UART communication problem between Raspberry Pi 4 and STM32F767ZI

Hello everyone,

I'm trying to debug a problem with the UART communication between the raspberry pi 4 and an STM32.

Indeed, I try to send the number 1 from the raspberry pi to the stm32 but I can't get the right result.

Here is the code I implemented on the raspberry pi 4 :

 import serial 
 
 from time import sleep
 
 
 
 ser = serial.Serial(
 
 port = "/dev/ttyS0",
 
 baudrate = 9600,
 
 parity = serial.PARITY_NONE,
 
 stopbits = serial.STOPBITS_ONE,
 
 bytesize = serial.EIGHTBITS,
 
 timeout = 1
 
 ) 
 
data = 1 
 
 while True:
 
 data_str_list = [str(data)]
 
 send_string = ','.join(data_str_list)
 
 ser.write(send_string.encode())
 
 sleep(1)

Here is the STM32 code :

char data_sign[1];
 
 
int main(void)
 
{
 
 
 
 HAL_Init();
 
 SystemClock_Config();
 
 MX_GPIO_Init();
 
 MX_DMA_Init();
 
 MX_USART3_UART_Init();
 
 MX_DAC_Init();
 
 MX_UART4_Init();
 
 MX_TIM6_Init();
 
 
 while (1)
 
 {
 
 /* USER CODE END WHILE */
 
 
 /* USER CODE BEGIN 3 */
 
 
 HAL_UART_Receive(&huart4, data_sign, sizeof(data_sign), 1000);
 
 
 }
 
 /* USER CODE END 3 */
 
}
 
 
static void MX_UART4_Init(void)
 
{
 
 
 huart4.Instance = UART4;
 
 huart4.Init.BaudRate = 9600;
 
 huart4.Init.WordLength = UART_WORDLENGTH_8B;
 
 huart4.Init.StopBits = UART_STOPBITS_1;
 
 huart4.Init.Parity = UART_PARITY_NONE;
 
 huart4.Init.Mode = UART_MODE_TX_RX;
 
 huart4.Init.HwFlowCtl = UART_HWCONTROL_NONE;
 
 huart4.Init.OverSampling = UART_OVERSAMPLING_16;
 
 huart4.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
 
 huart4.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
 
 if (HAL_UART_Init(&huart4) != HAL_OK)
 
 {
 
 Error_Handler();
 
 }
 
}

When I send 1, I get this with the STM32 debug:

Sometimes, the value is 241 but I don't know how to interpret this data. Can you please help me please? I think it's a problem with the data types but I tried to change them but I still can't find the right result.

I also changed the clock frequency of the STM32 but nothing changes. The function HAL_UART returns 0.