c - USART3初始化STM32F103RB

Question

我是一个使用STM芯片的初学者，我有一个项目，我必须在Uvision中使用所有三个USART终端。

我使用的是 STM32F103RB 芯片，并且我已经使前两个 USART_init 函数正常工作，但由于某种原因我无法使第三个函数正常工作。我真的很感激任何帮助这是我的 USART_init 函数:

/*----------------------------------------------------------------------------
  Initialize UART pins, Baudrate
 *----------------------------------------------------------------------------*/
void USART1_Init (void) {
  int i;

  RCC->APB2ENR |=  (   1UL <<  0);        /* enable clock Alternate Function  */
  AFIO->MAPR   &= ~(   1UL <<  2);        /* clear USART1 remap               */

  RCC->APB2ENR |=  (   1UL <<  2);        /* enable GPIOA clock               */
  GPIOA->CRH   &= ~(0xFFUL <<  4);        /* clear PA9, PA10                  */
  GPIOA->CRH   |=  (0x0BUL <<  4);        /* USART1 Tx (PA9) output push-pull */
  GPIOA->CRH   |=  (0x04UL <<  8);        /* USART1 Rx (PA10) input floating  */

  RCC->APB2ENR |=  (   1UL << 14);        /* enable USART#1 clock             */

  USART1->BRR   = 0x0271;                 /* 115200 baud @ PCLK2 72MHz        */
  USART1->CR1   = ((   1UL <<  2) |       /* enable RX                        */
                   (   1UL <<  3) |       /* enable TX                        */
                   (   0UL << 12) );      /* 1 start bit, 8 data bits         */
  USART1->CR2   = 0x0000;                 /* 1 stop bit                       */
  USART1->CR3   = 0x0000;                 /* no flow control                  */
  for (i = 0; i < 0x1000; i++) __NOP();   /* avoid unwanted output            */

  USART1->CR1  |= ((   1UL << 13) );      /* enable USART                     */
}

/*----------------------------------------------------------------------------
  Initialize UART2 pins, Baudrate
 *----------------------------------------------------------------------------*/
void USART2_Init (void) {

  RCC->APB2ENR |= 1;                                    // enable clock for AF
    AFIO->MAPR |= 1<<3;                                 // set USART2 remap
    RCC->APB2ENR |= 1<<5;                           // enable clock for GPIOD
    GPIOD->CRL &= ~(0xFF << 20);                // Clear PD5, PD6
    GPIOD->CRL |= (0x0B << 20);                 // USART2 Tx (PD5) output push-pull
    GPIOD->CRL |= (0x04 << 24);                 // USART2 Rx (PD6) input floating
    RCC->APB1ENR |= 1<<17;                          // enable clock for USART2
    USART2->BRR = 0x138;                                // set baudrate -115.2kB from 36MHz
    USART2->CR1 &= ~(1<<12);                        // force 8 data bits
    USART2->CR2 &= ~(3<<12);                        // force 1 stop bit
    USART2->CR3 &= ~(3<<8);                         // force no flow control
    USART2->CR1 &= ~(3<<9);                         // force no parity
    USART2->CR1 |= 3<<2;                                // RX, TX enable
    USART2->CR1 |= 1<<5;                                // Rx interrupts if required
    NVIC->ISER[1] = (1 << 6);                   // enable interrupts if required
    USART2->CR1 |= 1<<13;                           // USART enable
    
}

/*----------------------------------------------------------------------------
  Initialize UART3 pins, Baudrate
 *----------------------------------------------------------------------------*/
void USART3_Init (void) {

  RCC->APB2ENR |= 1;                                    // enable clock for AF
    AFIO->MAPR |= 1<<3;                                // set USART3 remap
    RCC->APB2ENR |= 1<<4;                               // enable clock for GPIOC
    
  GPIOC->CRH   &= ~(0xFFUL <<  4);        /* clear PC10, PC11                  */
    GPIOC->CRH   |=  (0x04UL <<  8);        /* USART3 Rx (PC10) input floating  */
  GPIOC->CRH   |=  (0x01UL <<  8);        /* USART3 Tx (PC11) output push-pull */
    RCC->APB1ENR |=  1<<20;                                 // enable clock for USART3
    
    USART3->BRR = 0x138;                                // set baudrate -115.2kB from 36MHz; USART3    
                                                    //should have the same baudrate as USART2
    USART3->CR1 &= ~(1<<12);                        // force 8 data bits
    USART3->CR2 &= ~(3<<12);                        // force 1 stop bit
    USART3->CR3 &= ~(3<<8);                         // force no flow control
    USART3->CR1 &= ~(3<<9);                         // force no parity
    USART3->CR1 |= 3<<2;                                // RX, TX enable
    USART3->CR1 |= 1<<5;                                // Rx interrupts if required
    NVIC->ISER[1] = (1 << 6);                   // enable interrupts if required
    USART3->CR1 |= 1<<13;                           // USART enable
    
}

Answer 1

USART3 初始化的第一行是错误的:-)

RCC->APB2ENR |= 1; // enable clock for AF

必须是(没有时钟，USART 无法工作)

RCC->APB1ENR |= (1<<18); // enable clock for USART

作为附加提示，不要将所有这些魔数(Magic Number)用于位。这更具可读性(并且所需的定义已在 CMSIS 中完成:

RCC->APB1ENR |= RCC_APB1ENR_USART3EN; // enable clock for USART