 24bits
self._last_eeg_data[:] = [
int_from_24bits(packet[i:i + 3]) for i in range(0, 12, 3)
]
# = np.array([chan_data], dtype=np.float32).T
self._update_counts_and_enqueue("EEG", packet_id)
def decompress_deltas_19bit(buffer):
"""Parse packet deltas from 19-bit compression format."""
if bad_data_size(buffer, 19, "19-byte compressed packet"):
raise ValueError("Bad input size for byte conversion.")
deltas = np.zeros((2, 4))
# Sample 1 - Channel 1
minibuf = [(buffer[0] >> 5),
((buffer[0] & 0x1F) << 3 & 0xFF) | (buffer[1] >> 5),
((buffer[1] & 0x1F) << 3 & 0xFF) | (buffer[2] >> 5)]
deltas[0][0] = int32_from_19bit(minibuf)
# Sample 1 - Channel 2
minibuf = [(buffer[2] & 0x1F) >> 2,
(buffer[2] << 6 & 0xFF) | (buffer[3] >> 2),
(buffer[3] << 6 & 0xFF) | (buffer[4] >> 2)]
deltas[0][1] = int32_from_19bit(minibuf)
# Sample 1 - Channel 3
minibuf = [((buffer[4] & 0x03) << 1 & 0xFF) | (buffer[5] >> 7),
((buffer[5] & 0x7F) << 1 & 0xFF) | (buffer[6] >> 7),
((buffer[6] & 0x7F) << 1 & 0xFF) | (buffer[7] >> 7)]
deltas[0][2] = int32_from_19bit(minibuf)
# Sample 1 - Channel 4
minibuf = [((buffer[7] & 0x7F) >> 4),
((buffer[7] & 0x0F) << 4 & 0xFF) | (buffer[8] >> 4),
((buffer[8] & 0x0F) << 4 & 0xFF) | (buffer[9] >> 4)]
deltas[0][3] = int32_from_19bit(minibuf)
# Sample 2 - Channel 1
minibuf = [((buffer[9] & 0x0F) >> 1),
(buffer[9] << 7 & 0xFF) | (buffer[10] >> 1),
(buffer[10] << 7 & 0xFF) | (buffer[11] >> 1)]
deltas[1][0] = int32_from_19bit(minibuf)
# Sample 2 - Channel 2
minibuf = [((buffer[11] & 0x01) << 2 & 0xFF) | (buffer[12] >> 6),
(buffer[12] << 2 & 0xFF) | (buffer[13] >> 6),
(buffer[13] << 2 & 0xFF) | (buffer[14] >> 6)]
deltas[1][1] = int32_from_19bit(minibuf)
# Sample 2 - Channel 3
minibuf = [((buffer[14] & 0x38) >> 3),
((buffer[14] & 0x07) << 5 & 0xFF) | ((buffer[15] & 0xF8) >> 3),
((buffer[15] & 0x07) << 5 & 0xFF) | ((buffer[16] & 0xF8) >> 3)]
deltas[1][2] = int32_from_19bit(minibuf)
# Sample 2 - Channel 4
minibuf = [(buffer[16] & 0x07), buffer[17], buffer[18]]
deltas[1][3] = int32_from_19bit(minibuf)
return deltas
def int_from_24bits(unpacked):
"""Convert 24-bit data coded on 3 bytes to a proper integer."""
if bad_data_size(unpacked, 3, "3-byte buffer"):
raise ValueError("Bad input size for byte conversion.")
# FIXME: quick'n dirty, unpack wants strings later on
int_bytes = INT_SIGN_BYTE[unpacked[0] > 127] + struct.pack('3B', *unpacked)
# unpack little endian(>) signed integer(i) (-> platform independent)
int_unpacked = struct.unpack('>i', int_bytes)[0]
return int_unpacked
def decompress_deltas_18bit(buffer):
"""Parse packet deltas from 18-byte compression format."""
if bad_data_size(buffer, 18, "18-byte compressed packet"):
raise ValueError("Bad input size for byte conversion.")
deltas = np.zeros((2, 4))
# Sample 1 - Channel 1
minibuf = [(buffer[0] >> 6),
((buffer[0] & 0x3F) << 2 & 0xFF) | (buffer[1] >> 6),
((buffer[1] & 0x3F) << 2 & 0xFF) | (buffer[2] >> 6)]
deltas[0][0] = int32_from_18bit(minibuf)
# Sample 1 - Channel 2
minibuf = [(buffer[2] & 0x3F) >> 4,
(buffer[2] << 4 & 0xFF) | (buffer[3] >> 4),
(buffer[3] << 4 & 0xFF) | (buffer[4] >> 4)]
deltas[0][1] = int32_from_18bit(minibuf)
# Sample 1 - Channel 3
minibuf = [(buffer[4] & 0x0F) >> 2,
(buffer[4] << 6 & 0xFF) | (buffer[5] >> 2),
(buffer[5] << 6 & 0xFF) | (buffer[6] >> 2)]
deltas[0][2] = int32_from_18bit(minibuf)
# Sample 1 - Channel 4
minibuf = [(buffer[6] & 0x03), buffer[7], buffer[8]]
deltas[0][3] = int32_from_18bit(minibuf)
# Sample 2 - Channel 1
minibuf = [(buffer[9] >> 6),
((buffer[9] & 0x3F) << 2 & 0xFF) | (buffer[10] >> 6),
((buffer[10] & 0x3F) << 2 & 0xFF) | (buffer[11] >> 6)]
deltas[1][0] = int32_from_18bit(minibuf)
# Sample 2 - Channel 2
minibuf = [(buffer[11] & 0x3F) >> 4,
(buffer[11] << 4 & 0xFF) | (buffer[12] >> 4),
(buffer[12] << 4 & 0xFF) | (buffer[13] >> 4)]
deltas[1][1] = int32_from_18bit(minibuf)
# Sample 2 - Channel 3
minibuf = [(buffer[13] & 0x0F) >> 2,
(buffer[13] << 6 & 0xFF) | (buffer[14] >> 2),
(buffer[14] << 6 & 0xFF) | (buffer[15] >> 2)]
deltas[1][2] = int32_from_18bit(minibuf)
# Sample 2 - Channel 4
minibuf = [(buffer[15] & 0x03), buffer[16], buffer[17]]
deltas[1][3] = int32_from_18bit(minibuf)
return deltas
def int32_from_18bit(three_byte_buffer):
"""Convert 18-bit data coded on 3 bytes to a proper integer."""
if bad_data_size(three_byte_buffer, 3, "3-byte buffer"):
raise ValueError("Bad input size for byte conversion.")
# if LSB is 1, negative number, some hasty unsigned to signed conversion to do
if three_byte_buffer[2] & 0x01 > 0:
prefix = 0b11111111111111
int32 = ((prefix << 18) | (three_byte_buffer[0] << 16)
| (three_byte_buffer[1] << 8) | three_byte_buffer[2]) \
| ~0xFFFFFFFF
else:
prefix = 0
int32 = (prefix << 18) | (three_byte_buffer[0] << 16) \
| (three_byte_buffer[1] << 8) | three_byte_buffer[2]
return int32
def _parse_compressed_18bit(self, packet_id, packet):
""" Dealing with "18-bit compression without Accelerometer" """
if bad_data_size(packet, 19, "18-bit compressed data"):
return
# set appropriate accelerometer byte
id_ones = packet_id % 10 - 1
if id_ones in [0, 1, 2]:
value = int8_from_byte(packet[18])
self._chunks["accelerometer"][0, id_ones] = value
if id_ones == 2:
self._update_counts_and_enqueue("accelerometer",
packet_id // 10)
# deltas: should get 2 by 4 arrays of uncompressed data
deltas = decompress_deltas_18bit(packet[:-1])
self._update_data_with_deltas(packet_id, deltas)