CAN通信的由来

为适应“减少线束的数量”、“通过多个LAN，进行大量数据的高速通信”的需要，1986 年德国电气商博世公司开发出面向汽车的CAN 通信协议。CAN属于现场总线的范畴，它是一种有效支持分布式控制或实时控制的串行通信网络。

CAN通信格式

CAN通信共有5种，分别为数据帧、遥控帧、错误帧、过载帧、帧间隔。数据帧格式由下图所示，分为标准格式和拓展格式，笔者目前仅使用到标准数据帧，使用其中的64bits数据段进行CAN节点间的数据交互，以ID号区分数据类型。注意ACK！实际波形中彼己电平高度不一

CAN通信配置

①初始化CAN的映射GPIO，使用TI封装好的函数初始化CAN，选择CAN时钟源，设置波特率，使能CAN中断触发源，开启CAN；

void InitCana(void)
{InitCanaGpio();//// Initialize the CAN controller//CANInit(CANA_BASE);//// Setup CAN to be clocked off the M3/Master subsystem clock//CANClkSourceSelect(CANA_BASE, 0);//// Set up the bit rate for the CAN bus.  This function sets up the CAN// bus timing for a nominal configuration.  You can achieve more control// over the CAN bus timing by using the function CANBitTimingSet() instead// of this one, if needed.// In this example, the CAN bus is set to 500 kHz.  In the function below,// the call to SysCtlClockGet() is used to determine the clock rate that// is used for clocking the CAN peripheral.  This can be replaced with a// fixed value if you know the value of the system clock, saving the extra// function call.  For some parts, the CAN peripheral is clocked by a fixed// 8 MHz regardless of the system clock in which case the call to// SysCtlClockGet() should be replaced with 8000000.  Consult the data// sheet for more information about CAN peripheral clocking.//CANBitRateSet(CANA_BASE, 200000000, 200000);    // 波特率200kbps//// Enable interrupts on the CAN peripheral.  This example uses static// allocation of interrupt handlers which means the name of the handler// is in the vector table of startup code.  If you want to use dynamic// allocation of the vector table, then you must also call CANIntRegister()// here.//CANIntEnable(CANA_BASE, CAN_INT_MASTER | CAN_INT_ERROR | CAN_INT_STATUS);//// Enable the CAN for operation.//CANEnable(CANA_BASE);//// Enable CAN Global Interrupt line0//CANGlobalIntEnable(CANA_BASE, CAN_GLB_INT_CANINT0);
}

②确定收发缓存数组、ID号；

//  CAN通信
unsigned char ucRXMsgData1[8];   // CAN接受数据
unsigned char ucTXMsgData2[8];   // CAN发送数据
unsigned char ucTXMsgData3[8];   // CAN发送数据
unsigned char ucTXMsgData4[8];   // CAN发送数据
unsigned char ucTXMsgData5[8];   // CAN发送数据
unsigned char ucTXMsgData6[8];   // CAN发送数据tCANMsgObject sRXCANMessage1 = {RX_MSG_OBJ_ID1, 0, 2, 8, ucRXMsgData1};    // CAN接收结构体  MSG_OBJ_RX_INT_ENABLE = 2
tCANMsgObject sTXCANMessage2 = {TX_MSG_OBJ_ID2, 0, 1, 8, ucTXMsgData2};    // CAN发送结构体  MSG_OBJ_TX_INT_ENABLE = 1
tCANMsgObject sTXCANMessage3 = {TX_MSG_OBJ_ID3, 0, 1, 8, ucTXMsgData3};    // CAN发送结构体  MSG_OBJ_TX_INT_ENABLE = 1
tCANMsgObject sTXCANMessage4 = {TX_MSG_OBJ_ID4, 0, 1, 8, ucTXMsgData4};    // CAN发送结构体  MSG_OBJ_TX_INT_ENABLE = 1
tCANMsgObject sTXCANMessage5 = {TX_MSG_OBJ_ID5, 0, 1, 8, ucTXMsgData5};    // CAN发送结构体  MSG_OBJ_TX_INT_ENABLE = 1
tCANMsgObject sTXCANMessage6 = {TX_MSG_OBJ_ID6, 0, 1, 8, ucTXMsgData6};    // CAN发送结构体  MSG_OBJ_TX_INT_ENABLE = 1

③根据自己的通信机制，封装好CAN通信收发函数；

void CANA_TX(void)
{unsigned int T_switch = 0;  // 选择数据发送CANA_TX_FRAME_CNT = CANA_TX_FRAME_CNT + 1;      // 帧计数自增
//    CANA_TX_FRAME_CNT = CANA_TX_FRAME_CNT & 0xFF;   // 帧计数达到255后清零，循环计数T_switch = CANA_TX_FRAME_CNT % 5;switch(T_switch){case 0:ucTXMsgData2[0] = CAN_CNT_delta & 0xFF;    // 帧计数ucTXMsgData2[1] = 0; // ...此处略去ucTXMsgData2[2] = 0; // ...此处略去ucTXMsgData2[3] = 0; // ...此处略去ucTXMsgData2[4] = 0; // ...此处略去ucTXMsgData2[5] = 0; // ...此处略去ucTXMsgData2[6] = 0; // ...此处略去ucTXMsgData2[7] = 0; // ...此处略去CanaMessageSet(TX_MSG_OBJ_ID2, &sTXCANMessage2, MSG_OBJ_TYPE_TX);break;case 1:ucTXMsgData3[0] = CAN_CNT_delta & 0xFF;    // 帧计数ucTXMsgData3[1] = 0; // ...此处略去ucTXMsgData3[2] = 0; // ...此处略去ucTXMsgData3[3] = 0; // ...此处略去ucTXMsgData3[4] = 0; // ...此处略去ucTXMsgData3[5] = 0; // ...此处略去ucTXMsgData3[6] = // ...此处略去ucTXMsgData3[7] = // ...此处略去CanaMessageSet(TX_MSG_OBJ_ID3, &sTXCANMessage3, MSG_OBJ_TYPE_TX);break;case 2:ucTXMsgData4[0] = CAN_CNT_delta & 0xFF;    // 帧计数ucTXMsgData4[1] = // ...此处略去ucTXMsgData4[2] = // ...此处略去ucTXMsgData4[3] = // ...此处略去ucTXMsgData4[4] = // ...此处略去ucTXMsgData4[5] = // ...此处略去ucTXMsgData4[6] = // ...此处略去ucTXMsgData4[7] = // ...此处略去CanaMessageSet(TX_MSG_OBJ_ID4, &sTXCANMessage4, MSG_OBJ_TYPE_TX);break;case 3:ucTXMsgData5[0] = CAN_CNT_delta & 0xFF;    // 帧计数ucTXMsgData5[1] = // ...此处略去ucTXMsgData5[2] = // ...此处略去ucTXMsgData5[3] = // ...此处略去ucTXMsgData5[4] = // ...此处略去ucTXMsgData5[5] = // ...此处略去ucTXMsgData5[6] = // ...此处略去ucTXMsgData5[7] = // ...此处略去CanaMessageSet(TX_MSG_OBJ_ID5, &sTXCANMessage5, MSG_OBJ_TYPE_TX);break;case 4:ucTXMsgData6[0] = CAN_CNT_delta & 0xFF;    // 帧计数ucTXMsgData6[1] = // ...此处略去ucTXMsgData6[2] = // ...此处略去ucTXMsgData6[3] = // ...此处略去ucTXMsgData6[4] = // ...此处略去ucTXMsgData6[5] = // ...此处略去ucTXMsgData6[6] = // ...此处略去ucTXMsgData6[7] = // ...此处略去CanaMessageSet(TX_MSG_OBJ_ID6, &sTXCANMessage6, MSG_OBJ_TYPE_TX);CANA_TX_Active_Flag = 0;break;default:break;}if(CANA_TX_FRAME_CNT >= 254){CANA_TX_FRAME_CNT = 0;}
}
void CANA_RX(void)
{if((CANA_errorFlag == 0) && (CANA_RX_Flag == 1)){RX_FRAME_CANA.CNT = (Uint16)ucRXMsgData1[0]; // 字节1RX_FRAME_CANA.x= (Uint16)(((ucRXMsgData1[1] & 0xF0) >> 4) & 0x0F);   // 字节2HRX_FRAME_CANA.xx = (Uint16)ucRXMsgData1[1] & 0x0F;          // 字节2LRX_FRAME_CANA.xxx= (Uint16)(((ucRXMsgData1[2] & 0xF0) >> 4) & 0x0F);    // 字节3HRX_FRAME_CANA.xxxx= (Uint16)ucRXMsgData1[2] & 0x0F;               // 字节3LRX_FRAME_CANA.xxxxx= ((Uint16)(ucRXMsgData1[3] & 0xFF)) * 0.2;      // 字节4RX_FRAME_CANA.xxxxxx= ((Uint16)(ucRXMsgData1[4] & 0xFF)) * 196.08;  // 字节5RX_FRAME_CANA.xxxxxxx= ((int)(((ucRXMsgData1[5] & 0xFF) << 8 ) | (ucRXMsgData1[6] & 0xFF))) * 0.02;    // 字节6 字节7}
}

④使用中断服务函数，传输接收发送结构体；

interrupt void CANA0_ISR(void)
{/************************************************************Description:CANA0中断服务程序用于检测中断产生原因，发送接收上位机数据************************************************************/uint32_t status;//// Read the CAN-A interrupt status to find the cause of the interrupt//status = CANIntStatus(CANA_BASE, CAN_INT_STS_CAUSE);//// If the cause is a controller status interrupt, then get the status//if(status == CAN_INT_INT0ID_STATUS){//// Read the controller status.  This will return a field of status// error bits that can indicate various errors.  Error processing// is not done in this example for simplicity.  Refer to the// API documentation for details about the error status bits.// The act of reading this status will clear the interrupt.//status = CANStatusGet(CANA_BASE, CAN_STS_CONTROL);//// Check to see if an error occurred.//if(((status  & ~(CAN_ES_TXOK | CAN_ES_RXOK)) != 7) &&((status  & ~(CAN_ES_TXOK | CAN_ES_RXOK)) != 0)){//// Set a flag to indicate some errors may have occurred.//CANA_errorFlag = 1;}}//// Check if the cause is the CAN-A receive message object 1//else if(status == RX_MSG_OBJ_ID1){//// Get the received message//CANMessageGet(CANA_BASE, RX_MSG_OBJ_ID1, &sRXCANMessage1, true);//// Getting to this point means that the RX interrupt occurred on// message object 1, and the message RX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, RX_MSG_OBJ_ID1);//// Since the message was received, clear any error flags.//CANA_errorFlag = 0;CANA_RX_Flag = 1;CANA_TX_Active_Flag = 1;Timer_CANA_TX_1ms = 0;}//// Check if the cause is the CAN-A send message object 1//else if(status == TX_MSG_OBJ_ID2){//// Getting to this point means that the TX interrupt occurred on// message object 1, and the message TX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, TX_MSG_OBJ_ID2);//// Since the message was sent, clear any error flags.//CANA_errorFlag = 0;}//// Check if the cause is the CAN-A send message object 1//else if(status == TX_MSG_OBJ_ID3){//// Getting to this point means that the TX interrupt occurred on// message object 1, and the message TX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, TX_MSG_OBJ_ID3);//// Since the message was sent, clear any error flags.//CANA_errorFlag = 0;}//// Check if the cause is the CAN-A send message object 1//else if(status == TX_MSG_OBJ_ID4){//// Getting to this point means that the TX interrupt occurred on// message object 1, and the message TX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, TX_MSG_OBJ_ID4);//// Since the message was sent, clear any error flags.//CANA_errorFlag = 0;}//// Check if the cause is the CAN-A send message object 1//else if(status == TX_MSG_OBJ_ID5){//// Getting to this point means that the TX interrupt occurred on// message object 1, and the message TX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, TX_MSG_OBJ_ID5);//// Since the message was sent, clear any error flags.//CANA_errorFlag = 0;}//// Check if the cause is the CAN-A send message object 1//else if(status == TX_MSG_OBJ_ID6){//// Getting to this point means that the TX interrupt occurred on// message object 1, and the message TX is complete.  Clear the// message object interrupt.//CANIntClear(CANA_BASE, TX_MSG_OBJ_ID6);//// Since the message was sent, clear any error flags.//CANA_errorFlag = 0;}//// If something unexpected caused the interrupt, this would handle it.//else{//// Spurious interrupt handling can go here.//}//// Clear the global interrupt flag for the CAN interrupt line//CANGlobalIntClear(CANA_BASE, CAN_GLB_INT_CANINT0);//// Acknowledge this interrupt located in group 9//PieCtrlRegs.PIEACK.all = PIEACK_GROUP9;}

实验验证

采用上位机（PC）发1帧，下位机（DSP）应答5帧的方式，实现遥控与遥测，要想实现更为精准的定时，则可以采取其他的方式，比如TT-CAN等。上位机发送间隔6ms，下位机应答间隔1ms。上位机数据帧ID（00000000001），下位机数据帧ID（00000000010、00000000011、00000000100、00000000101、00000000110）。使用ZLG的示波器，因为他自带CAN通信解码功能，使用起来非常方便。
上位机遥控帧：

下位机遥测帧①

下位机遥测帧⑤

结束语

笔者对于CAN的使用，仅停留在数据帧这一简单的帧种类上，以后若是有项目需要，则再补充学习其他的帧种类。TI对于CAN的支持比较到位，我们可以直接调用相应的函数，即可实现功能。当然规则越明细，开发人员对其标准化程度会越高，但使用灵活度、自由度变差。

参考资料目录

《TMS320F2837xS Delfino Microcontrollers Datasheet》Memory章节
《TMS320F2837xS Delfino Microcontrollers Technical Reference Manual》CAN章节
RENESAS应用手册《CAN入门书》
C2000Ware有关CAN的所有例程