I have a bluetooth connection between a Raspberry Pi 3b+ and an Arduino Mega, using the RPi built-in module, and an HC-05 module on the Arduino. Bi-directional communication works like a charm, for minutes to sometimes, hours at a time.
Then, at seemingly random times, the python code hangs, blocked on the sock.recv() function. I can kill it via ctrl-c, and restart it, and it usually reconnects without a problem.
I know Bluetooth is a little finicky and so while any suggestions of how to make the communication more robust and extend the runtime-until-hanging are definitely appreciated, what I'm more interested in is how to detect this "hanging" and recover from it. i.e.: I want to just kill the connection and try to reconnect from within the Python program, rather than me having to see this myself and react to it.
This is what I have so far in python:
#!/usr/bin/python3
import datetime
import socket
import sys
import time
import bluetooth
COMMAND_START_CHAR = '<'
COMMAND_END_CHAR = '>'
LOGFILE = 'bt.log'
def SearchForFullCommand(buffer):
"""Puts fully formed commands from buffer into a list, returning the remaining buffer.
We expect commands to be demarcated by COMMAND_START_CHAR and COMMAND_END_CHAR. The
buffer may have zero or more such commands. This function finds all demarcated commands,
strips off those demarcations, and returns the remaining buffer. Any text that arrives
before a COMMAND_START_CHAR is discarded.
Args:
buffer: string representing the text received so far.
Returns:
A 2-tuple, where the first element is the remaining buffer, and the second element
is a potentially empty list of identified commands.
"""
commands = []
while COMMAND_END_CHAR in buffer:
end_pos = buffer.find(COMMAND_END_CHAR)
if COMMAND_START_CHAR in buffer[:end_pos]:
start_pos = buffer.find(COMMAND_START_CHAR) + len(COMMAND_START_CHAR)
commands.append(buffer[start_pos:end_pos])
buffer = buffer[end_pos+len(COMMAND_END_CHAR):]
return (buffer, commands) # no command found
def Log(s):
"""Appends message s to the logfile."""
with open(LOGFILE, 'a') as f:
f.write('%s\n' % s)
def ConnectBluetooth(address, port):
"""Attempts to make one connection to the given address and port."""
sock = bluetooth.BluetoothSocket(bluetooth.RFCOMM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
try:
sock.connect((address, port))
except (bluetooth.btcommon.BluetoothError) as e:
Log('Failed to connect: %s' % e)
return None
return sock
def ConnectBluetoothRetry(address, port, seconds):
"""Attempts to make connections for a number of seconds, exiting program on fail."""
second = 0
while second < seconds:
sock = ConnectBluetooth(address, port)
if sock:
Log('Connected after %d seconds' % second)
return sock
time.sleep(1)
second += 1
Log('Failed to connect after %d seconds' % second)
sys.exit()
def main():
"""Sends sequential numbers over bluetooth, and receives & parses anything sent."""
sys.stderr = open(LOGFILE, 'a')
start = time.time()
timestring = datetime.datetime.fromtimestamp(start).strftime('%Y-%m-%d %H:%M:%S')
Log('Started at %s' % timestring)
bd_addr = '98:D3:11:FC:42:16'
port = 1
sock = ConnectBluetoothRetry(bd_addr, port, 10)
buffer = ''
x = 0
while True:
try:
recv = sock.recv(1024)
except (bluetooth.btcommon.BluetoothError) as e:
Log('Failed to receive: %s' % e)
sock.close()
sock = ConnectBluetoothRetry(bd_addr, port, 10)
Log('.. %s (len=%d) after running for %.3f hours' % (
recv, len(recv), (time.time() - start) / 60**2))
buffer += recv.decode()
buffer, commands = SearchForFullCommand(buffer)
if commands:
for n, command in enumerate(commands):
Log('Received full command #%d: %s' % (n, command))
send = COMMAND_START_CHAR+str(x)+COMMAND_END_CHAR
try:
sock.send(send)
except (bluetooth.btcommon.BluetoothError) as e:
Log('Failed to send %s: %s' % (send, e))
sock.close()
sock = ConnectBluetoothRetry(bd_addr, port, 10)
Log('Sent %s' % send)
x += 1
time.sleep(1)
main()
When working well, the python log file looks like this:
.. b'646>' (len=4) after running for 0.843 hours
Received full command #0: 646
Sent <2526>
.. b'<647>' (len=5) after running for 0.843 hours
Received full command #0: 647
Sent <2527>
.. b'<' (len=1) after running for 0.844 hours
Sent <2528>
.. b'648>' (len=4) after running for 0.844 hours
Then, noticing it had stopped working, I killed it, and then restarted it:
KeyboardInterrupt
Started at 2020-05-03 11:15:07
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect: [Errno 16] Device or resource busy
Failed to connect after 10 seconds
I try again:
Started at 2020-05-03 11:15:42
Failed to connect: [Errno 112] Host is down
Failed to connect: [Errno 112] Host is down
Failed to connect: [Errno 112] Host is down
Connected after 3 seconds
.. b'1146><1147><1148><1149><1150><1151><1152><1153><1154><1155><1156><1157><1158><1159><1160><1161><1162><1163><1164><1165><1166><1' (len=127) after running for 0.005 hours
Received full command #0: 1147
Received full command #1: 1148
Received full command #2: 1149
... and it runs for another hour or two, before hanging again. I'm not physically moving either sender or receiver - they're within a foot of each other - so it's not range. Though I have tried disconnecting the Arduino, and repowering it, and they do reconnect without a problem within the still-running Python process.
The Arduino code, though I don't think its as relevant, is here:
long n = 1;
void setup()
{
Serial.begin(9600);
// HC-05 default serial speed for communcation mode is 9600
Serial1.begin(9600);
}
void loop()
{
Serial1.print("<");
Serial1.print(n);
Serial1.print(">");
if(Serial1.available() > 0){ // Checks whether data is comming from the serial port
Serial.println(Serial1.readString());} // Reads the data from the serial port
delay(1000);
n++;
}
Thanks for any help or suggestions!
