linux-rs485-stack

Linux ↔ ESP32 RS485 communication stack using ESP-IDF and Linux userspace UART programming.

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Overview

This project demonstrates bidirectional RS485 communication between:

• Linux userspace UART application
• ESP32 firmware using ESP-IDF
• RS485 transceiver modules

The project focuses on low-level serial communication concepts including:

• UART configuration
• RS485 transport
• packet-based communication
• Linux serial programming with termios
• ESP-IDF UART driver usage
• communication debugging and testing

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System Architecture

Linux UART Application
          ↕
USB ↔ RS485 Adapter
          ↕
RS485 Bus
          ↕
ESP32 UART + RS485 Module

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Repository Structure

linux-rs485-stack/
│
├── esp_rs485_driver/
│   ├── main/
│   ├── CMakeLists.txt
│   └── sdkconfig
│
├── linux_uart_app/
│   └── uart_app.c
│
├── README.md
├── .gitignore
└── .gitattributes

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Features

Linux Side

• POSIX UART serial programming
• UART configuration using termios
• Blocking UART RX/TX
• Raw byte stream handling
• Graceful application shutdown using signal handling
• Continuous UART receive loop

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ESP32 Side

• ESP-IDF UART driver
• RS485 packet transmission
• Packet checksum generation
• UART RX/TX debugging
• Continuous packet transmission testing

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UART Configuration

Parameter	Value
Baudrate	115200
Data Bits	8
Stop Bits	1
Parity	None
Flow Control	Disabled

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Example Packet

AA 55 01 56

Byte	Description
AA	Start Byte
55	Command
01	Data
56	Checksum

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Linux Build

Compile:

gcc uart_app.c -o uart_app

Run:

sudo ./uart_app

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ESP32 Build

Build firmware:

idf.py build

Flash firmware:

idf.py flash

Open serial monitor:

idf.py monitor

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Hardware Used

• ESP32 Development Board
• RS485 UART Module
• USB ↔ RS485 Adapter
• Linux Host Machine / VM

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Current Status

• UART communication verified
• RS485 transmission verified
• Linux UART RX/TX verified
• ESP32 UART TX verified
• Packet transmission verified

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Future Improvements

• CRC16 packet validation
• Packet parser state machine
• Timeout handling
• Retry mechanism
• Non-blocking UART
• Multithreaded Linux UART handling
• Modbus RTU support
• Packet framing improvements

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Technologies Used

• C
• ESP-IDF
• FreeRTOS
• POSIX Serial Programming
• UART
• RS485
• Linux

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