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CAN is not working without Ticker

Topic last updated 05 May 2017, by Ludger Frings. 2 replies
Ludger Frings
04 May 2017

Hello there,

I'm currently working on a STM32F469I-Disco Board. I'm successfully using CAN and TouchScreen for my application. At the moment I'm using the CAN example program sending a value each second on the bus.

But once I try to call the send funtion with e.g. a touch press, my compiler gives me the following error:

"No instance of constructor "mbed::CANMessage::CANMessage" matches the argument list in "main.cpp" - pointing towards "CANMessage"

In short, this is working:

Works

Ticker ticker; // Define ticker

void send() {
    if(can2.write(CANMessage(1337, &npressed, 1))) {
        sprintf((char*)text, "Message sent: %d", counter);
        lcd.DisplayStringAt(100, 100, (uint8_t *)&text, LEFT_MODE);
        counter++;
    }
    led1 = !led1;
}
...
void main(){
ticker.attach(&send, 1); // Call function every second
}

This not:

Not working

...
x = TS_State.touchX[idx];
y = TS_State.touchY[idx];
        if (y > 100 && y < 150)
        {
            if(x > 100 && x < 330) // "Press me" Button
            {
                can2.frequency(500000);
                can2.write(CANMessage(1337, &npressed, 1));
            }  
...

Any idea how to fix it?

Best, ludgerf321

Zoltan Hudak
04 May 2017

Hello Ludger,
You don't show how npressed is declared but it seems that in the second case it isn't a char variable. Because the CANMessage constructor requires a const char* as second argument

CANMessage(int _id, const char *_data, char _len = 8, CANType _type = CANData, CANFormat _format = CANStandard);

casting &npresseed to char* as follows 

can2.write(CANMessage(1337, (const char*)&npressed, sizeof(npressed)));

or 

can2.write(CANMessage(1337, (char*)&npressed, sizeof(npressed)));

should fix the issue.

NOTE: As an alternative to the built in CANMessage class, to simplify adding/getting data to/from a CAN message, I have published a library. If you are interested you can have look at this demo how it works.

Ludger Frings
05 May 2017

Hello Zoltan,

sure that was the point! Thanks a lot, also for your great library!

Best, Ludger