"""
Core OpenBCI object for handling connections and samples from the Ganglion board.
Note that the LIB will take care on its own to print incoming ASCII messages if any (FIXME, BTW).
EXAMPLE USE:
def handle_sample(sample):
print(sample.channels_data)
board = OpenBCIBoard()
board.start(handle_sample)
TODO: support impedance
TODO: reset board with 'v'?
"""
from __future__ import print_function
import struct
import time
import timeit
import atexit
import logging
import numpy as np
import sys
import pdb
import glob
from bluepy.btle import Scanner, DefaultDelegate, Peripheral
SAMPLE_RATE = 200.0 # Hz
scale_fac_uVolts_per_count = 1200 / (8388607.0 * 1.5 * 51.0)
scale_fac_accel_G_per_count = 0.000016
# service for communication, as per docs
BLE_SERVICE = "fe84"
# characteristics of interest
BLE_CHAR_RECEIVE = "2d30c082f39f4ce6923f3484ea480596"
BLE_CHAR_SEND = "2d30c083f39f4ce6923f3484ea480596"
BLE_CHAR_DISCONNECT = "2d30c084f39f4ce6923f3484ea480596"
'''
#Commands for in SDK http://docs.openbci.com/Hardware/08-Ganglion_Data_Forma
command_stop = "s";
command_startBinary = "b";
'''
class OpenBCIGanglion(object):
"""
Handle a connection to an OpenBCI board.
Args:
port: MAC address of the Ganglion Board. "None" to attempt auto-detect.
aux: enable on not aux channels (i.e. switch to 18bit mode if set)
impedance: measures impedance when start streaming
timeout: in seconds, if set will try to disconnect / reconnect after a period without new data
-- should be high if impedance check
max_packets_to_skip: will try to disconnect / reconnect after too many packets are skipped
baud, filter_data, daisy: Not used, for compatibility with v3
"""
def __init__(self, port=None, baud=0, filter_data=False,
scaled_output=True, daisy=False, log=True, aux=False, impedance=False, timeout=2,
max_packets_to_skip=20):
# unused, for compatibility with Cyton v3 API
self.daisy = False
# these one are used
self.log = log # print_incoming_text needs log
self.aux = aux
self.streaming = False
self.timeout = timeout
self.max_packets_to_skip = max_packets_to_skip
self.scaling_output = scaled_output
self.impedance = impedance
# might be handy to know API
self.board_type = "ganglion"
print("Looking for Ganglion board")
if port == None:
port = self.find_port()
self.port = port # find_port might not return string
self.connect()
self.streaming = False
# number of EEG channels and (optionally) accelerometer channel
self.eeg_channels_per_sample = 4
self.aux_channels_per_sample = 3
self.imp_channels_per_sample = 5
self.read_state = 0
self.log_packet_count = 0
self.packets_dropped = 0
self.time_last_packet = 0
# Disconnects from board when terminated
atexit.register(self.disconnect)
def getBoardType(self):
""" Returns the version of the board """
return self.board_type
def setImpedance(self, flag):
""" Enable/disable impedance measure """
self.impedance = bool(flag)
def connect(self):
""" Connect to the board and configure it. Note: recreates various objects upon call. """
print("Init BLE connection with MAC: " + self.port)
print("NB: if it fails, try with root privileges.")
self.gang = Peripheral(self.port, 'random') # ADDR_TYPE_RANDOM
print("Get mainservice...")
self.service = self.gang.getServiceByUUID(BLE_SERVICE)
print("Got:" + str(self.service))
print("Get characteristics...")
self.char_read = self.service.getCharacteristics(BLE_CHAR_RECEIVE)[0]
print("receive, properties: " + str(self.char_read.propertiesToString()) +
", supports read: " + str(self.char_read.supportsRead()))
self.char_write = self.service.getCharacteristics(BLE_CHAR_SEND)[0]
print("write, properties: " + str(self.char_write.propertiesToString()) +
", supports read: " + str(self.char_write.supportsRead()))
self.char_discon = self.service.getCharacteristics(BLE_CHAR_DISCONNECT)[0]
print("disconnect, properties: " + str(self.char_discon.propertiesToString()) +
", supports read: " + str(self.char_discon.supportsRead()))
# set delegate to handle incoming data
self.delegate = GanglionDelegate(self.scaling_output)
self.gang.setDelegate(self.delegate)
# enable AUX channel
if self.aux:
print("Enabling AUX data...")
try:
self.ser_write(b'n')
except Exception as e:
print("Something went wrong while enabling aux channels: " + str(e))
print("Turn on notifications")
# nead up-to-date bluepy, cf https://github.com/IanHarvey/bluepy/issues/53
self.desc_notify = self.char_read.getDescriptors(forUUID=0x2902)[0]
try:
self.desc_notify.write(b"\x01")
except Exception as e:
print("Something went wrong while trying to enable notification: " + str(e))
print("Connection established")
def init_streaming(self):
""" Tell the board to record like crazy. """
try:
if self.impedance:
print("Starting with impedance testing")
self.ser_write(b'z')
else:
self.ser_write(b'b')
except Exception as e:
print("Something went wrong while asking the board to start streaming: " + str(e))
self.streaming = True
self.packets_dropped = 0
self.time_last_packet = timeit.default_timer()
def find_port(self):
"""Detects Ganglion board MAC address
If more than 1 around, will select first. Needs root privilege.
"""
print("Try to detect Ganglion MAC address. "
"NB: Turn on bluetooth and run as root for this to work!"
"Might not work with every BLE dongles.")
scan_time = 5
print("Scanning for 5 seconds nearby devices...")
# From bluepy example
class ScanDelegate(DefaultDelegate):
def __init__(self):
DefaultDelegate.__init__(self)
def handleDiscovery(self, dev, isNewDev, isNewData):
if isNewDev:
print("Discovered device: " + dev.addr)
elif isNewData:
print("Received new data from: " + dev.addr)
scanner = Scanner().withDelegate(ScanDelegate())
devices = scanner.scan(scan_time)
nb_devices = len(devices)
if nb_devices < 1:
print("No BLE devices found. Check connectivity.")
return ""
else:
print("Found " + str(nb_devices) + ", detecting Ganglion")
list_mac = []
list_id = []
for dev in devices:
# "Ganglion" should appear inside the "value" associated
# to "Complete Local Name", e.g. "Ganglion-b2a6"
for (adtype, desc, value) in dev.getScanData():
if desc == "Complete Local Name" and value.startswith("Ganglion"):
list_mac.append(dev.addr)
list_id.append(value)
print("Got Ganglion: " + value +
", with MAC: " + dev.addr)
break
nb_ganglions = len(list_mac)
if nb_ganglions < 1:
print("No Ganglion found ;(")
raise OSError('Cannot find OpenBCI Ganglion MAC address')
if nb_ganglions > 1:
print("Found " + str(nb_ganglions) + ", selecting first")
print("Selecting MAC address " + list_mac[0] + " for " + list_id[0])
return list_mac[0]
def ser_write(self, b):
"""Access serial port object for write"""
self.char_write.write(b)
def ser_read(self):
"""Access serial port object for read"""
return self.char_read.read()
def ser_inWaiting(self):
""" Slightly different from Cyton API, return True if ASCII messages are incoming."""
# FIXME: might have a slight problem with thread because of notifications...
if self.delegate.receiving_ASCII:
# in case the packet indicating the end of the message drops, we use a 1s timeout
if timeit.default_timer() - self.delegate.time_last_ASCII > 2:
self.delegate.receiving_ASCII = False
return self.delegate.receiving_ASCII
def getSampleRate(self):
return SAMPLE_RATE
def getNbEEGChannels(self):
"""Will not get new data on impedance check."""
return self.eeg_channels_per_sample
def getNbAUXChannels(self):
"""Might not be used depending on the mode."""
return self.aux_channels_per_sample
def getNbImpChannels(self):
"""Might not be used depending on the mode."""
return self.imp_channels_per_sample
def start_streaming(self, callback, lapse=-1):
"""
Start handling streaming data from the board. Call a provided callback
for every single sample that is processed
Args:
callback: A callback function or a list of functions that will receive a single argument
of the OpenBCISample object captured.
"""
if not self.streaming:
self.init_streaming()
start_time = timeit.default_timer()
# Enclose callback funtion in a list if it comes alone
if not isinstance(callback, list):
callback = [callback]
while self.streaming:
# should the board get disconnected and we could not wait for notification
# anymore, a reco should be attempted through timeout mechanism
try:
# at most we will get one sample per packet
self.waitForNotifications(1. / self.getSampleRate())
except Exception as e:
print("Something went wrong while waiting for a new sample: " + str(e))
# retrieve current samples on the stack
samples = self.delegate.getSamples()
self.packets_dropped = self.delegate.getMaxPacketsDropped()
if samples:
self.time_last_packet = timeit.default_timer()
for call in callback:
for sample in samples:
call(sample)
if (lapse > 0 and timeit.default_timer() - start_time > lapse):
self.stop()
if self.log:
self.log_packet_count = self.log_packet_count + 1
# Checking connection -- timeout and packets dropped
self.check_connection()
def waitForNotifications(self, delay):
""" Allow some time for the board to receive new data. """
self.gang.waitForNotifications(delay)
def test_signal(self, signal):
""" Enable / disable test signal """
if signal == 0:
self.warn("Disabling synthetic square wave")
try:
self.char_write.write(b']')
except Exception as e:
print("Something went wrong while setting signal: " + str(e))
elif signal == 1:
self.warn("Eisabling synthetic square wave")
try:
self.char_write.write(b'[')
except Exception as e:
print("Something went wrong while setting signal: " + str(e))
else:
self.warn(
"%s is not a known test signal. Valid signal is 0-1" % signal)
def set_channel(self, channel, toggle_position):
""" Enable / disable channels """
try:
# Commands to set toggle to on position
if toggle_position == 1:
if channel is 1:
self.ser.write(b'!')
if channel is 2:
self.ser.write(b'@')
if channel is 3:
self.ser.write(b'#')
if channel is 4:
self.ser.write(b'$')
# Commands to set toggle to off position
elif toggle_position == 0:
if channel is 1:
self.ser.write(b'1')
if channel is 2:
self.ser.write(b'2')
if channel is 3:
self.ser.write(b'3')
if channel is 4:
self.ser.write(b'4')
except Exception as e:
print("Something went wrong while setting channels: " + str(e))
"""
Clean Up (atexit)
"""
def stop(self):
print("Stopping streaming...")
self.streaming = False
# connection might be already down here
try:
if self.impedance:
print("Stopping with impedance testing")
self.ser_write(b'Z')
else:
self.ser_write(b's')
except Exception as e:
print("Something went wrong while asking the board to stop streaming: " + str(e))
if self.log:
logging.warning('sent <s>: stopped streaming')
def disconnect(self):
if (self.streaming == True):
self.stop()
print("Closing BLE..")
try:
self.char_discon.write(b' ')
except Exception as e:
print("Something went wrong while asking the board to disconnect: " + str(e))
# should not try to read/write anything after that, will crash
try:
self.gang.disconnect()
except Exception as e:
print("Something went wrong while shutting down BLE link: " + str(e))
logging.warning('BLE closed')
"""
SETTINGS AND HELPERS
"""
def warn(self, text):
if self.log:
# log how many packets where sent succesfully in between warnings
if self.log_packet_count:
logging.info('Data packets received:' +
str(self.log_packet_count))
self.log_packet_count = 0
logging.warning(text)
print("Warning: %s" % text)
def check_connection(self):
""" Check connection quality in term of lag and number of packets drop.
Reinit connection if necessary.
FIXME: parameters given to the board will be lost.
"""
# stop checking when we're no longer streaming
if not self.streaming:
return
# check number of dropped packets and duration without new packets, deco/reco if too large
if self.packets_dropped > self.max_packets_to_skip:
self.warn("Too many packets dropped, attempt to reconnect")
self.reconnect()
elif self.timeout > 0 and timeit.default_timer() - self.time_last_packet > self.timeout:
self.warn("Too long since got new data, attempt to reconnect")
# if error, attempt to reconect
self.reconnect()
def reconnect(self):
""" In case of poor connection, will shut down and relaunch everything.
FIXME: parameters given to the board will be lost."""
self.warn('Reconnecting')
self.stop()
self.disconnect()
self.connect()
self.init_streaming()
class OpenBCISample(object):
"""Object encapsulating a single sample from the OpenBCI board."""
def __init__(self, packet_id, channel_data, aux_data, imp_data):
self.id = packet_id
self.channel_data = channel_data
self.aux_data = aux_data
self.imp_data = imp_data
class GanglionDelegate(DefaultDelegate):
""" Called by bluepy (handling BLE connection) when new data arrive, parses samples. """
def __init__(self, scaling_output=True):
DefaultDelegate.__init__(self)
# holds samples until OpenBCIBoard claims them
self.samples = []
# detect gaps between packets
self.last_id = -1
self.packets_dropped = 0
# save uncompressed data to compute deltas
self.lastChannelData = [0, 0, 0, 0]
# 18bit data got here and then accelerometer with it
self.lastAcceleromoter = [0, 0, 0]
# when the board is manually set in the right mode (z to start, Z to stop)
# impedance will be measured. 4 channels + ref
self.lastImpedance = [0, 0, 0, 0, 0]
self.scaling_output = scaling_output
# handling incoming ASCII messages
self.receiving_ASCII = False
self.time_last_ASCII = timeit.default_timer()
def handleNotification(self, cHandle, data):
if len(data) < 1:
print('Warning: a packet should at least hold one byte...')
return
self.parse(data)
"""
PARSER:
Parses incoming data packet into OpenBCISample -- see docs.
Will call the corresponding parse* function depending on the format of the packet.
"""
def parse(self, packet):
# bluepy returns INT with python3 and STR with python2
if type(packet) is str:
# convert a list of strings in bytes
unpac = struct.unpack(str(len(packet)) + 'B', "".join(packet))
else:
unpac = packet
start_byte = unpac[0]
# Give the informative part of the packet to proper handler
# split between ID and data bytes
# Raw uncompressed
if start_byte == 0:
self.receiving_ASCII = False
self.parseRaw(start_byte, unpac[1:])
# 18-bit compression with Accelerometer
elif start_byte >= 1 and start_byte <= 100:
self.receiving_ASCII = False
self.parse18bit(start_byte, unpac[1:])
# 19-bit compression without Accelerometer
elif start_byte >= 101 and start_byte <= 200:
self.receiving_ASCII = False
self.parse19bit(start_byte - 100, unpac[1:])
# Impedance Channel
elif start_byte >= 201 and start_byte <= 205:
self.receiving_ASCII = False
self.parseImpedance(start_byte, packet[1:])
# Part of ASCII -- TODO: better formatting of incoming ASCII
elif start_byte == 206:
print("%\t" + str(packet[1:]))
self.receiving_ASCII = True
self.time_last_ASCII = timeit.default_timer()
# End of ASCII message
elif start_byte == 207:
print("%\t" + str(packet[1:]))
print("$$$")
self.receiving_ASCII = False
else:
print("Warning: unknown type of packet: " + str(start_byte))
def parseRaw(self, packet_id, packet):
""" Dealing with "Raw uncompressed" """
if len(packet) != 19:
print('Wrong size, for raw data' +
str(len(packet)) + ' instead of 19 bytes')
return
chan_data = []
# 4 channels of 24bits, take values one by one
for i in range(0, 12, 3):
chan_data.append(conv24bitsToInt(packet[i:i + 3]))
# save uncompressed raw channel for future use and append whole sample
self.pushSample(packet_id, chan_data,
self.lastAcceleromoter, self.lastImpedance)
self.lastChannelData = chan_data
self.updatePacketsCount(packet_id)
def parse19bit(self, packet_id, packet):
""" Dealing with "19-bit compression without Accelerometer" """
if len(packet) != 19:
print('Wrong size, for 19-bit compression data' +
str(len(packet)) + ' instead of 19 bytes')
return
# should get 2 by 4 arrays of uncompressed data
deltas = decompressDeltas19Bit(packet)
# the sample_id will be shifted
delta_id = 1
for delta in deltas:
# convert from packet to sample id
sample_id = (packet_id - 1) * 2 + delta_id
# 19bit packets hold deltas between two samples
# TODO: use more broadly numpy
full_data = list(np.array(self.lastChannelData) - np.array(delta))
# NB: aux data updated only in 18bit mode, send values here only to be consistent
self.pushSample(sample_id, full_data,
self.lastAcceleromoter, self.lastImpedance)
self.lastChannelData = full_data
delta_id += 1
self.updatePacketsCount(packet_id)
def parse18bit(self, packet_id, packet):
""" Dealing with "18-bit compression without Accelerometer" """
if len(packet) != 19:
print('Wrong size, for 18-bit compression data' +
str(len(packet)) + ' instead of 19 bytes')
return
# accelerometer X
if packet_id % 10 == 1:
self.lastAcceleromoter[0] = conv8bitToInt8(packet[18])
# accelerometer Y
elif packet_id % 10 == 2:
self.lastAcceleromoter[1] = conv8bitToInt8(packet[18])
# accelerometer Z
elif packet_id % 10 == 3:
self.lastAcceleromoter[2] = conv8bitToInt8(packet[18])
# deltas: should get 2 by 4 arrays of uncompressed data
deltas = decompressDeltas18Bit(packet[:-1])
# the sample_id will be shifted
delta_id = 1
for delta in deltas:
# convert from packet to sample id
sample_id = (packet_id - 1) * 2 + delta_id
# 19bit packets hold deltas between two samples
# TODO: use more broadly numpy
full_data = list(np.array(self.lastChannelData) - np.array(delta))
self.pushSample(sample_id, full_data,
self.lastAcceleromoter, self.lastImpedance)
self.lastChannelData = full_data
delta_id += 1
self.updatePacketsCount(packet_id)
def parseImpedance(self, packet_id, packet):
""" Dealing with impedance data. packet: ASCII data.
NB: will take few packet (seconds) to fill
"""
if packet[-2:] != b"Z\n":
print('Wrong format for impedance check, should be ASCII ending with "Z\\n"')
# convert from ASCII to actual value
imp_value = int(packet[:-2]) / 2
# from 201 to 205 codes to the right array size
self.lastImpedance[packet_id - 201] = imp_value
self.pushSample(packet_id - 200, self.lastChannelData,
self.lastAcceleromoter, self.lastImpedance)
def pushSample(self, sample_id, chan_data, aux_data, imp_data):
""" Add a sample to inner stack, setting ID and dealing with scaling if necessary. """
if self.scaling_output:
chan_data = list(np.array(chan_data) * scale_fac_uVolts_per_count)
aux_data = list(np.array(aux_data) * scale_fac_accel_G_per_count)
sample = OpenBCISample(sample_id, chan_data, aux_data, imp_data)
self.samples.append(sample)
def updatePacketsCount(self, packet_id):
"""Update last packet ID and dropped packets"""
if self.last_id == -1:
self.last_id = packet_id
self.packets_dropped = 0
return
# ID loops every 101 packets
if packet_id > self.last_id:
self.packets_dropped = packet_id - self.last_id - 1
else:
self.packets_dropped = packet_id + 101 - self.last_id - 1
self.last_id = packet_id
if self.packets_dropped > 0:
print("Warning: dropped " + str(self.packets_dropped) + " packets.")
def getSamples(self):
""" Retrieve and remove from buffer last samples. """
unstack_samples = self.samples
self.samples = []
return unstack_samples
def getMaxPacketsDropped(self):
""" While processing last samples, how many packets were dropped?"""
# TODO: return max value of the last samples array?
return self.packets_dropped
"""
DATA conversion, for the most part courtesy of OpenBCI_NodeJS_Ganglion
"""
def conv24bitsToInt(unpacked):
""" Convert 24bit data coded on 3 bytes to a proper integer """
if len(unpacked) != 3:
raise ValueError("Input should be 3 bytes long.")
# FIXME: quick'n dirty, unpack wants strings later on
literal_read = struct.pack('3B', unpacked[0], unpacked[1], unpacked[2])
# 3byte int in 2s compliment
if (unpacked[0] > 127):
pre_fix = bytes(bytearray.fromhex('FF'))
else:
pre_fix = bytes(bytearray.fromhex('00'))
literal_read = pre_fix + literal_read
# unpack little endian(>) signed integer(i) (makes unpacking platform independent)
myInt = struct.unpack('>i', literal_read)[0]
return myInt
def conv19bitToInt32(threeByteBuffer):
""" Convert 19bit data coded on 3 bytes to a proper integer (LSB bit 1 used as sign). """
if len(threeByteBuffer) != 3:
raise ValueError("Input should be 3 bytes long.")
prefix = 0
# if LSB is 1, negative number, some hasty unsigned to signed conversion to do
if threeByteBuffer[2] & 0x01 > 0:
prefix = 0b1111111111111
return ((prefix << 19) | (threeByteBuffer[0] << 16) |
(threeByteBuffer[1] << 8) | threeByteBuffer[2]) | ~0xFFFFFFFF
else:
return (prefix << 19) | (threeByteBuffer[0] << 16) |\
(threeByteBuffer[1] << 8) | threeByteBuffer[2]
def conv18bitToInt32(threeByteBuffer):
""" Convert 18bit data coded on 3 bytes to a proper integer (LSB bit 1 used as sign) """
if len(threeByteBuffer) != 3:
raise ValueError("Input should be 3 bytes long.")
prefix = 0
# if LSB is 1, negative number, some hasty unsigned to signed conversion to do
if threeByteBuffer[2] & 0x01 > 0:
prefix = 0b11111111111111
return ((prefix << 18) | (threeByteBuffer[0] << 16) |
(threeByteBuffer[1] << 8) | threeByteBuffer[2]) | ~0xFFFFFFFF
else:
return (prefix << 18) | (threeByteBuffer[0] << 16) |\
(threeByteBuffer[1] << 8) | threeByteBuffer[2]
def conv8bitToInt8(byte):
""" Convert one byte to signed value """
if byte > 127:
return (256 - byte) * (-1)
else:
return byte
def decompressDeltas19Bit(buffer):
"""
Called to when a compressed packet is received.
buffer: Just the data portion of the sample. So 19 bytes.
return {Array} - An array of deltas of shape 2x4
(2 samples per packet and 4 channels per sample.)
"""
if len(buffer) != 19:
raise ValueError("Input should be 19 bytes long.")
receivedDeltas = [[0, 0, 0, 0], [0, 0, 0, 0]]
# Sample 1 - Channel 1
miniBuf = [
(buffer[0] >> 5),
((buffer[0] & 0x1F) << 3 & 0xFF) | (buffer[1] >> 5),
((buffer[1] & 0x1F) << 3 & 0xFF) | (buffer[2] >> 5)
]
receivedDeltas[0][0] = conv19bitToInt32(miniBuf)
# Sample 1 - Channel 2
miniBuf = [
(buffer[2] & 0x1F) >> 2,
(buffer[2] << 6 & 0xFF) | (buffer[3] >> 2),
(buffer[3] << 6 & 0xFF) | (buffer[4] >> 2)
]
receivedDeltas[0][1] = conv19bitToInt32(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)
]
receivedDeltas[0][2] = conv19bitToInt32(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)
]
receivedDeltas[0][3] = conv19bitToInt32(miniBuf)
# Sample 2 - Channel 1
miniBuf = [
((buffer[9] & 0x0F) >> 1),
(buffer[9] << 7 & 0xFF) | (buffer[10] >> 1),
(buffer[10] << 7 & 0xFF) | (buffer[11] >> 1)
]
receivedDeltas[1][0] = conv19bitToInt32(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)
]
receivedDeltas[1][1] = conv19bitToInt32(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)
]
receivedDeltas[1][2] = conv19bitToInt32(miniBuf)
# Sample 2 - Channel 4
miniBuf = [(buffer[16] & 0x07), buffer[17], buffer[18]]
receivedDeltas[1][3] = conv19bitToInt32(miniBuf)
return receivedDeltas
def decompressDeltas18Bit(buffer):
"""
Called to when a compressed packet is received.
buffer: Just the data portion of the sample. So 19 bytes.
return {Array} - An array of deltas of shape 2x4
(2 samples per packet and 4 channels per sample.)
"""
if len(buffer) != 18:
raise ValueError("Input should be 18 bytes long.")
receivedDeltas = [[0, 0, 0, 0], [0, 0, 0, 0]]
# Sample 1 - Channel 1
miniBuf = [
(buffer[0] >> 6),
((buffer[0] & 0x3F) << 2 & 0xFF) | (buffer[1] >> 6),
((buffer[1] & 0x3F) << 2 & 0xFF) | (buffer[2] >> 6)
]
receivedDeltas[0][0] = conv18bitToInt32(miniBuf)
# Sample 1 - Channel 2
miniBuf = [
(buffer[2] & 0x3F) >> 4,
(buffer[2] << 4 & 0xFF) | (buffer[3] >> 4),
(buffer[3] << 4 & 0xFF) | (buffer[4] >> 4)
]
receivedDeltas[0][1] = conv18bitToInt32(miniBuf)
# Sample 1 - Channel 3
miniBuf = [
(buffer[4] & 0x0F) >> 2,
(buffer[4] << 6 & 0xFF) | (buffer[5] >> 2),
(buffer[5] << 6 & 0xFF) | (buffer[6] >> 2)
]
receivedDeltas[0][2] = conv18bitToInt32(miniBuf)
# Sample 1 - Channel 4
miniBuf = [
(buffer[6] & 0x03),
buffer[7],
buffer[8]
]
receivedDeltas[0][3] = conv18bitToInt32(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)
]
receivedDeltas[1][0] = conv18bitToInt32(miniBuf)
# Sample 2 - Channel 2
miniBuf = [
(buffer[11] & 0x3F) >> 4,
(buffer[11] << 4 & 0xFF) | (buffer[12] >> 4),
(buffer[12] << 4 & 0xFF) | (buffer[13] >> 4)
]
receivedDeltas[1][1] = conv18bitToInt32(miniBuf)
# Sample 2 - Channel 3
miniBuf = [
(buffer[13] & 0x0F) >> 2,
(buffer[13] << 6 & 0xFF) | (buffer[14] >> 2),
(buffer[14] << 6 & 0xFF) | (buffer[15] >> 2)
]
receivedDeltas[1][2] = conv18bitToInt32(miniBuf)
# Sample 2 - Channel 4
miniBuf = [
(buffer[15] & 0x03),
buffer[16],
buffer[17]
]
receivedDeltas[1][3] = conv18bitToInt32(miniBuf)
return receivedDeltas
