CLR_E_NULL_REFERENCE - Can Bus during receive event

NETMF & Gadgeteer
1

Hi,

I finally got my CAN setup to start sending messages. (Ended up being the MCP2551 transceivers not playing nice).

I have two transceivers setup on the board. I can send messages no problem. This occurs no matter what speed I set in bitrate.

But when the DataReceivedEvent fires its throwing the following exception.

(Let me know if I need to throw up a schematic. But its very basic, two transceivers on the board, termination. Typical 2 node CAN set up. I have verified the data on the bus with a logic analyzer. )

Here is the exception:

>>> can_DataReceivedEvent <<< Chl 2
    #### Exception System.NullReferenceException - CLR_E_NULL_REFERENCE (3) ####
    #### Message: 
    #### MFConsoleApplication1.Program::canTwo_DataReceivedEvent [IP: 0011] ####
    #### GHI.Premium.Hardware.CANDataReceivedEventHandler::Invoke [IP: 0000] ####
    #### GHI.Premium.Hardware.CAN::nativeEventDispatcher_OnInterrupt [IP: 003f] ####
    #### GHI.Premium.System.InternalEvent::nativeEventDispatcher_OnInterrupt [IP: 0025] ####
A first chance exception of type 'System.NullReferenceException' occurred in MFConsoleApplication1.exe
An unhandled exception of type 'System.NullReferenceException' occurred in MFConsoleApplication1.exe

And my current code.

using System;
using System.Threading;
using GHI.Premium.Hardware;
using Microsoft.SPOT;
using Microsoft.SPOT.Hardware;

namespace MFConsoleApplication1
{
    public class Program
    {
        private static CAN.Message[] msgList;

        public static void Main()
        {
            //First lets set date/time
            Utility.SetLocalTime(new DateTime(2013, 09, 15, 08, 55, 00));

            uint bitRate = GetBitRateConfig_120MHZ(Bitrate.BITRATE_500k);

            CAN can = new CAN(CAN.Channel.Channel_1, bitRate);

            CAN canTwo = new CAN(CAN.Channel.Channel_2, bitRate);

            //canTwo.Reset();

            can.DataReceivedEvent += can_DataReceivedEvent;
            can.ErrorReceivedEvent += can_ErrorReceivedEvent;

            canTwo.DataReceivedEvent += canTwo_DataReceivedEvent;
            canTwo.ErrorReceivedEvent += canTwo_ErrorReceivedEvent;

            int clock = 1;

            CAN.Message sendMessage = new CAN.Message();

            
            sendMessage.ArbID = 0x7E5;

            sendMessage.Data[0] = (byte)clock;
            sendMessage.Data[1] = 0x78;
            sendMessage.Data[2] = 0x5F;
            sendMessage.Data[3] = 0xFF;
            sendMessage.Data[4] = 0x3B;
            sendMessage.Data[5] = 0x00;
            sendMessage.Data[6] = 0x00;
            sendMessage.Data[7] = 0x4C;

            if (clock == int.MaxValue - 1)
                clock = 0;

            clock ++;

            CAN.Message[] messages = new[] {sendMessage};

            while (true)
            {

                int numberMessagesPosted = can.PostMessages(messages, 0, messages.Length);
                Debug.Print("Number of messages posted: "+numberMessagesPosted);
                var test = can.TransmitErrorCount;

                if (test > 1)
                    Debug.Print(test.ToString());

                Thread.Sleep(500);
            }
        }

        static void canTwo_ErrorReceivedEvent(CAN sender, CANErrorReceivedEventArgs args)
        {
            Debug.Print(">>> can_ErrorReceivedEvent <<< Chl 2");

            switch (args.Error)
            {
                case CAN.Error.Overrun:
                    Debug.Print("Overrun error. Message lost");
                    break;

                case CAN.Error.RXOver:
                    Debug.Print("RXOver error. Internal buffer is full. Message lost");
                    break;

                case CAN.Error.BusOff:
                    Debug.Print("BusOff error. Reset CAN controller.");
                    sender.Reset();
                    break;
            }
        }

        static void canTwo_DataReceivedEvent(CAN sender, CANDataReceivedEventArgs args)
        {
            Debug.Print(">>> can_DataReceivedEvent <<< Chl 2");
            msgList = new CAN.Message[500];            

            // read as many messages as possible
            int count = sender.GetMessages(msgList, 0, msgList.Length);
            for (int i = 0; i < count; i++)
            {
                string m = ("Data: " + msgList[i].Data[0].ToString("X") + " " + msgList[i].Data[1].ToString("X") + " " + msgList[i].Data[2].ToString("X") + " " + msgList[i].Data[3].ToString("X") + " "
                            + msgList[i].Data[3].ToString("X") + " " + msgList[i].Data[4].ToString("X") + " " + msgList[i].Data[5].ToString("X") + " " + msgList[i].Data[6].ToString("X") + " "
                            + msgList[i].Data[7].ToString("X"));
                Debug.Print("MSG: ID = " + msgList[i].ArbID + "DATA: " + m + "  at time = " + msgList[i].TimeStamp);
            }
        }

        private static void can_ErrorReceivedEvent(CAN sender, CANErrorReceivedEventArgs args)
        {
            Debug.Print(">>> can_ErrorReceivedEvent <<< Chl 1");

            switch (args.Error)
            {
                case CAN.Error.Overrun:
                    Debug.Print("Overrun error. Message lost");
                    break;

                case CAN.Error.RXOver:
                    Debug.Print("RXOver error. Internal buffer is full. Message lost");
                    break;

                case CAN.Error.BusOff:
                    Debug.Print("BusOff error. Reset CAN controller.");
                    sender.Reset();
                    break;
            }
        }

        private static void can_DataReceivedEvent(CAN sender, CANDataReceivedEventArgs args)
        {
            Debug.Print(">>> can_DataReceivedEvent <<< Chl 1");
            msgList = new CAN.Message[500];
            // read as many messages as possible
            int count = sender.GetMessages(msgList, 0, msgList.Length); 
            for (int i = 0; i < count; i++)
            {
                string m = ("Data: " + msgList[i].Data[0].ToString("X") + " " + msgList[i].Data[1].ToString("X") + " " + msgList[i].Data[2].ToString("X") + " " + msgList[i].Data[3].ToString("X") + " "
                            + msgList[i].Data[3].ToString("X") + " " + msgList[i].Data[4].ToString("X") + " " + msgList[i].Data[5].ToString("X") + " " + msgList[i].Data[6].ToString("X") + " "
                            + msgList[i].Data[7].ToString("X"));
                Debug.Print("MSG: ID = " + msgList[i].ArbID + "DATA: " + m + "  at time = " + msgList[i].TimeStamp);
            }
        }


        public enum Bitrate
        {
            NONE = 0,
            BITRATE_125k = 125000,
            BITRATE_250k = 250000,
            BITRATE_500k = 500000,
            BITRATE_1000k = 1000000,
        }

        /// <summary>
        /// Returns a bitrate for the internal CAN driver
        /// </summary>
        /// <param name="bitrate">Bitrate</param>
        /// <returns>CAN driver bitrate for LPC17XX</returns>
        public static uint GetBitRateConfig_120MHZ(Bitrate bitrate)
        {
            int t1 = 0;
            int t2 = 0;
            int brp = 0;

            switch (bitrate)
            {
                case Bitrate.BITRATE_125k:
                    brp = 20;
                    t1 = 16 - 1;
                    t2 = 8;
                    break;

                case Bitrate.BITRATE_250k:
                    brp = 10;
                    t1 = 16 - 1;
                    t2 = 8;
                    break;

                case Bitrate.BITRATE_500k:
                    brp = 5;
                    t1 = 16 - 1;
                    t2 = 8;
                    break;

                case Bitrate.BITRATE_1000k:
                    brp = 5;
                    t1 = 8 - 1;
                    t2 = 4;
                    break;
            }

            return (uint) (((t2 - 1) << 20) | ((t1 - 1) << 16) | ((brp - 1) << 0));
        }
    }
}
2

I don’t see where you allocate your msgList. It is null and when you try to get Length property you got the null reference exception.

3

It pasted old code. I updated it. I am instantiating a new CAN.Message list.

It appears the exception is getting thrown from unmanaged code? or CLR exception?

-Matt

4

What line throws the exception?

5 
int count = sender.GetMessages(msgList, 0, msgList.Length);

Is where the exception is thrown. (sender has a value btw)

-Matt

6

Check if sender is null.

7

It does have a value. (sender != null)

Here is the exception break in VS

An unhandled exception of type 'System.NullReferenceException' occurred in GHI.Premium.Hardware.dll

I turned off “Just My Code” and enabled all exceptions, it broke at the following line in the GHI.Premium.Hardware.CAN class

public extern int GetMessages(Message[] msg, int offset, int count);
8

And msgList is definitely not null?

9

100% sure! Here is a screen grab of all the values in scope and the exception

10

Looks like it is something for GHI to verify.

Architect is out.

11

Thanks for looking Architect!

GHI?? Help! :slight_smile:

-Matt

12

looking into it

13

Solved.

I made the assumption that the GetMessages method instantiated the individual CanMessages in the array.

Changing my code to the following fixes the issue.

int count = 0;
            // read as many messages as possible

            int recCount = sender.ReceivedMessagesCount;
            msgList = new CAN.Message[recCount];

            for(int i =0; i < msgList.Length; i++)
            {
                msgList[i] = new CAN.Message();
            }
            
            count = sender.GetMessages(msgList, 0, msgList.Length);

Thanks very much for looking into it!

-Matt

14

That makes total sense! Completely missed that :slight_smile: