这两天玩了一下stm32f042的can，但是折腾了2个晚上，还是没有进展。我知道stm32f042F6P6 ssop20封装的pin17,pin18默认是PA9,PA10的功能，如果想使用PA11和PA12，需要进行端口映射。这样的话，我直接就用了下面的代码，进行端口映射，

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1. SYSCFG_MemoryRemapConfig(SYSCFG_CFGR1_PA11_PA12_RMP);

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结果Can总线一直没有波形出来。使用回环模式调试，总线上一直没有波形。
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/ W; ~1 J$ s4 d  i0 N$ l由于CAN的PA11和PA12和串口1的PA9和PA10是复用的，没有第一时间使用串口进行调试。今天晚上下班将usart2飞线飞出来了。使能断言后，发现下面的断言错误。

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1. DEBUG [D] main:94 hello armwind
   
2. DEBUG [D] assert_failed:94<div> …/Lib/STM32F0xx_StdPeriph_Driver/src/stm32f0xx_syscfg.c,line:119</div>

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查看源码发现，断言表明，这个方法只能映射系统mem.

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1. void SYSCFG_MemoryRemapConfig(uint32_t SYSCFG_MemoryRemap)
   
2. {
   
3.   uint32_t tmpctrl = 0;
   
4. 
   
5.   /* Check the parameter */
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6.   assert_param(IS_SYSCFG_MEMORY_REMAP(SYSCFG_MemoryRemap));
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7. 
   
8.   /* Get CFGR1 register value */
   
9.   tmpctrl = SYSCFG->CFGR1;
   
10. 
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11.   /* Clear MEM_MODE bits */
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12.   tmpctrl &= (uint32_t) (~SYSCFG_CFGR1_MEM_MODE);
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13. 
    
14.   /* Set the new MEM_MODE bits value */
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15.   tmpctrl |= (uint32_t) SYSCFG_MemoryRemap;
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16. 
    
17.   /* Set CFGR1 register with the new memory remap configuration */
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18.   SYSCFG->CFGR1 = tmpctrl;
    
19. }
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20. 
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21. //宏定义很明显
    
22. #define IS_SYSCFG_MEMORY_REMAP(REMAP) (((REMAP) == SYSCFG_MemoryRemap_Flash) || \
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23.                                        ((REMAP) == SYSCFG_MemoryRemap_SystemMemory) || \
    
24.                                        ((REMAP) == SYSCFG_MemoryRemap_SRAM))

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+ \+ B; c. ~4 o所以使用下面代码即可map成功
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1. //不要覆盖掉系统原始的配置
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2. SYSCFG->CFGR1 = SYSCFG->CFGR1 | SYSCFG_CFGR1_PA11_PA12_RMP;

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完整的Can初始化代码

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1. void can_init(void)
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2. {
   
3.   GPIO_InitTypeDef  GPIO_InitStructure;
   
4.   NVIC_InitTypeDef  NVIC_InitStructure;
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5.   CAN_InitTypeDef        CAN_InitStructure;
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6.   CAN_FilterInitTypeDef  CAN_FilterInitStructure;
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7. 
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8.   RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);
   
9.   SYSCFG->CFGR1 = SYSCFG->CFGR1 | SYSCFG_CFGR1_PA11_PA12_RMP;
   
10. 
    
11.   //这里一定要先映射GPIO
    
12.   /* Enable GPIO clock */
    
13.   RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
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14.   /* Connect CAN pins to AF7 */
    
15.   /* CAN GPIOs configuration **************************************************/
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16.   GPIO_PinAFConfig(GPIOA, GPIO_PinSource11, GPIO_AF_4);
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17.   GPIO_PinAFConfig(GPIOA, GPIO_PinSource12, GPIO_AF_4);
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18. 
    
19.   /* Configure CAN RX and TX pins */
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20.   GPIO_InitStructure.GPIO_Pin = GPIO_PinSource11 | GPIO_PinSource12;
    
21.   GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
    
22.   GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
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23.   GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    
24.   GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_UP;
    
25.   GPIO_Init(GPIOA, &GPIO_InitStructure);
    
26. 
    
27.   /* NVIC configuration *******************************************************/
    
28.   NVIC_InitStructure.NVIC_IRQChannel = CEC_CAN_IRQn;
    
29.   NVIC_InitStructure.NVIC_IRQChannelPriority = 0x0;
    
30.   NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    
31.   NVIC_Init(&NVIC_InitStructure);
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32. 
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33.   /* CAN configuration ********************************************************/
    
34.   /* Enable CAN clock */
    
35.   RCC_APB1PeriphClockCmd(RCC_APB1Periph_CAN, ENABLE);
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36. 
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37.   /* CAN register init */
    
38.   CAN_DeInit(CAN);
    
39.   CAN_StructInit(&CAN_InitStructure);
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40. 
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41.   /* CAN cell init */
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42.   CAN_InitStructure.CAN_TTCM = DISABLE;
    
43.   CAN_InitStructure.CAN_ABOM = DISABLE;
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44.   CAN_InitStructure.CAN_AWUM = DISABLE;
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45.   CAN_InitStructure.CAN_NART = DISABLE;
    
46.   CAN_InitStructure.CAN_RFLM = DISABLE;
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47.   CAN_InitStructure.CAN_TXFP = DISABLE;
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48.   CAN_InitStructure.CAN_Mode = CAN_Mode_Normal;
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49.   //CAN_InitStructure.CAN_Mode = CAN_Mode_LoopBack;
    
50.   CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
    
51. 
    
52.   //200k的配置
    
53.   //48M/12/(CAN_SJW_1tq + CAN_BS1_4tq+CAN_BS2_5tq) == 200k
    
54.   /* CAN Baudrate = 1MBps (CAN clocked at 36 MHz) */
    
55.   CAN_InitStructure.CAN_BS1 = CAN_BS1_4tq;
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56.   CAN_InitStructure.CAN_BS2 = CAN_BS2_5tq;
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57.   CAN_InitStructure.CAN_Prescaler = 12;
    
58.   CAN_Init(CAN, &CAN_InitStructure);
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59. 
    
60.   /* CAN filter init */
    
61.   CAN_FilterInitStructure.CAN_FilterNumber = 1;
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62.   CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdMask;
    
63.   CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;
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64.   CAN_FilterInitStructure.CAN_FilterIdHigh = 0x0000;
    
65.   CAN_FilterInitStructure.CAN_FilterIdLow = 0x0000;
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66.   CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0x0000;
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67.   CAN_FilterInitStructure.CAN_FilterMaskIdLow = 0x0000;
    
68.   CAN_FilterInitStructure.CAN_FilterFIFOAssignment = 0;
    
69.   CAN_FilterInitStructure.CAN_FilterActivation = ENABLE;
    
70.   CAN_FilterInit(&CAN_FilterInitStructure);
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71.   /* Transmit Structure preparation */
    
72. 
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73.   /* Enable FIFO 0 message pending Interrupt */
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74.   CAN_ITConfig(CAN, CAN_IT_FMP0, ENABLE);
    
75. }
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76. 
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77. 
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