Python-CAN 脚本接收一半的预期 CAN 消息

Question

I have written a Python script utilizing the Python-CAN library which records received CAN messages at a 1 second rate for 5 minutes, before logging all the messages into a file and exiting. The computer has a CAN module which is connecting to the CAN bus. (The other device on the bus is an engine) I communicate with it using the SocketCAN interface.

The test engine system that this computer is connected to is sending around 114 messages at what I believe is a 250kb baud rate. I am expecting to see 114 messages recorded in the file for each 1 second period, but instead I'm seeing about half that count. (~65 messages)

Could it be possible that the engine's ECU is set to a 500kb baud rate, and that's why I'm not getting the count I am expecting? I would think there would be no communication if the baud rates do not match, but I do not have physical access to the system because I'm sending the script remotely through an OTA update and not running it myself. (The device is headless, but is setup to run the script on startup) I just see the log files that are generated.

Here is the python code:

(A note, I have code parsing the received messages into the contained signals, but I did not include this code here because it happens at the end, and it is not relevant)

class logging:

    def __init__(self):
        #Dictionary to hold received CAN messages
        self.message_Dict = {}

        #List to hold queued dictionaries
        self.message_Queue = []

        #A "filters" object is also created here, but I did not include it
        #I have verified the filters are correct on my test system

    def main(self):

        #Record the current time
        currentTime = datetime.datetime.now()

        #Record the overall start time
        startTime = datetime.datetime.now()

        #Record the iteration start time
        lastIterationStartTime = currentTime

        #Create the CanBus that will be used to send and receive CAN msgs from the MCU
        canbus = can.interfaces.socketcan.SocketcanBus(channel='can0', bitrate=250000)
        #These filters are setup correctly, because all the messages come through
        #on my test system, but I did not include them here
        canbus.set_filters(self.Filters)

        # Creating Listener filters and notifier
        listener = can.Listener()

        #Main loop
        while 1:        

            #create a variable to hold received data
            msg2 = canbus.recv()

            #Record the current time
            currentTime = datetime.datetime.now()

            #If a valid message is detected
            if(msg2 != None):
               if(len(msg2.data) > 0):
                   try:                                
                       #Save the message data into a queue (will be processed later)
                       self.message_Dict[msg2.arbitration_id] = msg2.data

                   except:
                       print("Error in storing CAN message")

            #If 1 second has passed since the last iteration, 
            #add the dictionary to a new spot in the queue
            if((currentTime - lastIterationStartTime) >= datetime.timedelta(seconds=1)):

                #Add the dictionary with messages into the queue for later processing
                messageDict_Copy = self.message_Dict.copy()
                self.message_Queue.append(messageDict_Copy)

                print("Number of messages in dictionary: " + str(len(self.message_Dict)) + " 
                   Number of reports in queue: " + str(len(self.message_Queue)))

                #Clear the dictionary for new messages for every iteration
                self.message_Dict.clear()

                #Record the reset time
                lastIterationStartTime = datetime.datetime.now()
            
            #Once 5 minutes of data has been recorded, write to the file
            if((currentTime - startTime) > datetime.timedelta(minutes=5)):
                
                #Here is where I write the data to a file. This is too long to include

                #Clear the queue
                self.message_Queue = []

                #Clear the dictionary for new messages for every iteration
                self.message_Dict.clear()

#When the script is run, execute the Main method
if __name__ == '__main__':  
    mainClass = logging()
    mainClass.main()

I appreciate any ideas or input you have. Thank you

Answer 1

In my experience, most of the engine's ECU usually uses 250kb, but the newest ones are using 500kb. I would suggest you too also try the both.

Also, the messages will only come to the bus if they have been sent, it seems silly but for example a truck, if you don't step on the accelerator the messages referring to the accelerator will not appear. So, maybe you need to check if all components are being using as you expect. The lib of can-utils has a 'Can sniffer' that can also help you.

I suggest you to use 'can-utils' to help you in that. It is a powerful tool to can analyses.

Did you try to loop the baudrate? Maybe can also help to find another.