Linker error after adding the RS485 library

maxgerhardt · December 21, 2022, 10:37pm

This is the wrong way. Only add

#include <ArduinoRS485.h>

The intellisense error will go away after doing a Ctrl+Shift+P → Rebuild Intellisense.

And well, as you can read in

github.com

arduino-libraries/ArduinoRS485/blob/master/src/RS485.cpp#L201-L205


      
          {
            _predelay = predelay;
            _postdelay = postdelay;
          }

the RS485 library will, if RS485_SERIAL_PORT is not externally defined, try to use SERIAL_PORT_HARDWARE as its serial port, which as you can see in

github.com

arduino/ArduinoCore-avr/blob/42fa4a1ea1b1b11d1cc0a60298e529d37f9d14bd/variants/mega/pins_arduino.h#L405-L405


      
          #define SERIAL_PORT_HARDWARE        Serial

is Serial.

As you can read in the documentation

https://docs.platformio.org/en/latest/plus/debug-tools/avr-stub.html#debugger-limitations

and in the code

github.com

jdolinay/avr_debug/blob/74f0fa2e3f67982e3d7af5242af066cc91da55dd/avr8-stub/avr8-stub.h#L233-L244


      
          * Supported values for Atmega2560 and Atmega1280:
          * 0 - use USART0 (Arduino Serial cannot be used with the debugger)
          * 1 - use USART1 (Rx=PD2=D19, Tx=PD3=D18)
          * 2 - use USART2 (Rx=PH0=D17, Tx=PH1=D16)
          * 3 - use USART3 (Rx=PJ0=D15, Tx=PJ1=D14)
          * 
          * Note: the number in AVR8_UART_NUMBER is used to generate register names in macros; 
          * don't put it into parentheses.
          */
          #ifndef AVR8_UART_NUMBER
                 #define AVR8_UART_NUMBER       0
          #endif

The AVR-stub code also by default tries to use the Serial object to host the GDB server.

And thus, you have a serial port conflict.

If you wanted to use Serial3 for the RS485 port / transceiver module, add

build_flags = -DRS485_SERIAL_PORT=Serial3

to the platformio.ini (docs).

If it was intentional to use the RS485 library with the default Serial port, you must connect an additional USB-UART adapter to a free serial port and set AVR8_UART_NUMBER accordingly to host the AVR stub server on that serial interface, e.g.

build_flags = -DAVR8_UART_NUMBER=3