STM CAN filter配置纪要
案例1：某工程师使用STM32F407VG开发产品，在做CAN的调试过程中发现，CAN1接收、CAN2发送，工作正常。但反过来就有问题，即CAN2收，CAN1发就无法正常接收。
后来发现CAN 过滤器配置的地方有问题。他使用STM32Cube固件库，两句关键代码如下：
sFilterConfig.FilterNumber = m; //……【1】
sFilterConfig.BankNumber = n; //……【2】
第【1】句代码就是选择某过滤器组进行初始化并配置接收过滤器。对于双CAN产品，m的值为0到27。对于单CAN产品而言，m的值为0~13。
第【2】句代码针对双CAN的STM32产品，配置CAN2可使用的过滤器组的起始编号，n取值范围为0~28.从编号为n的过滤器组到编号为27的过滤器组分配给CAN2使用。通过配置寄存器CAN2SB[5:0]@CAN_FRM确定。如果第【2】句配置不在代码中明确写出来，默认值就是14. 即硬件默认将编号为14起往后的过滤器组分配给CAN2使用。
void CanBus_Config(void)
{
CAN_InitTypeDef CAN_InitStructure;
CAN_FilterInitTypeDef CAN_FilterInitStructure;
/* CAN register init */
// CAN_DeInit();
/* CAN1 and CAN2 register init */
CAN_DeInit(CAN1);
CAN_DeInit(CAN2);
/* Struct init*/
CAN_StructInit(&CAN_InitStructure);
/*************************************************************
主机CAN配置
*************************************************************/
/* CAN cell init */
CAN_InitStructure.CAN_TTCM = DISABLE; //禁止时间触发通信模式
CAN_InitStructure.CAN_ABOM = DISABLE;
CAN_InitStructure.CAN_AWUM = DISABLE;
CAN_InitStructure.CAN_NART = DISABLE;
//CAN报文只被发送1次，不管发送的结果如何（成功、出错或仲裁丢失）
CAN_InitStructure.CAN_RFLM = DISABLE;
CAN_InitStructure.CAN_TXFP = DISABLE;
CAN_InitStructure.CAN_Mode = CAN_Mode_Normal;
CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
CAN_InitStructure.CAN_BS1 = CAN_BS1_10tq; //1--16
CAN_InitStructure.CAN_BS2 = CAN_BS2_7tq; //1--8
CAN_InitStructure.CAN_Prescaler = 4;//8 波特率=Fpclk1/(sjw+bs1+bs2)/pre
////(pclk1/((1+8+7)*16)) = 36Mhz/16/4 = 500Kbits
//CAN_Init(&CAN_InitStructure);
/*Initializes the CAN1 and CAN2 */
CAN_Init(CAN1, &CAN_InitStructure);
/* CAN cell init */
CAN_InitStructure.CAN_TTCM = DISABLE; //禁止时间触发通信模式
CAN_InitStructure.CAN_ABOM = DISABLE;
CAN_InitStructure.CAN_AWUM = DISABLE;
CAN_InitStructure.CAN_NART = DISABLE;
//CAN报文只被发送1次，不管发送的结果如何（成功、出错或仲裁丢失）
CAN_InitStructure.CAN_RFLM = DISABLE;
CAN_InitStructure.CAN_TXFP = DISABLE;
CAN_InitStructure.CAN_Mode = CAN_Mode_Normal;
CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
CAN_InitStructure.CAN_BS1 = CAN_BS1_10tq; //1--16
CAN_InitStructure.CAN_BS2 = CAN_BS2_7tq; //1--8
CAN_InitStructure.CAN_Prescaler =4;//4:500k//8 :250K//16:125K 波特率=Fpclk1/(sjw+bs1+bs2)/pre
////(pclk1/((1+8+7)*16)) = 36Mhz/16/4= 500Kbits
CAN_Init(CAN2, &CAN_InitStructure);
#if 1
CAN_FilterInitStructure.CAN_FilterNumber = 1; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_Light_Mode_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow =AUD_A4L_CAN_Lightness_And_CD_ONOFF_STD_ID << 5; //
//CAN_FilterInitStructure.CAN_FilterMaskIdHigh = CAN_ID_STD;
//CAN_FilterInitStructure.CAN_FilterMaskIdLow = CAN_ID_STD;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 2; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = ((AUD_A4L_CAN_Key_Control_Knob_EXT_ID << 3)>>16&0xffff);
CAN_FilterInitStructure.CAN_FilterIdLow = ((AUD_A4L_CAN_Key_Control_Knob_EXT_ID<<3)&0xffff)|CAN_ID_EXT; //
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
/*************************************************************
CAN2 接收
*************************************************************/
CAN_FilterInitStructure.CAN_FilterNumber = 14; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = ((AUD_A4L_CAN_RADA_EXT_ID << 3)>>16&0xffff);
CAN_FilterInitStructure.CAN_FilterIdLow = ((AUD_A4L_CAN_RADA_EXT_ID<<3)&0xffff)|CAN_ID_EXT; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = ((AUD_A4L_CAN_Media_Statu_EXT_ID<<3)>>16)&0xffff;
CAN_FilterInitStructure.CAN_FilterMaskIdLow = ((AUD_A4L_CAN_Media_Statu_EXT_ID<<3)&0xffff)|CAN_ID_EXT;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 15; //选择过滤器7
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;
CAN_FilterInitStructure.CAN_FilterIdHigh = ((AUD_A4L_CAN_Time_EXT_ID << 3)>>16)&0xffff;
CAN_FilterInitStructure.CAN_FilterIdLow = ((AUD_A4L_CAN_Time_EXT_ID << 3)&0xffff)|CAN_ID_EXT; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = ((AUD_A4L_CAN_Audio_Synchronous_EXT_ID << 3)>>16&0xffff);
CAN_FilterInitStructure.CAN_FilterMaskIdLow = ((AUD_A4L_CAN_Audio_Synchronous_EXT_ID<<3)&0xffff)|CAN_ID_EXT;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 16; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = ((AUD_A4L_CAN_Key_Control_Knob_EXT_ID << 3)>>16&0xffff);
CAN_FilterInitStructure.CAN_FilterIdLow = ((AUD_A4L_CAN_Key_Control_Knob_EXT_ID<<3)&0xffff)|CAN_ID_EXT; //
//CAN_FilterInitStructure.CAN_FilterMaskIdHigh =CAN_ID_EXT;
//CAN_FilterInitStructure.CAN_FilterMaskIdLow = CAN_ID_EXT;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 17; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = ((AUD_A4L_CAN_MUTE_STATUS_EXT_ID << 3)>>16&0xffff);
CAN_FilterInitStructure.CAN_FilterIdLow = ((AUD_A4L_CAN_MUTE_STATUS_EXT_ID<<3)&0xffff)|CAN_ID_EXT; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh =((AUD_A4L_CAN_BL_PHONE_NUM_SHOW_EXT_ID<<3)>>16&0XFFFF);
CAN_FilterInitStructure.CAN_FilterMaskIdLow = ((AUD_A4L_CAN_BL_PHONE_NUM_SHOW_EXT_ID<<3)&0XFFFF)|CAN_ID_EXT;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 18; //选择过滤器7
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_RADA_ONOFF_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow = AUD_A4L_CAN_HandBrake_STD_ID << 5; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = AUD_A4L_CAN_STEER_KEY_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterMaskIdLow = AUD_A4L_CAN_Turn_Angle_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 19; //选择过滤器7
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_Gears_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow = AUD_A4L_CAN_EngineSpeed_STD_ID << 5; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = AUD_A4L_CAN_Speed_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterMaskIdLow = AUD_A4L_CAN_Car_Front_Hood_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 20; //选择过滤器7
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_Infrared_Lock_Car_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow = AUD_A4L_CAN_Door_Rear_L_STD_ID << 5; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = AUD_A4L_CAN_Door_Rear_R_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterMaskIdLow = AUD_A4L_CAN_Door_Front_L_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 21; //选择过滤器7
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_Door_Front_R_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow = AUD_A4L_CAN_Door_Infor_STD_ID << 5; //
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = AUD_A4L_CAN_MileageRemain_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterMaskIdLow = AUD_A4L_CAN_Engine_Coolant_Temp_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 22; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_16bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_SafeBelt_Statu_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow =AUD_A4L_CAN_Turn_Light_LR_Statu_STD_ID << 5;
//CAN_FilterInitStructure.CAN_FilterMaskIdHigh =CAN_ID_STD;
//CAN_FilterInitStructure.CAN_FilterMaskIdLow =CAN_ID_STD;
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
CAN_FilterInitStructure.CAN_FilterNumber = 23; //选择过滤器0~13 for one can register
CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdList;//IdList mode or IdMask mode
CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;//16bits or 32bits
CAN_FilterInitStructure.CAN_FilterIdHigh = AUD_A4L_CAN_Oil_Mass_Outdoor_Temp_STD_ID << 5;
CAN_FilterInitStructure.CAN_FilterIdLow = CAN_ID_STD; //
CAN_FilterInitStructure.CAN_FilterFIFOAssignment = CAN_FIFO0; //选择FIFO0
CAN_FilterInitStructure.CAN_FilterActivation = ENABLE; //使能过滤器
CAN_FilterInit(&CAN_FilterInitStructure); //进入初始化函数
#endif
CAN_SlaveStartBank(13);//Miller
//-------------------------------------------------------------
/* CAN FIFO0 message pending interrupt enable */
CAN_ITConfig(CAN1, CAN_IT_FMP0 | CAN_IT_FF0, ENABLE);
/* CAN FIFO0 message pending interrupt enable */
CAN_ITConfig(CAN2, CAN_IT_FMP0 | CAN_IT_FF0, ENABLE);
}
对于双CAN STM32芯片，如果sFilterConfig.BankNumber=0，则所有过滤器组分配给CAN2使用，CAN1没得用。若sFilterConfig.BankNumber=27，则所有过滤器组分配给CAN1使用，CAN2就没得用了。
具体结合到本案例，客户代码里对CAN1、CAN2的过滤器进行配置时，当前过滤器组始终为0，即sFilterConfig.FilterNumber=0，而分配给CAN2的过滤器组又是从BANK 14开始的，即sFilterConfig.BankNumber = 14。
这样配置的话，CAN1接收，CAN2发的确不会有问题。反过来，CAN1发送，CAN2接收就会有问题。因为他一方面只是将Filter BANK 14到27分配给CAN2，同时又选择Filter BANK 0来配置CAN2的接收滤波器。所以要想CAN1发送，CAN2接收正常，其它参数不动的话，为CAN2配置滤波器时选择的过滤器组【Filter BANK】至少为14才可以，即sFilterConfig.FilterNumber=14。
案例2:在STM32双CAN产品中，CAN2不能进行接收，发送没问题。
这个问题经常有人碰到。很多情况是因为用户没有开启CAN1，或者在配置滤波器时，不是使用CAN1作为主体，而选择了CAN2。对于STM32双CAN芯片，CAN专用SRAM的访问以及对外来数据的滤波接收功能统一通过CAN1行使。因此，CAN1被称作为Master,CAN2被称作为Slave.换言之，CAN2对专用SRAM的访问和对信息滤波接收须借助CAN1来实现和管理。
顺便提下，这里说的MASTER CAN1和 SLAVE CAN2是从芯片内部资源管理职能而言的，并非针对CAN节点通信而言，否则就让人犯迷糊了。毕竟CAN通信并没有主从的说法。打个比方，就像你和某人一组共用一批设备各自做自己的课题，对方为组长。原则上这些设备共用，但由组长管理。你需要使用某些设备时需对方的协助与支持，至于你到底做什么，对方不干涉。反过来，组长需要使用那些设备时就不需要你的支持和协助，它自行使用和管理。
在使用STM32Cube库配置CAN2的过滤器时，早期版本在做CAN2的过滤器配置使用如下函数将CanHandle配置为CAN2时会有问题，须改用CAN1。不过后来的版本将这点做了修正。即使此为CAN2，在具体配置过滤器时的函数里还是会用CAN1去配置，详细可以查看该函数代码。【记得尽量使用最新版本库或手册】
HAL_CAN_ConfigFilter(&CanHandle,&sFilterConfig)
好，回到标题提到的关于STM32 CAN应用中的几个术语，过滤器组、过滤器、过滤器编号、过滤器索引。
过滤器组【filter bank】，是配置过滤器的原始资源，由2个32位寄存器组成。单CAN芯片有14个过滤器组，双CAN芯片有28个过滤器组，过滤器组编号由硬件拟定。一个过滤器组根据不同的过滤器模式【过滤方式和过滤器宽度】可配置1-4个过滤器。显然，过滤器组并不等同于过滤器。就好像说渔网的编制线材不等同于渔网一样的道理。过滤器组经过适当的配置后才能形成对信息具有过滤作用的过滤器。
做过滤器配置时，首先要选择过滤器组，然后配置过滤器的模式及宽度、并将配置的过滤器组与接收FIFO关联、激活当前的过滤器组。
在对过滤器组进行配置生成过滤器时，各个过滤器都被硬件自动编号，使得每个过滤器都有个编号【Filter Number】。CAN有两个FIFO,即FIFO0/FIFO1.这里有两套过滤器编号，即关联到FIFO0的过滤器与关联到FIFO1的过滤器分别各自从0开始依次编号。
表一、关联到FIFO0/FIFO1的过滤器编号示例
关联到FIFO里的过滤器组的过滤器的编号原则：
先依据过滤器组的编号大小做基本排序，再按照组内过滤模式及过滤器数量排序编号，可以参照表一、表二协助理解。
表二、过滤器组的配置及内部过滤器编号顺序
简单点讲，过滤器编号就是关联到各FIFO里的过滤器的序号，而且过滤器的编号跟过滤器组是否激活无关，只要配置且关联到FIFO就行。那过滤器匹配索引又是什么呢？
我们知道，一旦外来信息通过过滤器就会存放到相应的FIFO里，然后通过应用程序从FIFO中读取信息数据到SRAM。为了读取FIFO里的数据及进行存储，往往先要识别信息标识符，然后根据不同标识符将信息数据放到相应位置。不过，以信息标识符为标准来进行判别以及相应的存储访问，这个过程效率就不高。为此，CAN控制器就提供了过滤器匹配索引值【Filter Match Index】这个东西。
当外来信息通过过滤器后存储信息到FIFO的邮箱时，硬件自动将相应的过滤器编号写入FIFO邮箱内相关寄存器的过滤器匹配索引值【FMI】。所以，本质上讲过滤器匹配索引值跟过滤器编号是同一个数据，但代表的意义不一样。FMI表示本信息是经过哪个编号的过滤器匹配过滤而来。通过FMI可以快速找到相应的报文信息。
有了FMI,我们可以利用它作为数组序列直接访问相应的目的信息数据，或者拿收到的报文邮箱里的FMI跟所期望的数值比较来对信息筛选分类等。比如，考生除了名字外，一般都有准考证号。当考完试后，准考证可作为查分索引。如果没有这个准考证号，可能就得敲入考点、学生名字等多个身份信息，但效率就差了很多。
根据过滤器的配置与过滤规则，可能会出现一个外来信息可以通过多个过滤器的情况。这时FMI的值到底取哪一个过滤器的编号呢？这里就根据过滤器优先级原则来定。有如下三条规则：
1、32位过滤器优先于16位过滤器。
2、当过滤器同等宽度时，标识符列表模式优先于标识符屏蔽模式。
3、当过滤器模式及宽度一样时，低过滤器编号优先于高过滤器编号。
假设我们要接收多个ID：0x7e9,0x1800f001,前面为标准ID，后面为扩展ID，要同时能接收这两个ID，那么该如何设置这个过滤器呢?
1. CAN_FilterInitTypeDef CAN_FilterInitStructure;
2. U16 std_id =0x7e9;
3. U32 ext_id =0x1800f001;
4. U32 mask =0;
5.
6. CAN_FilterInit(&CAN_FilterInitStructure); //初始化CAN_FilterInitStructrue结构体变量
7. CAN_FilterInitStructure.CAN_FilterNumber=0; //设置过滤器组0，范围为0~13
8. CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask; //设置过滤器组0为屏蔽模式
9. CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit; //设置过滤器组0位宽为32位
10.
11. //标识位寄存器的设置
12. //ext_id<<3对齐，见上图9，再>>16取高16位
13. CAN_FilterInitStructure.CAN_FilterIdHigh=（(ext_id<<3) >>16) &0xffff; //设置标识符寄存器高字节。
14. CAN_FilterInitStructure.CAN_FilterIdLow=(U16)(ext_id<<3) | CAN_ID_EXT; //设置标识符寄存器低字节
15. //这里也可以这样设置
16. //CAN_FilterInitStructure.CAN_FilterIdHigh=std_id<<5; //设置标识符寄存器高字节.这里为什么是左移5位呢？从上图可以看出，CAN_FilterIdHigh包含的是STD[0~10]和EXID[13~17],标准CAN ID本身是不包含扩展ID数据，因此为了要将标准CAN ID放入此寄存器，标准CAN ID首先应左移5位后才能对齐.
17. //CAN_FilterInitStructure.CAN_FilterIdLow=0|CAN_ID_EXT; //设置标识符寄存器低字节,这里也可以设置为CAN_ID_STD
18.
19. //屏蔽寄存器的设置
20. //这里的思路是先将标准CAN ID和扩展CAN ID对应的ID值先异或后取反，为什么？异或是为了找出两个CAN ID有哪些位是相同的，是相同的位则说明需要关心，需要关心的位对应的屏蔽码位应该设置为1，因此需要取反一下。最后再整体左移3位。
21. mask =(std_id<<18);//这里为什么左移18位？因为从ISO11898中可以看出，标准CAN ID占ID18~ID28，为了与CAN_FilterIdHigh对齐，应左移2位，接着为了与扩展CAN对应，还应该再左移16位，因此，总共应左移2+16＝18位。也可以用另一个方式来理解：直接看Mapping的内容，发现STDID相对EXID[0]偏移了18位,因此左移18位.
22. mask ^=ext_id;//将对齐后的标准CAN与扩展CAN异或后取反
23. mask =~mask;
24. mask <<=3;//再整体左移3位
25. mask |=0x02; //只接收数据帧，不接收远程帧
26. CAN_FilterInitStructure.CAN_FilterMaskIdHigh=(mask>>16)&0xffff; //设置屏蔽寄存器高字节
27. CAN_FilterInitStructure.CAN_FilterMaskIdLow=mask&0xffff; //设置屏蔽寄存器低字节
28.
29. CAN_FilterInitStructure.CAN_FilterFIFOAssignment=CAN_FIFO0; //此过滤器组关联到接收FIFO0
30. CAN_FilterInitStructure.CAN_FilterActivation=ENABLE; //激活此过滤器组
31. CAN_FilterInit(&CAN_FilterInitStructure); //设置过滤器
can：filter总结：1.两组can,can1与can2有0~27组过滤器；
2.配置成32位掩码过滤器有28组，配置成16位掩码过滤器有56组；
3.配置成32位列表过滤器有56组，配置成16位列表过滤器有112组过滤器。