CAN messaging

Requirements: [HW] Controller

ARM-CAN controller board LM3S5632 MCU is programmed with the help of Texas Instruments (former Luminary Micro) StellarisWare software library. The library includes all the functions to alter microcontroller's registers. LM3S5632 incorporates CAN 2.0 controller with 32 message objects which can be used to automatically transmit and receive messages.

Most common functions to deal with CAN controller are CANMessageSet and CANMessageGet. The first one is used to configure one of the 32 message objects to send or receive a message, another one is used to read the message which was sent or received. They both use tCANMsgObject structure to specify message ID, mask, flags and payload.

The following program demonstrates how to set up CAN controller and wait for a message:

//*****************************************************************************
//
// CAN message receiving.
//
//*****************************************************************************
 
#include <inc/hw_ints.h>
#include <inc/hw_memmap.h>
#include <inc/hw_types.h>
#include <driverlib/sysctl.h>
#include <driverlib/can.h>
 
//*****************************************************************************
//
// Main function.
//
//*****************************************************************************
int main(void)
{	
	tCANMsgObject psMsg;
	unsigned char pucData[8];
 
	//
	// Set the clocking to run from the PLL at 50MHz
	//
	SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
	   SYSCTL_XTAL_8MHZ);
 
	//
	// Enable peripherals.
	//	
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_CAN0);		
 
	//
	// Configure CAN pins.
	//
	GPIOPinTypeCAN(GPIO_PORTD_BASE, GPIO_PIN_0 | GPIO_PIN_1);	
 
	//
	// Enable the CAN controller.
	//    
	CANInit(CAN0_BASE);
	CANBitRateSet(CAN0_BASE, SysCtlClockGet(), CAN_BITRATE);
	CANEnable(CAN0_BASE);	
 
	//
	// Create receive message object.
	//	
	psMsg.ulMsgID     = 0x01;
	psMsg.ulMsgIDMask = 0xFF;
	psMsg.ulFlags     = MSG_OBJ_NO_FLAGS;	
	psMsg.pucMsgData  = pucData;
 
	//
	// Set message object on box 1.
	//
	CANMessageSet(CAN0_BASE, 1, &psEchoMsg, MSG_OBJ_TYPE_RX);
 
	//
	// Loop forever.
	//
	while (1)
	{	
		//
		// CAN message received ?
		//
		if (CANStatusGet(CAN0_BASE, CAN_STS_NEWDAT) & 1)
		{
			//
			// Get the message.
			//
			CANMessageGet(CAN0_BASE, CAN_MSG_OBJ_RX, &psMsg, true);
 
			//
			// Access pucData here.
			// To get the length of the data read psMsg.ulMsgLen
			//
		}
	}
}