ESP32 ModbusTCP to RTU gateway library

Based on mbusd project

Building

1. Tested on ESP32 IDF v4.1

2. Clone this repository git clone https://github.com/ololoshka2871/esp32-modbusTCP2RTU-gateway-lib.git OR as git submodule git submodule add https://github.com/ololoshka2871/esp32-modbusTCP2RTU-gateway-lib.git to your components folder

3. Add dependency to library to your main module: in main/CMakeLists.txt add line

   idf_component_register(
                   ...
   +++             DEPENDS esp32-modbusTCP2RTU-gateway-lib
   )
   

4. Add code to start gateway (example)

   #include "mbGateway.h"
   
   ...
   
   // After network up...
   mb_gateway_config gateway_config =
       MB_GATEWAY_CONFIG_DEFAULT(1,     // UART1
                                 57600, // speed
                                 4,     // TX pin
                                 2,     // RX pin
                                 16     // RE/DE pin
       );
   // also you can modify defaults in gateway_config
   
   mb_gateway_configure(&gateway_config); // prepare gateway to satrt
   mb_gateway_start(); // new thread will be created

5. Build, flash and run your application

Porting problems

Esp32 VFS drivers has several limitations. So it needs some fixes to get linux library mbusd to work:

1. UARTs represents in ESP32 VFS via /dev/uart/<UART_number>
2. mbusd uses ioctl() to direct control RTS pin. It's unsupported by esp32-idf VFS, so this function disabled at all, but insted of this I use UART_MODE_RS485_HALF_DUPLEX mode see documentation
3. It needs to initalise UART driver BEFORE access it via VFS, see mb_gateway_configure()
4. lwip socket [does not support buffer resize](see http://lwip.100.n7.nabble.com/Setting-TCP-socket-s-send-amp-receive-buffer-size-td10263.html), so, skip buffers modification
5. esp32 VFS select() function for files, what represents UART devices work incorrectly: if UART file descriptor added to select() wait for transmitter ready set, select() allways ends with timeout. To avoid it I create hook my_select(), what skips waiting for UART file descriptor ready to write waiting (assumes it allways ready).
6. Override mbusd's logging to accept ESP32-idf logging style see esp_log.c

Hardware

      VCC ---------------+
                         |
                 +-------x-------+
      RXD <------| R             |
                 |              B|-----------<> B
      TXD ------>| D    ADM483/  |
ESP32            |      ADM3072  |     RS485 bus side
      RTS --+--->| DE            |
            |    |              A|-----------<> A
            +----| /RE           |
                 +-------x-------+
                         |
                        GND

You mast select ESP32 UART pins RXD, TXD and RTS in struct mb_gateway_config