Not Receiving UART message from STM32WL5M to Laptop

[Dicko]

Hi there, I have an B-WL5M-SUBG1 evaluation board which uses the STM32WL5M module.

I am having problems with the STM32 receiving a message I am sending it from my laptop via python.

I connect between the stm32 and the laptop via an RS422/485 converter. I've used the converter many times before to read print statements from the stm32.

Here is the stm32 code I am using:

#include "main.h"
#include "stm32wlxx_hal.h"
#include <string.h>
#include <stdio.h>

/* Private variables */
UART_HandleTypeDef huart2;
uint8_t rx_buffer[4];  // Buffer for received data
volatile uint8_t data_received = 0; // Flag for data reception

/* Function prototypes */
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);
void Error_Handler(void);
void check_uart_errors(void);

int main(void)
{
    uint8_t tx_ready[] = "READY\r\n";

    /* Initialize system */
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();

    /* Reset UART2 before use */
    __HAL_RCC_USART2_FORCE_RESET();
    HAL_Delay(10);
    __HAL_RCC_USART2_RELEASE_RESET();

    MX_USART2_UART_Init();

    /* Transmit READY message */
    if (HAL_UART_Transmit(&huart2, tx_ready, sizeof(tx_ready) - 1, 300) != HAL_OK)
    {
        Error_Handler();
    }

    HAL_Delay(10); // Prevent issues

    /* Clear UART RX buffer and start receiving */
    __HAL_UART_FLUSH_DRREGISTER(&huart2);
    memset(rx_buffer, 0, sizeof(rx_buffer));

    if (HAL_UART_Receive_IT(&huart2, rx_buffer, sizeof(rx_buffer)) != HAL_OK)
    {
        Error_Handler();
    }

    while (1)
    {
        if (data_received)
        {
            data_received = 0; // Reset flag

            /* Debug: Print received bytes */
            char debug_msg[50];
            sprintf(debug_msg, "RX CALLBACK: %02X %02X %02X %02X\r\n",
                    rx_buffer[0], rx_buffer[1], rx_buffer[2], rx_buffer[3]);
            HAL_UART_Transmit(&huart2, (uint8_t *)debug_msg, strlen(debug_msg), 300);
            HAL_Delay(10);

            /* Echo back the received 4 bytes */
            if (HAL_UART_Transmit(&huart2, rx_buffer, 4, 300) != HAL_OK)
            {
                Error_Handler();
            }

            /* Restart reception */
            memset(rx_buffer, 0, sizeof(rx_buffer));
            if (HAL_UART_Receive_IT(&huart2, rx_buffer, sizeof(rx_buffer)) != HAL_OK)
            {
                Error_Handler();
            }

            check_uart_errors(); // Check for errors after transmission
        }
    }
}

/**
  * @brief System Clock Configuration
  */
void SystemClock_Config(void)
{
    RCC_OscInitTypeDef RCC_OscInitStruct = {0};
    RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

    __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE2);
    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_MSI;
    RCC_OscInitStruct.MSIState = RCC_MSI_ON;
    RCC_OscInitStruct.MSICalibrationValue = RCC_MSICALIBRATION_DEFAULT;
    RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_6;  // 4 MHz
    RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
    if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
    {
        Error_Handler();
    }
    RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_SYSCLK |
                                  RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2;
    RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_MSI;
    RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
    RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
    RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
    if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
    {
        Error_Handler();
    }
}

/**
  * @brief USART2 Initialization Function
  */
static void MX_USART2_UART_Init(void)
{
    huart2.Instance = USART2;
    huart2.Init.BaudRate = 115200;
    huart2.Init.WordLength = UART_WORDLENGTH_8B;
    huart2.Init.StopBits = UART_STOPBITS_1;
    huart2.Init.Parity = UART_PARITY_NONE;
    huart2.Init.Mode = UART_MODE_TX_RX;
    huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart2.Init.OverSampling = UART_OVERSAMPLING_16;
    huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
    huart2.Init.ClockPrescaler = UART_PRESCALER_DIV1;
    huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
    if (HAL_UART_Init(&huart2) != HAL_OK)
    {
        Error_Handler();
    }
}

/**
  * @brief UART RX Complete Callback
  */
void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
{
    if (huart->Instance == USART2)
    {
        data_received = 1; // Set flag to process received data
    }
}

/**
  * @brief Check UART Errors
  */
void check_uart_errors(void)
{
    uint32_t error = HAL_UART_GetError(&huart2);
    if (error != HAL_UART_ERROR_NONE)
    {
        char error_msg[50];
        sprintf(error_msg, "UART ERROR: 0x%lX\r\n", error);
        HAL_UART_Transmit(&huart2, (uint8_t *)error_msg, strlen(error_msg), 300);
    }
}

/**
  * @brief GPIO Initialization Function
  */
static void MX_GPIO_Init(void)
{
    __HAL_RCC_GPIOA_CLK_ENABLE();

    GPIO_InitTypeDef GPIO_InitStruct = {0};
    /* Configure PA2 and PA3 as Alternate Function (AF7) for USART2 */
    GPIO_InitStruct.Pin = GPIO_PIN_2 | GPIO_PIN_3;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF7_USART2;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
}

/**
  * @brief  Error Handler.
  */
void Error_Handler(void)
{
    __disable_irq();
    while (1)
    {
    }
}

 My python code is this:

#!/usr/bin/env python3
import serial
import time

def main():
    ser = serial.Serial(
        port="COM4",
        baudrate=115200,
        bytesize=8,
        parity='N',
        stopbits=1,
        timeout=2,
        xonxoff=False,
        rtscts=False,
        dsrdtr=False
    )

    print(f"Opened COM4 at {ser.baudrate} baud.")

    # Wait for READY message
    start_time = time.time()
    ready_received = False
    while time.time() - start_time < 5:
        line = ser.readline()
        if line:
            decoded = line.decode(errors="replace")
            print("MCU says:", decoded, end='')
            if "READY" in decoded:
                ready_received = True
                break
    if not ready_received:
        print("No READY message received from MCU.")
        ser.close()
        return

    # Clear UART buffer before sending
    ser.reset_input_buffer()
    time.sleep(0.1)

    # Send 4 bytes
    test_msg = b"DATA"
    print("\nSending:", test_msg)
    ser.write(test_msg)
    ser.flush()

    # Wait for response with timeout
    timeout = time.time() + 5
    while time.time() < timeout:
        line = ser.readline()
        if line.startswith(b"RX CALLBACK: "):
            print("MCU Debug:", line.decode(errors="replace").strip())
            continue
        elif len(line) == 4:
            print("Received:", line)
            break
    else:
        print("Error: No response received from STM32.")

    ser.close()
    print("Done.")

if __name__ == "__main__":
    main()

and my output from python is:

Opened COM4 at 115200 baud.
MCU says: READY

Sending: b'DATA'
Error: No response received from STM32.
Done.

Does anybody have any ideas on what the problem is here and how I could fix it. Any help would be greatly appreciated.

Thank you.

[Andrew Neil]

Have you tested the code using just a terminal?

Have you used the STM32 debugger to see what (if anything) the MCU actually receives from the PC, and if it thinks it sends anything back?

---

@Dicko wrote:

I connect between the stm32 and the laptop via an RS422/485 converter..

---

Show the full schematic of this connection

[STTwo-32]

Hello @Dicko 

If you are connecting the B-WL5M-SUBG1 to a RS485 port, you should configure the USART2 on mode RS485. After doing that, please debug the code to see if the message is received or not on the MCU side.

Best Regards.

STTwo-32

[Dicko]

Thanks for the advice Neil. I will try this first thing tomorrow. Although I’ve never used the STM32 debugger. I’ll try and figure it out and let you know the results. 

[Dicko]

Thanks for the advice STTwo-32. I’ve been trying to find some information about USART3 for this board but it’s not mentioned in any of the schematics. 

[STTwo-32]

In this module, there is only 2 USARTs and an LPUART. there is not any other UART IP.

Best Regards.

STTwo-32

[Dicko]

Ah, but you said to configure USART3?

[STTwo-32]

Is just a typo. I've rectified. Thank you so much.

Best Regards.

STTwo-32

[Dicko]

Ah thank you. I set up USART2 as Asynchronous, I guess RS485 is a different option. I’ll look at this tomorrow too. Thank you.  

[Andrew Neil]

With RS485, you have to deal with enabling/disabling the transmitter.

But you said you're using "an RS422/485 converter" - so maybe that doesn't matter in your case?

That's why you need to give full details of how you have this setup - eg, a schematic.

Is there any particular reason for going RS422/485 ?