Program running on RPi 3b+ Very Strange Behavior - Out of Bound Index

[MadMacks]

Another quick question...

In the code block...

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while True:     if p.waitForNotifications(1.0):         # handleNotification() was called         continue       print "Waiting..."     # Perhaps do something else here

What is the "(1.0)" value do? I understand that a logical test getting a "1" resolves to True, but what does a "1.0" do? Is that some special Python boolean thing?

[MadMacks]

OK... It's been an interesting journey but I think I have a better understanding now.

In the original code tgalarneau had the "write MQTT" statements are inside the Delegate code block, so when the device responds and triggers the delegate it figures out which response it is getting and then parses it and writes the MQTT message.

When I refactored his code I did not take that into account, and was doing my MQTT message writing as if it was procedural code. Sometimes it worked, sometimes not, based on whether or not the delegate had received both of the result messages. I think that explains the randomness issue. I'll do some rework and see if I can take that delegate processing into account...

[MadMacks]

Another quick question...

In the code block...

1 2 3 4 5 6 7

while True:     if p.waitForNotifications(1.0):         # handleNotification() was called         continue       print "Waiting..."     # Perhaps do something else here

What is the "(1.0)" value do? I understand that a logical test getting a "1" resolves to True, but what does a "1.0" do? Is that some special Python boolean thing?

Guess I just answered the question...

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>>> if(1): ...     print("true") ... else: ...     print("false") ... true >>> if(1.0): ...     print("true") ... else: ...     print("false") ... true

[deanhystad]

1.0 is the timeout for Peripheral.waitForNotifications(timeout_in_seconds). That actually does appear in the documentation.

http://ianharvey.github.io/bluepy-doc/

In particular here:

http://ianharvey.github.io/bluepy-doc/peripheral.html

[MadMacks]

Odd that they used something other than an integer value, what's the point of the 1.0 precision.
Guess I'm to easily confused by some examples...

So all the code is doing is looping while waiting for a response, and if it gets one it gets out of the code block and moves on...right?

[deanhystad]

It takes a number. The number can be an int or a float. You could wait for 1.5 seconds or 2 seconds. I can easily imagine having many peripherals and using a loop to monitor their progress.

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for peripheral in peripherals:     if peripheral.waitForNotification(0.1):         # Notification received.  Process and remove peripheral from the monitor queue.         peripheral.do_something()         peripherals.remove(peripheral)

[MadMacks]

So, just to close out this thread I thought I'd post a now working version of the python code. It doesn't (yet) use the nicer code unpacking that deanhystad suggested but it works...

Thank you for the feedback as it was invaluable in helping me figure this stuff out...

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#!/usr/bin/env python3 # This code should be run as SUDO as it does low level BLE scanning. # # Run it as follows: # #   sudo python jbd-bms-mqtt.py -n "Cabin 580ah" -i 0 -t solar #   or #   sudo python jbd-bms-mqtt.py -a "a4:c1:38:30:c2:8e" -i 0 -t solar # # This will scan for a bluetooth device called "Cabin 580ah" and extract its # bluetooth address, or, use the passed address if provided, then try and attach # to the BMS and read a set if variables, one time, and then publish a MQTT # message with those variables to the Topic "solar". # # USAGE NOTE # If you use a value other than 0 for the -i parm the program will loop forever # and read the BMS values every X minutes based on the value you passed. This is # not recommended as a long term method to run the script, as it could cause # resource issues in the python environment. For an ongoing run please use a # cron job to control run times and pass a 0 for the -i argument... # # In addition, if you run this program via a manual shell loop instead of using # cron, and someone attached to the BMS using a bluetooth app (like XiaoxiangBMS # or SmartBMSUtility) the code will fail when it attempts to connect (as the other # app has the connection) and will throw an exception. If you started it intending # it to run "forever" in a terminal window you will not realize it's failed. # # If cron is used, at least the process will be kicked off again based on the cron # process and try to reconnect again, automatically... # # You've been warned!   from bluepy.btle import Peripheral, DefaultDelegate, BTLEException from bluepy.btle import Scanner, DefaultDelegate import sys import struct import argparse import json import time import binascii import atexit import paho.mqtt.client as paho     def disconnect():     mqtt.disconnect()     print("broker disconnected")     def cellinfo1(data):  # process battery info     print("Processing (dd03) battery info...")     infodata = data     # Unpack into variables, skipping header bytes 0-3     volts, amps, remain, capacity, cycles, mdate, balance1, balance2 = struct.unpack_from('>HhHHHHHH', infodata, 4)     volts = volts / 100     amps = amps / 100     capacity = capacity / 100     remain = remain / 100     global ginfo     ginfo.append(volts)     ginfo.append(amps)     ginfo.append(capacity)     ginfo.append(remain)     print(ginfo)     time.sleep(timeSleep)         def cellvolts1(data):  # process cell voltages     print("Processing (dd04) cell volts message...")     celldata = data     # Unpack into variables, skipping header bytes 0-3     cell1, cell2, cell3, cell4 = struct.unpack_from('>HHHH', celldata, 4)     global ginfo     ginfo.append(cell1)     ginfo.append(cell2)     ginfo.append(cell3)     ginfo.append(cell4)     print(ginfo)     time.sleep(timeSleep)     class MyDelegate(DefaultDelegate):  # When the device replies this code is invoked to deal with it     def __init__(self):         DefaultDelegate.__init__(self)       def handleNotification(self, cHandle, data):         hex_data = binascii.hexlify(data)       # Given raw bytes, get an ASCII string representing the hex values         text_string = hex_data.decode('utf-8')  # Check incoming data for routing to decoding routines         if text_string.find('dd03') != -1:      # x03             cellinfo1(data)                     # Decode and process BMS info         elif text_string.find('dd04') != -1:    # x04             cellvolts1(data)                    # Decode and process cell info         else:             print("Why Am I Here? What is this data", text_string)     # Mainline Code   # Process command line arguments and set up variables parser = argparse.ArgumentParser(description='Fetches and outputs JBD bms data') parser.add_argument("-n", "--name", help="BLE Device Name", required=False) parser.add_argument("-a", "--address", help="BLE Device Address", required=False) parser.add_argument("-i", "--interval", type=int, help="Read interval in minutes, 0=One & Done", required=True) parser.add_argument("-t", "--topic", help="MQTT Topic name", required=True) args = parser.parse_args() loopMinutes = args.interval * 60         # Takes the input value and turns it into minutes topic = args.topic                       # Topic to use when posting to MQTT bleName = args.name                      # BLE device Name that will be scanned for to get address bleAddrP = args.address                  # BLE address that will be used rather than a BLE name timeSleep = 1                            # Used to slow things down a bit in case of timing issues ginfo = list()                           # Global list to hold elements from the various requests broker = "192.168.1.98"                  # Change this to your MQTT broker address port = 1883                              # Default port that MQTT is listening on   # Resolve the BLE device address using a name or a provided address if not bleAddrP and not bleName:     sys.exit("Process needs either a ble Name or ble Address...Halting!") elif bleName:     print("Searching for ble Name = '%s'" % bleName)     scanner = Scanner()     devices = scanner.scan(5)             # Scan for 5 seconds     print("============ Scanning Results  ==============")     for dev in devices:         for (adtype, desc, value) in dev.getScanData():             print("Device = '%s'   Name = '%s'" % (dev.addr, value))             if value == bleName:                 print("=========== Found It ==============")                 print("Name = %s" % value)                 print("Device = %s" % dev.addr)                 print("RSSI = %d dB" % dev.rssi)                 print("===================================")                 bleAddr = dev.addr else:     bleAddr = bleAddrP    # Use the command line parm address     try:                      # If the variable was created above the BLE device was found     bleAddr except NameError:     sys.exit("Do not have a usable BLE device address...Halting!")   # Main Loop Logic Begins Here while True:       try:                  # Attempt a connection with the BMS via BLE         print('Attempting to connect...')         bms = Peripheral(bleAddr, addrType="public")     except BTLEException as ex:         time.sleep(30)    # timeSleep not used here, this waits 30 seconds between attempts         print('1st attempt failed, trying 2nd time to connect...')         bms = Peripheral(bleAddr, addrType="public")     except NameError:         sys.exit("Can not connect to the BLE device...Halting!")         # This means something went wrong as there is a ble address to use but it could not         # be connected. Maybe some other application has the connection already and someone         # forgot to disconnect when they were done configuring the BMS.     else:         print('Connected...', bleAddr)       atexit.register(disconnect)     # run the disconnect function when with the loop     mqtt = paho.Client("control3")  # create and connect mqtt client     mqtt.connect(broker, port)     bms.setDelegate(MyDelegate())   # setup BlueTooth process delegate to get returned notifications       # write x03 record to request battery info     resultx03 = bms.writeCharacteristic(0x15, b'\xdd\xa5\x03\x00\xff\xfd\x77', False)     bms.waitForNotifications(5)     # waiting 5 seconds as less seems to cause missed notifications       # write x04 record to request cell volts info     resultx04 = bms.writeCharacteristic(0x15, b'\xdd\xa5\x04\x00\xff\xfc\x77', False)     bms.waitForNotifications(5)     # waiting 5 seconds as less seems to cause missed notifications     time.sleep(timeSleep)       # Disconnect from BMS BLE connection. This allows other applications and tools the chance     # to connect to the BMS via Bluetooth.     bms.disconnect()           # Load the JSON message with the merged BMS data and send it via MQTT     time.sleep(timeSleep)     gvolts = ginfo[0]     gamps = ginfo[1]     gcapacity = ginfo[2]     gremain = ginfo[3]     gcellvolt1 = ginfo[4]     gcellvolt2 = ginfo[5]     gcellvolt3 = ginfo[6]     gcellvolt4 = ginfo[7]     message0 = {         "topic": topic,         "volts": gvolts,         "amps": gamps,         "capacity": gcapacity,         "remain": gremain,         "cell1": gcellvolt1,         "cell2": gcellvolt2,         "cell3": gcellvolt3,         "cell4": gcellvolt4     }     ret = mqtt.publish(topic, payload=json.dumps(message0), qos=0, retain=False)       if loopMinutes != 0:        # Loop unless interval is 0, otherwise one & done         while len(ginfo) > 0:   # If looping the ginfo list needs to be cleaned or it just grows and grows             del ginfo[0]         time.sleep(loopMinutes)     else:         break