DSP28035的CAN通讯程序_28035 can

CAN通讯设计

DSP/MCU的CAN接口是指芯片外设中的CAN总线控制器，其输出电平为TTL规格，如果直接将两块芯片的CANRX、CANTX引脚连接，无法实现CAN通讯。SAJ1000、TJA1050芯片是属于物理层芯片，将TTL电平信号转换为符合CAN规范的差分信号，从而实现CAN通讯。
因此，上位机与DSP进行CAN通讯时，相比于基于SCI的串口通讯，需要多加一个收发芯片模块。将DSP/MCU的CANRX引脚接入模块的RX，CANTX接入模块的TX，从而将TTL电平信号转为CAN通讯的差分信号CANH和CANL。

CAN通讯接口

一般的CAN通讯接口对外主要是CANH和CANL两个信号。

当两个具有CAN通讯接口的设备相互通讯时，两边的CANH连接，CANL也连接。高频信号传输时，信号波长相对传输线较短，信号在传输线终端会形成反射波，干扰原信号，所以需要在传输线末端加终端电阻，使信号到达传输线末端后不反射。对于低频信号则不用 CAN总线两端必须连接终端电阻才可以正常工作，终端电阻应该与通讯电缆的阻抗相同，典型值为120欧姆。其作用是匹配总线阻抗，提高数据通信的抗干扰性及可靠行。

PC调试CAN

当需要利用PC对CAN设备进行调试时，由于PC机通常没有CAN接口，也没有CAN控制器，因此需要CAN转USB模块、CAN转以太网模块等，本质上，该模块内部有一块DSP/MCU，将能够将CAN差分通讯转为PC机能够直接进行的通讯方式，如串口通讯、以太网通讯等。
由于转换模块所用的DSP/MCU中对CAN通讯的处理程序不同，因此，CAN转USB、CAN转以太网模块通常没有统一的PC上位机，针对CAN转化模块，PC上需要根据模块制造商所提供的API，设计相应合适的上位机。

目前选择的CAN转USB模块，实现了将CAN通讯转为串口通讯的功能，直接使用普通的串口调试助手即可调试CAN通讯，后期可以将原有的串口通讯、485通讯协议移植到CAN通讯上。

CAN邮箱配置

CAN通讯时，有个概念叫邮箱，一共分为了收发邮箱两类，通过配置确定邮箱为发送还是接收邮箱，每个邮箱也会有分配ID和滤波器，用于识别帧数据是否是发送给了对应的设备。当采用CAN转USB模块时，可以关闭滤波器，实现任意ID的接收。

代码配置（DSP28035为例）

main函数部分，主要是初始化程序是这样的，这些基本都是调用或者遵照TI官方示例写的

    /* Create a shadow register structure for the CAN control registers. This is
    needed, since, only 32-bit access is allowed to these registers. 16-bit access
    to these registers could potentially corrupt the register contents. This is
    especially true while writing to a bit (or group of bits) among bits 16 - 31 */

    struct ECAN_REGS ECanaShadow;
    // Step 1. Initialize System Control:
    // PLL, WatchDog, enable Peripheral Clocks
    // This example function is found in the DSP2833x_SysCtrl.c file.
    InitSysCtrl();


    // Just initalize eCAN pins for this example
    // This function is in DSP2833x_ECan.c


    // Step 3. Clear all interrupts and initialize PIE vector table:
    // Disable CPU interrupts
    DINT;

    // Initialize the PIE control registers to their default state.
    // The default state is all PIE interrupts disabled and flags
    // are cleared.
    // This function is found in the DSP2833x_PieCtrl.c file.
    InitPieCtrl();

    // Disable CPU interrupts and clear all CPU interrupt flags:
    IER = 0x0000;
    IFR = 0x0000;

    // Initialize the PIE vector table with pointers to the shell Interrupt
    // Service Routines (ISR).
    // This will populate the entire table, even if the interrupt
    // is not used in this example.  This is useful for debug purposes.
    // The shell ISR routines are found in DSP2833x_DefaultIsr.c.
    // This function is found in DSP2833x_PieVect.c.
    InitPieVectTable();

    // Interrupts that are used in this example are re-mapped to
    // ISR functions found within this file.


    InitECanGpio();

    // Step 4. Initialize all the Device Peripherals:
    // This function is found in DSP2833x_InitPeripherals.c
    // InitPeripherals(); // Not required for this example

    // In this case just initalize eCAN-A and eCAN-B
    // This function is in DSP2833x_ECan.c
    InitECan();
    ErrorCount = 0;
    PassCount = 0;

    /* Write to the MSGID field  */

    ECanaMboxes.MBOX16.MSGID.all = 0x95555554; // Extended Identifier
    ECanaMboxes.MBOX25.MSGID.all = 0x95555555; // Extended Identifier

    /* Configure Mailbox under test as a Re/Transmit mailbox */
    EALLOW;
    ECanaShadow.CANMD.all = ECanaRegs.CANMD.all;
    ECanaShadow.CANMD.bit.MD16 = 1; //rx
    ECanaShadow.CANMD.bit.MD25 = 0;//tx
    ECanaRegs.CANMD.all = ECanaShadow.CANMD.all;


    //without considering id and the data can be received
    ECanaMboxes.MBOX16.MSGID.bit.AME = 1;
    ECanaLAMRegs.LAM16.all = 0xFFFFFFFF;

    /* Enable Mailbox under test */

    ECanaShadow.CANME.all = ECanaRegs.CANME.all;
    ECanaShadow.CANME.bit.ME16 = 1;
    ECanaShadow.CANME.bit.ME25 = 1;
    ECanaRegs.CANME.all = ECanaShadow.CANME.all;


    /* Write to DLC field in Master Control reg */
    //ECanaMboxes.MBOX16.MSGCTRL.bit.DLC = 8;
    ECanaMboxes.MBOX25.MSGCTRL.bit.DLC = 8;



    ECanaRegs.CANRMP.all = 0xFFFFFC00;

    /* Write to the mailbox RAM field */

    ECanaMboxes.MBOX25.MDL.all = 0x55555555;
    ECanaMboxes.MBOX25.MDH.all = 0xAAAAAAAA;

    EDIS;

    EALLOW;

    ECanaShadow.CANMIM.all=ECanaRegs.CANMIM.all;
    ECanaShadow.CANMIM.bit.MIM16=1;
    ECanaRegs.CANMIM.all=ECanaShadow.CANMIM.all;

    ECanaShadow.CANMIL.all = ECanaRegs.CANMIL.all;
    ECanaShadow.CANMIL.all = 0;              // 1-32号邮箱中断在中断线0上产生
    ECanaRegs.CANMIL.all = ECanaShadow.CANMIL.all;

    ECanaShadow.CANGIM.all = ECanaRegs.CANGIM.all;
    ECanaShadow.CANGIM.bit.I0EN = 1 ;              //  中断线0使能
    ECanaRegs.CANGIM.all = ECanaShadow.CANGIM.all;

    ECanaShadow.CANMC.all = ECanaRegs.CANMC.all;
    ECanaShadow.CANMC.bit.STM = 0;    // 0-Normal
    ECanaRegs.CANMC.all = ECanaShadow.CANMC.all;

    EDIS;

    EALLOW;  // This is needed to write to EALLOW protected registers
    PieVectTable.ECAN0INTA = &Ecan0ISR;//R-CAN1  接收后中断函数
    EDIS;   // This is needed to disable write to EALLOW protected registers

    IER |=M_INT9;// 开CPU中断1~9(必须开放对应的CPU级中断口)

    PieCtrlRegs.PIECTRL.bit.ENPIE = 1;   // Enable the PIE block
    PieCtrlRegs.PIEIER9.bit.INTx5=1;     //R-CAN0  接收邮箱


    EINT;//开总中断
    ERTM;//使能实时中断（CPU级的）



    /* Begin transmitting */


    for(i=0; i < TXCOUNT; i++)
    {
        ECanaShadow.CANTRS.all = 0;
        ECanaShadow.CANTRS.bit.TRS25 = 1;             // Set TRS for mailbox under test
        ECanaRegs.CANTRS.all = ECanaShadow.CANTRS.all;

        do
        {
            ECanaShadow.CANTA.all = ECanaRegs.CANTA.all;
        } while(ECanaShadow.CANTA.bit.TA25 == 0 );   // Wait for TA5 bit to be set..//如果线没有连接，如果线连接错误


        ECanaShadow.CANTA.all = 0;
        ECanaShadow.CANTA.bit.TA25 = 1;               // Clear TA5
        ECanaRegs.CANTA.all = ECanaShadow.CANTA.all;

    }

    while(1)
    {
        ECanaShadow.CANRMP.all = ECanaRegs.CANRMP.all;
    }
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这里有少数需要注意是地方就是邮箱滤波器的关闭

    //without considering id and the data can be received
    ECanaMboxes.MBOX16.MSGID.bit.AME = 1;
    ECanaLAMRegs.LAM16.all = 0xFFFFFFFF;
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这两句话加在使能邮箱前，才能生效。
最后就是CAN对应的中断了，只需要按照邮箱结构体，依次读取邮箱的低位数据、高位数据和邮箱ID即可。

//
__interrupt void Ecan0ISR(void)//R  接收后进入的中断
{
    if(ECanaRegs.CANRMP.all==0x00010000)//RX get after flag and int   BOX16
    {
        ECanaRegs.CANRMP.all = 0x00010000;//clear GMIF16
        TestMbox1 = ECanaMboxes.MBOX16.MDL.all;
        TestMbox2 = ECanaMboxes.MBOX16.MDH.all;
        TestMbox3 = ECanaMboxes.MBOX16.MSGID.all;//从外部接收邮箱16的ID，16为接收邮箱（CANMD）
    }

    PieCtrlRegs.PIEACK.all = PIEACK_GROUP9;

}
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