Problems with UART on STMF4 Discovery Board

Question

I have some problems with UART comunication. My platform is STM32f4 Discovery Board with STM32f407VG.

First my system setup:

void clock_setup(void)
{
    RCC->PLLCFGR = (uint32_t)0x27412A04;
    RCC->CFGR = (uint32_t)0x00081000;
    RCC->CR |= (uint32_t)0x00010000;
    while((RCC->CR & 0x00020000) != 0x00020000);
    RCC->CR |= (uint32_t)0x01000000;    
    while((RCC->CR & 0x02000000) != 0x02000000);
    FLASH->ACR = (uint32_t)0x00000702;
    RCC->CFGR |= (uint32_t)0x00000002;
    while(!(RCC->CFGR & 0x00000008));
}
void system_setup(void)
{
    SCB->CPACR |= 0x00f00000; //fpu can be configured
    clock_setup();
}

Main and button interrupt handler:

int main(void)
{
    int i = 0;
    __enable_irq();
    NVIC_SetPriority(EXTI0_IRQn,0x31);
    NVIC_EnableIRQ(EXTI0_IRQn);
    SYSCFG->EXTICR[0] = 1;
    EXTI->IMR = 0x00000001;
    EXTI->RTSR = 0x00000001; //rising edge on
    EXTI->FTSR = 0x00000000; //falling edge off
    RCC->AHB1ENR |= (uint32_t)0x00000009;
    GPIOD->MODER = (uint32_t)0x55000000;
    GPIOD->OTYPER = (uint32_t)0x0000000;

    USART1_Config();

    while(1){
    }
    return 1;
}
void EXTI0_IRQHandler(void)
{
    if(EXTI->PR & (1<<0))
    {
        USART1_puts("Test\n");
        enableBlink = !enableBlink;
    }
    EXTI->PR |= (1<<0);
}

USART configuration and functions:

void USART1_puts(volatile char* s)
{
    while(*s)
    {
        while(!(USART1->SR & 0x00000040)){
        }
        USART_SendData(USART1,*s);
        *s++;
    }
}
void USART1_Config(void)
{
    USART_InitTypeDef USART_InitStruct;
    GPIO_InitTypeDef GPIO_InitStruct, GPIO_InitStruct2;
    NVIC_InitTypeDef NVIC_InitStruct;

        /* Enable clocks */
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;//GPIO_PuPd_UP;
    GPIO_Init(GPIOA,&GPIO_InitStruct);
    GPIO_PinAFConfig(GPIOA,GPIO_PinSource9,GPIO_AF_USART1);
    GPIO_PinAFConfig(GPIOA,GPIO_PinSource10,GPIO_AF_USART1);

    USART_InitStruct.USART_WordLength = USART_WordLength_8b;
    USART_InitStruct.USART_BaudRate = 9600;
    USART_InitStruct.USART_StopBits = USART_StopBits_1;
    USART_InitStruct.USART_Parity = USART_Parity_No;
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;                                                                       
    USART_InitStruct.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;
    USART_Init(USART1,&USART_InitStruct);
    USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);

    NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);

    USART_Cmd(USART1,ENABLE);
}
void USART1_IRQHandler(void)
{
    int i = 0;
    if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
    {
            static uint8_t cnt = 0;
        char t = USART_ReceiveData(USART1);
        USART1_putch(t);
        if((t!='n')&&(cnt < MAX_STRLEN))
        {
            received_string[cnt] = t;
            cnt++;
        }
        else
        {
            cnt = 0;
            USART1_puts(received_string);
            for (i = 0; i <= MAX_STRLEN+1; i++)         // flush buffer
            received_string[i] = '\0'; 
        }
    }
}

First problem is when I send Test to terminal it shows ˙ţ‡đ˙ţř Second problem when USART interrupt is fired it reads only one char from input. During debug ASCII code is the same as send from terminal. But the rest of string from terminal is not readed. And USART1_putch function gives to terminal different char as input.

What can be the problem? Maybe it is something connected with clocks? Code is basing mainly on this tutorial.

Answer 1

When working with the STM32F4-Discovery board (or any similar board), you have to make sure that the pins of the microcontroller you want to use are not already in use by another component on the board. The user manual for the STM32F4-Discovery has table 5, which shows you exactly which IO pins are in use, and which are free. If they are not free, you may still be able to use them, but you will need to check on the schematic how exactly they are connected to other components, and how those components might affect the desired operation. In your case, pins PA9 and PA10 are not free (they are connected to the USB port and a LED), which most likely interferes with the serial communication.