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STM32F4 USART issue

ethhghg hhhrthrt
Associate
Posted on May 22, 2017 at 01:33

Hello,

I've been trying to send data by uart from stm32f429i board to computer through usb. I learned from the datasheet that two pins - PA9 -tx and PA9-rx are connected to ST-LINK programmer so it seemed possible. I uploaded example code but im only getting weird ASCII chars (but baud rate on both computer and board are the same). Here is the example:

#include <stm32f4xx.h>

#include <misc.h> // I recommend you have a look at these in the ST firmware folder

#include <stm32f4xx_usart.h> // under Libraries/STM32F4xx_StdPeriph_Driver/inc and src

#define MAX_STRLEN 12 // this is the maximum string length of our string in characters

volatile char received_string[MAX_STRLEN+1]; // this will hold the recieved string

void Delay(__IO uint32_t nCount) {

while(nCount--) {

}

}

/* This funcion initializes the USART1 peripheral

*

* Arguments: baudrate --> the baudrate at which the USART is

* supposed to operate

*/

void init_USART1(uint32_t baudrate){

GPIO_InitTypeDef GPIO_InitStruct; // this is for the GPIO pins used as TX and RX

USART_InitTypeDef USART_InitStruct; // this is for the USART1 initilization

NVIC_InitTypeDef NVIC_InitStructure; // this is used to configure the NVIC (nested vector interrupt controller)

/* enable APB2 peripheral clock for USART1

* note that only USART1 and USART6 are connected to APB2

* the other USARTs are connected to APB1

*/

RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

/* enable the peripheral clock for the pins used by

* USART1, PB6 for TX and PB7 for RX

*/

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

/* This sequence sets up the TX and RX pins

* so they work correctly with the USART1 peripheral

*/

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10; // Pins 6 (TX) and 7 (RX) are used

GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF; // the pins are configured as alternate function so the USART peripheral has access to them

GPIO_InitStruct.GPIO_Speed = GPIO_Speed_100MHz; // this defines the IO speed and has nothing to do with the baudrate!

GPIO_InitStruct.GPIO_OType = GPIO_OType_PP; // this defines the output type as push pull mode (as opposed to open drain)

GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_DOWN; // this activates the pullup resistors on the IO pins

GPIO_Init(GPIOA, &GPIO_InitStruct); // now all the values are passed to the GPIO_Init() function which sets the GPIO registers

/* The RX and TX pins are now connected to their AF

* so that the USART1 can take over control of the

* pins

*/

GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1); //

GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1);

/* Now the USART_InitStruct is used to define the

* properties of USART1

*/

USART_InitStruct.USART_BaudRate = baudrate; // the baudrate is set to the value we passed into this init function

USART_InitStruct.USART_WordLength = USART_WordLength_8b;// we want the data frame size to be 8 bits (standard)

USART_InitStruct.USART_StopBits = USART_StopBits_1; // we want 1 stop bit (standard)

USART_InitStruct.USART_Parity = USART_Parity_No; // we don't want a parity bit (standard)

USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None; // we don't want flow control (standard)

USART_InitStruct.USART_Mode = USART_Mode_Tx | USART_Mode_Rx; // we want to enable the transmitter and the receiver

USART_Init(USART1, &USART_InitStruct); // again all the properties are passed to the USART_Init function which takes care of all the bit setting

/* Here the USART1 receive interrupt is enabled

* and the interrupt controller is configured

* to jump to the USART1_IRQHandler() function

* if the USART1 receive interrupt occurs

*/

USART_ITConfig(USART1, USART_IT_RXNE, ENABLE); // enable the USART1 receive interrupt

NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn; // we want to configure the USART1 interrupts

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;// this sets the priority group of the USART1 interrupts

NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; // this sets the subpriority inside the group

NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; // the USART1 interrupts are globally enabled

NVIC_Init(&NVIC_InitStructure); // the properties are passed to the NVIC_Init function which takes care of the low level stuff

// finally this enables the complete USART1 peripheral

USART_Cmd(USART1, ENABLE);

}

/* This function is used to transmit a string of characters via

* the USART specified in USARTx.

*

* It takes two arguments: USARTx --> can be any of the USARTs e.g. USART1, USART2 etc.

* (volatile) char *s is the string you want to send

*

* Note: The string has to be passed to the function as a pointer because

* the compiler doesn't know the 'string' data type. In standard

* C a string is just an array of characters

*

* Note 2: At the moment it takes a volatile char because the received_string variable

* declared as volatile char --> otherwise the compiler will spit out warnings

* */

void USART_puts(USART_TypeDef* USARTx, volatile char *s){

while(*s){

// wait until data register is empty

while( !(USARTx->SR & 0x00000040) );

USART_SendData(USARTx, *s);

*s++;

}

}

int main(void) {

init_USART1(115200); // initialize USART1 @ 9600 baud

USART_puts(USART1, 'abcdefghijklmnoprstuwxyz\r\n'); // just send a message to indicate that it works

while (1){

//USART_puts(USART1, 'Init complete! Hello World!\r\n');

}

}

// this is the interrupt request handler (IRQ) for ALL USART1 interrupts

void USART1_IRQHandler(void){

// check if the USART1 receive interrupt flag was set

if( USART_GetITStatus(USART1, USART_IT_RXNE) ){

static uint8_t cnt = 0; // this counter is used to determine the string length

char t = USART1->DR; // the character from the USART1 data register is saved in t

/* check if the received character is not the LF character (used to determine end of string)

* or the if the maximum string length has been been reached

*/

if( (t != '\n') && (cnt < MAX_STRLEN) ){

received_string[cnt] = t;

cnt++;

}

else{ // otherwise reset the character counter and print the received string

cnt = 0;

USART_puts(USART1, received_string);

}

}

}
2 REPLIES 2
Posted on May 22, 2017 at 11:10

Hi

rgrfggr.grfga

,

JW

Posted on May 22, 2017 at 13:52

Make sure PLL settings and HSE_VALUE reflect an 8 MHz clock source.

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