atoi() function returning garbage to terminal STM32, C lang

Question

I have some question about atoi() function. I'm trying to convert string data received from HAL_UART_Receive_IT function to integer and next to sent again to terminal. And what I have at the exit it Looks like garbage
enter image description here

This is part of my code

uint8_t UART_Rx_Data;
----------------------
while (1){
  HAL_UART_Receive_IT(&huart2, (uint8_t*)&UART_Rx_Data, sizeof(UART_Rx_Data));
}
----------------------
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart){
  if (huart == &huart2){
    int i = atoi((char *)&UART_Rx_Data);
    HAL_UART_Transmit_IT(&huart2, (uint8_t *)i, sizeof(i));
  }
}

How to get integer from UART_Rx_Data?

*I really believed that there was a problem with atoi function, because another part of my code looks like

if (huart == &huart2){
  unsigned int Left_El = atoi((char*) &UART_Rx_Data);
    for(unsigned int i = 0; i <= 4095; i++){
      if(i == Left_El){
        unsigned int ADC_Rx_Data = round((i * (100.0 / 4095.0)) + 25);
          __HAL_TIM_SET_COMPARE(&htim21, TIM_CHANNEL_1, ADC_Rx_Data);
      }
    }
}

I need just to receive integer data from UART and add duty cycle to TIM, but it doesn't work. I tried to check why, and when I send throw UART data it turned out that there have garbage. Now I will try remade by loop "for" for the reason like mentioned below that atoi waits for "\0"

Answer 1

This line of your posted code passes the value of the variable i cast to an address to the function HAL_UART_Transmit_IT(), not the address of the value contained in i:

HAL_UART_Transmit_IT(&huart2, (uint8_t *)i, sizeof(i));

Per the documentation for HAL_UART_Transmit_IT() that I found:

...

Parameters:

huart pointer to a UART_HandleTypeDef structure that contains the configuration information for the specified UART module.

pData Pointer to data buffer

Size  Amount of data to be sent

The second argument - pData in the documentation - is a pointer to (or the address of) the data to be sent.

This would match that documentation:

HAL_UART_Transmit_IT(&huart2, (uint8_t *) &i, sizeof(i));

Note the addition of the & "address-of" operator to i.

Answer 2

Your code makes no sense.

You receive one byte and then call the function which requires C string. It is undefined behaviour and you will not receive number from the terminal this way.

Then you send the binary representation of the integer to the text terminal (assuming that you have added & to the variable). It makes no sense at all.

It is hard to understand what you want to archieve.