UART Serial Communication Experiment Based on Raspberry Pi 4B and STM32

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This experiment demonstrates how to establish UART (Universal Asynchronous Receiver/Transmitter) serial communication between a Raspberry Pi 4B and an STM32 microcontroller.

UART Serial Communication Experiment Based on Raspberry Pi 4B and STM32 - Blog - Ampheo

Hardware Requirements

Raspberry Pi 4B
STM32 development board (e.g., STM32F103C8T6, STM32F407, etc.)
USB to TTL serial converter (if needed)
Jumper wires
Breadboard (optional)

Connection Diagram

Raspberry Pi 4B          STM32
---------------------------------
GPIO 14 (TXD)  ------>  USART_RX (e.g., PA3)
GPIO 15 (RXD)  <------  USART_TX (e.g., PA2)
GND           ------>  GND

Note: Ensure both devices share a common ground.

Raspberry Pi Setup

1. Enable UART on Raspberry Pi

Edit the config file:

sudo nano /boot/config.txt

Add or modify these lines:

enable_uart=1
dtoverlay=disable-bt

Reboot the Pi:

sudo reboot

2. Install necessary tools

sudo apt-get install python3-serial

3. Python Code for Raspberry Pi

import serial
import time

# Configure serial port
ser = serial.Serial(
    port='/dev/serial0',  # Default UART port
    baudrate=115200,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS,
    timeout=1
)

try:
    while True:
        # Send data to STM32
        message = "Hello STM32 from Raspberry Pi!\n"
        ser.write(message.encode())
        print(f"Sent: {message.strip()}")
        
        # Receive data from STM32
        if ser.in_waiting > 0:
            received_data = ser.readline().decode('utf-8').strip()
            print(f"Received: {received_data}")
        
        time.sleep(1)

except KeyboardInterrupt:
    print("Communication stopped")
    ser.close()

STM32 Setup (Using HAL Library)

1. CubeMX Configuration

Enable USART peripheral in asynchronous mode
Configure baud rate (must match Raspberry Pi, e.g., 115200)
Enable USART global interrupt (optional for interrupt-based reception)

2. STM32 Code Example

#include "stm32f1xx_hal.h"

UART_HandleTypeDef huart1;

void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART1_UART_Init(void);

int main(void) {
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_USART1_UART_Init();
    
    char rxBuffer[100];
    char txBuffer[100];
    
    while (1) {
        // Receive data from Raspberry Pi
        HAL_UART_Receive(&huart1, (uint8_t*)rxBuffer, sizeof(rxBuffer), HAL_MAX_DELAY);
        
        // Process received data (example: echo back)
        sprintf(txBuffer, "Echo: %s", rxBuffer);
        
        // Send response back to Raspberry Pi
        HAL_UART_Transmit(&huart1, (uint8_t*)txBuffer, strlen(txBuffer), HAL_MAX_DELAY);
        
        // Clear buffers
        memset(rxBuffer, 0, sizeof(rxBuffer));
        memset(txBuffer, 0, sizeof(txBuffer));
        
        HAL_Delay(1000);
    }
}

// USART1 Initialization Function
static void MX_USART1_UART_Init(void) {
    huart1.Instance = USART1;
    huart1.Init.BaudRate = 115200;
    huart1.Init.WordLength = UART_WORDLENGTH_8B;
    huart1.Init.StopBits = UART_STOPBITS_1;
    huart1.Init.Parity = UART_PARITY_NONE;
    huart1.Init.Mode = UART_MODE_TX_RX;
    huart1.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart1.Init.OverSampling = UART_OVERSAMPLING_16;
    if (HAL_UART_Init(&huart1) != HAL_OK) {
        Error_Handler();
    }
}

// Error handler and other necessary functions would go here

Testing the Communication

Upload the code to your STM32 board
Run the Python script on Raspberry Pi:
bash
```
python3 uart_communication.py
```
You should see messages being exchanged between the devices

Troubleshooting

No communication:
- Check wiring connections
- Verify baud rates match on both devices
- Ensure common ground connection
Garbled data:
- Check baud rate settings
- Verify voltage levels (RPi is 3.3V, STM32 may be 3.3V or 5V - use level shifter if needed)

Permission denied errors on Raspberry Pi:

sudo usermod -a -G dialout pi
sudo chmod a+rw /dev/serial0

Advanced Options

Implement interrupt-based reception on STM32 for better performance
Add protocol framing (e.g., start/end markers, checksums) for reliable communication
Use DMA for high-speed data transfer
Implement flow control if needed (RTS/CTS)

This basic UART communication setup can serve as the foundation for more complex embedded systems projects combining Raspberry Pi and STM32 capabilities.