Bluetooth Serial between Raspberry Pi 3 / Zero W and Arduino / HM-10 - serialization

Question

I am trying to establish a bluetooth serial communication link between a Raspberry Pi Zero W, running Raspbian Jessie [03-07-2017], and an Arduino (UNO).
I am currently able to write data to the Arduino using bluetoothctl.
The application requires that we are able to write data to a particular BLE Slave. There are multiple [HM-10] Slaves to switch between, the Slave needs to be chosen during the program execution.
There is no BAUD rate preference. Currently, we are using 9600 universally.
Functions have been created that automatically connect and then write data to an "attribute", this shows up as data on the Serial Monitor of the Arduino.
Python Code - using BlueZ 5.44 (manually installed):
import subprocess
from subprocess import Popen, PIPE
# Replaces the ':' with '_' to allow the MacAddress to be in the form
# of a "Path" when "selecting an attribute"
def changeMacAddr(word):
return ''.join(c if c != ':' else '_' for c in word)
# Connects to a given MacAddress and then selects the attribute to write to
def connBT(BTsubProcess, stringMacAddr):
BTsubProcess.stdin.write(bytes("".join("connect "+stringMacAddr +"\n"), "utf-8"))
BTsubProcess.stdin.flush()
time.sleep(2)
stringFormat = changeMacAddr(stringMacAddr)
BTsubProcess.stdin.write(bytes("".join("select-attribute /org/bluez/hci0/dev_"
+ stringFormat +
"/service0010/char0011" + "\n"), "utf-8"))
BTsubProcess.stdin.flush()
# Can only be run once connBT has run - writes the data in a list [must have numbers 0 - 255 ]
def writeBT(BTsubProcess, listOfData):
stringList = [str('{0} ').format(elem) for elem in listOfData]
BTsubProcess.stdin.write(bytes("".join("write " + "".join(stringList) + "\n"), "utf-8"))
BTsubProcess.stdin.flush()
# Disconnects
def clostBT(BTsubProcess):
BTsubProcess.communicate(bytes("disconnect\n", "utf-8"))
# To use the functions a subprocess "instance" of bluetoothctl must be made
blt = subprocess.Popen(["bluetoothctl"], stdin=subprocess.PIPE, shell=True)
# blt with then be passed into the function for BTsubProcess
# Note: the MacAddresses of the Bluetooth modules were pre-connected and trusted manually via bluetoothctl
This method works fine for small sets of data, but my requirements require me to stream data to the Arduino very quickly.
The current set up is:
Sensor data (accelerometer, EEG) via USB serial is received by the Pi
The Pi processes the data
Commands are then sent to the Arduino via the in built bluetooth of the Pi Zero W
However, while using this method the bluetooth data transmission would delay (temporarily freeze) when the sensor data changed.
The data transmission was flawless when using two pre-paired HM-10 modules, the Pi's GPIO serial port was configured using PySerial.
The following methods have also been tried:
Using WiringPi to set-up a bluetooth serial port on the /dev/ttyAMA0
using Python sockets and rfcomm
When attempting to use both of these methods. The Python code compiles, however, once the Serial Port is opened the data is seemingly not written and does not show up on the Arduino's Serial Monitor.
This then cripples the previous functions. Even when using bluetoothctl manually, the module cannot be unpaired/disconnected. Writing to the appropriate attribute does not work either.
A restart is required to regain normal function.
Is this approach correct?
Is there a better way to send data over BLE?
UPDATE: 05/07/2017
I am no longer working on this project. But troubleshooting has led me to believe that a "race condition" in the code may have led to the program not functioning as intended.
This was verified during the testing phase where a more barebones code was created that functioned very well.