Question

I am having issues trying to use the UART (USART1) on my F4Discovery board (based on an STM32F407). I am pretty new to STM32 and Keil (the IDE I am using). Here’s my code:

#include "stm32f4_discovery.h"
#include "stm32f4xx_usart.h"
#include "stm32f4xx.h"

void usartSetup(void);
void USART_PutChar(uint8_t ch);

int main (void) {
    usartSetup();

    USART_PutChar(0);   //I realise this won't send a 0
    USART_PutChar(8);   //I realise this won't send an 8
    USART_PutChar(255);   //I realise this won't send a 255

    while (1) {
        //loop forever
    }
}

void usartSetup (void) {
    USART_InitTypeDef USART_InitStructure;
    //USART_StructInit(&USART_InitStructure);
    USART_InitStructure.USART_BaudRate = 9600;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl =  USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStructure);
    USART_Cmd(USART1, ENABLE);
}

void USART_PutChar(uint8_t ch) {
    USART_SendData(USART1, (uint16_t) 0x49);
    while(USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);
    USART_SendData(USART1, (uint16_t) 0x49);
}

I’d be very grateful if someone could help. It never sends the 0x49 out of the UART1 TX (have checked pin PA9 and PB6) and then gets endlessly stuck on the while(USART_GetFlagStatus…). I am observing using the Keil debugger and see it get stuck in the while.

I am including the stm32f4xx_usart.c driver into the project.

Thanks!

Answer 1

You haven’t configured output pins to use USART and clocks. If you use USART1 or USART6, you will have to set APB2 clock (highspeed) against APB1 (lowspeed)

/* For output on GPIOA */
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2);

/* Output pins configuration, change M and N index! */
GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_N | GPIO_Pin_M;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; // Push - pull
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOA, &GPIO_InitStructure);

GPIO_PinAFConfig(GPIOA, GPIO_PinSourceN, GPIO_AF_USART2);
GPIO_PinAFConfig(GPIOA, GPIO_PinSourceM, GPIO_AF_USART2);