USART with STM32F373VCt6

Question

I'm new here. I've just started learning STM32F373 with STM32F373VCT6. I use CMSIS to configure UART1. that seems there are no any error with my code. But when I use PL2303 to convert serial-usb for connecting with PC. I don't receive anything.

Here is my code. Can anyone help me to find your mistake?

/* Includes ------------------------------------------------------------------*/
#include "stm32f37x.h"
#include"main.h"
uint8_t ledVal = 0; 
static __IO uint32_t TimingDelay;
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
#define BSRR_VAL 0x0003
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
GPIO_InitTypeDef        GPIO_InitStructure;
/* Private function prototypes -----------------------------------------------*/
uint8_t SendChar (uint8_t ch);
void GPIO_Config(void);
void USART1_Config(void);
uint8_t GetChar (void);
int main(void)
{
  /*!< At this stage the microcontroller clock setting is already configured, 
       this is done through SystemInit() function which is called from startup
       file (startup_stm32f37x.s) before to branch to application main.
       To reconfigure the default setting of SystemInit() function, refer to
       system_stm32f37x.c file
     */
    //SystemInit();
 /* GPIOC Periph clock enable */
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOC, ENABLE);

 /* Configure PC0 and PC1 in output pushpull mode */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_2MHz;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOC, &GPIO_InitStructure);
    GPIO_Config();
    USART1_Config();
    if (SysTick_Config(SystemCoreClock / 1000))
                while (1);


  while (1)
  {
    /* Set PC0 and PC1 */
    GPIO_WriteBit(GPIOC , GPIO_Pin_13 , (ledVal) ? Bit_SET : Bit_RESET);
        ledVal = 1 - ledVal;
        SendChar('f');
        Delay(250);

  }
}
#ifdef  USE_FULL_ASSERT

/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t* file, uint32_t line)
{ 
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */

  /* Infinite loop */
  while (1)
  {
  }
}
#endif

/**
  * @}
  */

/**
  * @}
  */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

void GPIO_Config(void) {
    // PC4 configuration (TX)
    RCC->AHBENR |= 1 << 19; // enable GPIOC clock
    GPIOC->MODER |= 2 << (4*2); // GPIO_Mode_AF
    GPIOC->OTYPER |= 1 << (4*1); // GPIO_OType_OD
    GPIOC->OSPEEDR |= 3 << (4*2); // GPIO_Speed_50MHz
    GPIOC->PUPDR &= ~(3 << (4*2)); // GPIO_PuPd_NOPULL
    GPIOC->AFR[0] |= 7 << (4*4); // AF7
    // PC5 configuration (RX)
    GPIOC->MODER |= 2 << (5*2); // GPIO_Mode_AF
    GPIOC->AFR[0] |= 7 << (5*4); // AF7
}
/* Configuring USART1 */
void USART1_Config(void)
{
    RCC->APB2ENR |= RCC_APB2ENR_USART1EN|RCC_APB2ENR_SYSCFGEN; // Enable USART1 clock
    USART1->BRR = 72000000/115200;
    USART1->CR1 &= ~USART_CR1_OVER8; // Oversampling mode = 16
    USART1->CR1 &= ~USART_CR1_M; // Word length = 8 bits
    USART1->CR2 &= ~(USART_CR2_STOP_1 | USART_CR2_STOP_0); // one stop bit
    USART1->CR1 &= ~USART_CR1_PCE; // No parity
    USART1->CR1 |= USART_CR1_UE; // USART enable
    USART1->CR1 |= USART_CR1_RE; // Receiver enable
    USART1->CR1 |= USART_CR1_TE; // Transmitter enable
}
uint8_t SendChar (uint8_t ch)
{
    while (!(USART1->ISR & USART_ISR_TXE));
    USART1->TDR = (ch & 0xFF);
    return (ch);
}
uint8_t GetChar (void)
{ 
    while (!(USART1->ISR & USART_ISR_RXNE));
    return ((uint8_t)(USART1->RDR & 0xFF));
}
/* Delay fuction */
void Delay(__IO uint32_t nTime)
{
    TimingDelay = nTime;
    while(TimingDelay != 0);
}
/* Decrement */
void TimingDelay_Decrement(void)
{
    if (TimingDelay != 0x00)
    TimingDelay --;
}

Answer 1

Delays after RCC operations are missing

The errata for STM32F373 series says,

2.1.2 Delay after an RCC peripheral clock enabling

Description A delay between an RCC peripheral clock enable and the effective peripheral enabling should be taken into account in order to manage the peripheral read/write from/to registers. This delay depends on the peripheral mapping.

If peripheral is mapped on AHB: the delay is 2 AHB clock cycles after the clock enable bit is set on the hardware register.

If peripheral is mapped on APB: the delay is 2 APB clock cycles after the clock enable bit is set on the hardware register.

Workarounds

1. Enable the peripheral clock sometimes before the peripheral read/write register is required.

2. For AHB peripheral, insert two dummy read to the peripheral register.

3. For APB peripheral, insert a dummy read to the peripheral register.

Without this delay, a read (or two) immediately following the RCC enable operation could return 0 regardless of the register value, or the first two writes could be ignored by the peripheral.

The library function RCC_AHBPeriphClockCmd() may already include this delay, but check the Stdperiph sources to be sure.

I usually group RCC accesses at the start if possible, starting with the peripheral I'm going to use first.

RCC->AHBENR |= 1 << 19; // enable GPIOC clock              // (1)
RCC->APB2ENR |= RCC_APB2ENR_USART1EN|RCC_APB2ENR_SYSCFGEN; // (2)
GPIOC->MODER = whatever;                                   // (3)
// ...
USART1->BRR = divisor;

This way, the read-modify-write operation in (2) would introduce a sufficient delay between enabling GPIOC (1) and using it (3).