Enable GRBL second serial port for receiving commands on Arduino Mega Board

serial.c

// original see: github.com/gnea/grbl-Mega


#include "grbl.h"

...

void serial_init()
{
  // Set baud rate
  #if BAUD_RATE < 57600
    uint16_t UBRR0_value = ((F_CPU / (8L * BAUD_RATE)) - 1)/2 ;
    UCSR0A &= ~(1 << U2X0); // baud doubler off  - Only needed on Uno XXX

    // by HDO
    UCSR1A &= ~(1 << U2X0); // baud doubler off  - Only needed on Uno XXX

  #else
    uint16_t UBRR0_value = ((F_CPU / (4L * BAUD_RATE)) - 1)/2;
    UCSR0A |= (1 << U2X0);  // baud doubler on for high baud rates, i.e. 115200
    
    // by HDO
    UCSR1A |= (1 << U2X0);  // baud doubler on for high baud rates, i.e. 115200
    

  #endif
  UBRR0H = UBRR0_value >> 8;
  UBRR0L = UBRR0_value;

  // enable rx, tx, and interrupt on complete reception of a byte
  UCSR0B |= (1<<RXEN0 | 1<<TXEN0 | 1<<RXCIE0);

  // defaults to 8-bit, no parity, 1 stop bit

  // HDO: add second serial rx, use same values als UART0
  UBRR1H = UBRR0_value >> 8;
  UBRR1L = UBRR0_value;

  // enable rx, tx, and interrupt on complete reception of a byte
  UCSR1B |= (1<<RXEN1 | 1<<TXEN1 | 1<<RXCIE1);
}

...

// add by HDO
// Data Register Empty Interrupt handler
ISR(USART1_UDRE_vect)
{
  // currently not supported
}


// add by HDO
ISR(USART1_RX_vect)
{
  uint8_t data = UDR1;
  uint8_t next_head;

  // Pick off realtime command characters directly from the serial stream. These characters are
  // not passed into the main buffer, but these set system state flag bits for realtime execution.
  switch (data) {
    case CMD_RESET:         mc_reset(); break; // Call motion control reset routine.
    case CMD_STATUS_REPORT: system_set_exec_state_flag(EXEC_STATUS_REPORT); break; // Set as true
    case CMD_CYCLE_START:   system_set_exec_state_flag(EXEC_CYCLE_START); break; // Set as true
    case CMD_FEED_HOLD:     system_set_exec_state_flag(EXEC_FEED_HOLD); break; // Set as true
    default :
      if (data > 0x7F) { // Real-time control characters are extended ACSII only.
        switch(data) {
          case CMD_SAFETY_DOOR:   system_set_exec_state_flag(EXEC_SAFETY_DOOR); break; // Set as true
          case CMD_JOG_CANCEL:   
            if (sys.state & STATE_JOG) { // Block all other states from invoking motion cancel.
              system_set_exec_state_flag(EXEC_MOTION_CANCEL); 
            }
            break; 
        }
        // Throw away any unfound extended-ASCII character by not passing it to the serial buffer.
      } else { // Write character to buffer
        next_head = serial_rx_buffer_head + 1;
        if (next_head == RX_RING_BUFFER) { next_head = 0; }

        // Write data to buffer unless it is full.
        if (next_head != serial_rx_buffer_tail) {
          serial_rx_buffer[serial_rx_buffer_head] = data;
          serial_rx_buffer_head = next_head;
        }
      }
  }
}

HI
did you design this so that you could use two USART's in grbl at the same time or to use USART1 to replace USART0?

My problem is that i'm trying to use a board from a craft cutter, it has an ATmega2561 on it but they have used to USART1 for the serial to usb connection