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I have been trying to get the usart working on the stm32f3 discovery board for a while. I am using a 3.3V FTDI basic from sparkfun for the purpose. So far, I haven't got a peep from the program.

The program is given below:

    /* Includes ------------------------------------------------------------------*/
#include <stm32f30x.h>
#include <stm32f30x_rcc.h>
#include <stm32f30x_rcc.c>
#include <stm32f30x_gpio.h>
#include <stm32f30x_gpio.c>
#include <stm32f30x_misc.h>
#include <stm32f30x_misc.c>
#include <stm32f30x_tim.h>
#include <stm32f30x_tim.c>
#include <stm32f30x_usart.h>
#include <stm32f30x_usart.c>
//#include <arm_math.h>

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
volatile int ms;

/* Private function prototypes -----------------------------------------------*/

/* Private functions ---------------------------------------------------------*/
void SysTick_Handler(void)
{
  ms++;
    if (ms>99){
        USART_SendData(USART1,'S');
        while(USART_GetFlagStatus(USART2,USART_FLAG_TXE)==RESET){}
        ms=0;
    }
}

/**
  * @brief  Main program.
  * @param  None
  * @retval None
  */
int main(void)
{
  GPIO_InitTypeDef GPIO_InitStruct;
    USART_InitTypeDef USART_InitStruct;

    /*GPIO configuration for indicator LED*/
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOE,ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_8;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;

    GPIO_Init(GPIOE,&GPIO_InitStruct);

    //Turn LED on
    GPIO_SetBits(GPIOE,GPIO_Pin_8);

    /*GPIO configuration for USART. PA2 = USART2_TX, PA3 = USART2_RX*/
    //Enable clock for GPIOA
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA,ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_2|GPIO_Pin_3;
    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_DOWN;

    GPIO_Init(GPIOA,&GPIO_InitStruct);

    //AF configuration
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_7);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_7);

    /*USART configuration*/
    USART_Cmd(USART2, ENABLE);

    USART_InitStruct.USART_BaudRate = 9600;
  USART_InitStruct.USART_WordLength = USART_WordLength_8b;
  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_Rx | USART_Mode_Tx;

  USART_Init(USART2, &USART_InitStruct);

    //Enable RXNE interrupt
    USART_ITConfig(USART2,USART_IT_RXNE,ENABLE);
    //Enable USART global interrupt
    NVIC_EnableIRQ(USART2_IRQn);

    if (SysTick_Config(SystemCoreClock / 1000))
  { 
    /* Capture error */ 
    while (1);
  }

  while (1)
  {

  }
}

void USART2_IRQHandler(void){
    /*RXNE handler*/
    if(USART_GetITStatus(USART2,USART_IT_RXNE) != RESET){
        /*If recieved 't', toggle LED, transmit 'T'*/
        if((char)USART_ReceiveData(USART2) == 't'){
            /*Toggle LED*/
            if (GPIO_ReadOutputDataBit(GPIOE,GPIO_Pin_8)){
                GPIO_ResetBits(GPIOE,GPIO_Pin_8);
            }
            else{
                GPIO_SetBits(GPIOE,GPIO_Pin_8);
            }

            /*USART_SendData(USART1,'T');
            while(USART_GetFlagStatus(USART2,USART_FLAG_TXE)==RESET){}*/
        }
    }
}

I am using the Keil uvision 5 IDE.

Thank you.

EDIT: The current code is given below:

/* Includes ------------------------------------------------------------------*/
#include <stm32f30x.h>
#include <stm32f30x_rcc.h>
#include <stm32f30x_rcc.c>
#include <stm32f30x_gpio.h>
#include <stm32f30x_gpio.c>
#include <stm32f30x_misc.h>
#include <stm32f30x_misc.c>
#include <stm32f30x_tim.h>
#include <stm32f30x_tim.c>
#include <stm32f30x_usart.h>
#include <stm32f30x_usart.c>
//#include <arm_math.h>

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
volatile int ms;

/* Private function prototypes -----------------------------------------------*/

/* Private functions ---------------------------------------------------------*/
void SysTick_Handler(void)
{
  ms++;
    if (ms>99){
        USART_SendData(USART1,'S');
        while(USART_GetFlagStatus(USART2,USART_FLAG_TXE)==RESET){};
        if (GPIO_ReadOutputDataBit(GPIOE,GPIO_Pin_12)){
                GPIO_ResetBits(GPIOE,GPIO_Pin_12);
        }
        else{
                GPIO_SetBits(GPIOE,GPIO_Pin_12);
        }
        ms=0;
    }
}

/**
  * @brief  Main program.
  * @param  None
  * @retval None
  */
int main(void)
{
  GPIO_InitTypeDef GPIO_InitStruct;
    USART_InitTypeDef USART_InitStruct;

    /*GPIO configuration for indicator LED*/
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOE,ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_8|GPIO_Pin_9|GPIO_Pin_10|GPIO_Pin_11|GPIO_Pin_12;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;

    GPIO_Init(GPIOE,&GPIO_InitStruct);

    //Turn LED on
    GPIO_SetBits(GPIOE,GPIO_Pin_8|GPIO_Pin_12);

    /*GPIO configuration for USART. PA2 = USART2_TX, PA3 = USART2_RX*/
    //Enable clock for GPIOA
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA,ENABLE);

    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_2|GPIO_Pin_3;
    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_DOWN;

    GPIO_Init(GPIOA,&GPIO_InitStruct);

    //AF configuration
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_7);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_7);

    /*USART configuration*/
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2,ENABLE);
    USART_Cmd(USART2, ENABLE);

    USART_InitStruct.USART_BaudRate = 9600;
  USART_InitStruct.USART_WordLength = USART_WordLength_8b;
  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_Rx | USART_Mode_Tx;

  USART_Init(USART2, &USART_InitStruct);

    //Enable RXNE interrupt
    USART_ITConfig(USART2,USART_IT_RXNE,ENABLE);
    GPIO_SetBits(GPIOE,GPIO_Pin_9);
    //Enable USART global interrupt
    NVIC_EnableIRQ(USART2_IRQn);
    GPIO_SetBits(GPIOE,GPIO_Pin_10);

    if (SysTick_Config(SystemCoreClock / 1000))
  { 
    /* Capture error */ 
    while (1);
  }
    GPIO_SetBits(GPIOE,GPIO_Pin_11);

  while (1)
  {

  }
}

void USART2_IRQHandler(void){
    /*RXNE handler*/
    if(USART_GetITStatus(USART2,USART_IT_RXNE) != RESET){
        /*If recieved 't', toggle LED, transmit 'T'*/
        if((char)USART_ReceiveData(USART2) == 't'){
            /*Toggle LED*/
            if (GPIO_ReadOutputDataBit(GPIOE,GPIO_Pin_8)){
                GPIO_ResetBits(GPIOE,GPIO_Pin_8);
            }
            else{
                GPIO_SetBits(GPIOE,GPIO_Pin_8);
            }

            /*USART_SendData(USART1,'T');
            while(USART_GetFlagStatus(USART2,USART_FLAG_TXE)==RESET){}*/
        }
    }
}

There is no response from the program at this time. (TX is constant at 3.3V, RX is at 0v).

UPDATE: I have tried using USART1 instead, and I still get no response. The other changes include moving the transmission part of the code to the while loop, and trying with GPIO_PuPd_UP, GPIO_PuPd_DOWN and GPIO_PuPd_NOPULL, with no result. Currently, when using USART2, the TX (PA2) is at a constant 3.3V, and RX(PA3) at 0v. On moving it to USART1, both(PC4,PC5) seem to be at a constant 3.3V.

UPDATE: The TX of the USART is working now, I had to enable the USART after initialising it, not before, as discussed here: https://community.st.com/thread/47271-usart-stm32f3-discovery

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9
  • 1
    \$\begingroup\$ What do you mean by "Haven't got a peep out of?" No receive interrupt? What does your scope say the signal looks like going into the Rx pin? We need a schematic too. If you're using Keil, you have a good debugger. Have you set a breakpoint at the end of your UART init to see whether the registers are set as you think they should be? \$\endgroup\$
    – DiBosco
    Feb 6, 2018 at 9:26
  • \$\begingroup\$ you havent enabled Peripheral clock for USART2 \$\endgroup\$
    – Abel Tom
    Feb 6, 2018 at 13:00
  • \$\begingroup\$ if my answer worked for you, could you please mark it as accepted. \$\endgroup\$
    – Abel Tom
    Feb 6, 2018 at 13:59
  • 2
    \$\begingroup\$ It seems a little odd that you are #includeing .c files along with the .h files. You should only have to include the .h file. \$\endgroup\$
    – Ron Beyer
    Feb 6, 2018 at 17:20
  • 1
    \$\begingroup\$ Yes, but the linker fails if I don't. I'm not sure why. \$\endgroup\$
    – 884-15-X-C
    Feb 6, 2018 at 17:37

1 Answer 1

Reset to default
4
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you need to enable Peripheral clock for USART2 explicitly, using this call

RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);

before enabling USART2 with USART_Cmd(USART2, ENABLE);

Also make sure your startup_xx.s file knows the USART2_IRQ_Handler

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13
  • \$\begingroup\$ I enabled the peripheral clock, and the startup_stm32303xc.s does have USART2_IRQ_Handler. The program doesn't work yet. I have used the LEDs on the board for making sure that the program runs. The program initialises completely, and sysTick_Handler works without a problem (that LED keeps blinking - I have set it to toggle after the USART_SendData command). Regardless, there is no output on the TX Pin (PA2) - the oscilloscope shows that this pin at a constant 3.3V. \$\endgroup\$
    – 884-15-X-C
    Feb 6, 2018 at 15:53
  • \$\begingroup\$ Does it come inside the ISR? you also need to clear the pending interrupt bit i.e USART_ClearITPendingBit(USART2, USART_IT_RXNE); inside the ISR. \$\endgroup\$
    – Abel Tom
    Feb 6, 2018 at 16:35
  • \$\begingroup\$ No, I didn't check inside the ISR. Still (correct me if I am wrong), I believe the program should be transmitting even if the ISR is never called (i.e., I don't send anything to the board). \$\endgroup\$
    – 884-15-X-C
    Feb 6, 2018 at 16:56
  • \$\begingroup\$ Its a little unconventional i would say, but you are trying to send data in Systick handler even before USART1 module is initialized. I would start by commenting everything inside systick and put that Send routine in main--> while(1) loop \$\endgroup\$
    – Abel Tom
    Feb 6, 2018 at 16:59
  • 1
    \$\begingroup\$ @NipuniPerera If this is not solving your problem, you should not have marked it as an "answer" as it will deter further answers from being posted. \$\endgroup\$
    – Ron Beyer
    Feb 6, 2018 at 17:21

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