Serial communication between two arduinos

gistfile1.md

Sender (This is a Feather)

#include <Arduino.h>

void setup() {
  // Begin the Serial at 9600 Baud
  Serial.begin(115200);
  Serial1.begin(115200);
  pinMode(13, OUTPUT);
}

void loop() {
  // Serial.write(mystr,12); //Write the serial data
  if (Serial1.available()) { // Receive
    String readString = Serial1.readStringUntil('\n');
    Serial.println(readString);
  }
  else { // Send
    Serial1.print("Sent from Feather (millis) : ");
    Serial1.println(millis());
  }

  digitalWrite(13, !digitalRead(13));
  delay(1000);
}

Receiver (This a teensy 3.2)

#include <Arduino.h>

void setup() {
  // Begin the Serial at 9600 Baud
  Serial.begin(115200);
  Serial1.begin(115200);
  pinMode(13, OUTPUT);
  // The teensy is too fast to boot, let's slow it a little
  // to let enought time to Feather to boot too.
  delay(5000);
}

void loop() {
  // Serial.write(mystr,12); //Write the serial data
  if (Serial1.available()) { // Receive
    String readString = Serial1.readStringUntil('\n');
    Serial.println(readString);
  }
  else { // Send
    Serial1.print("Sent from Teensy (millis) : ");
    Serial1.println(millis());
  }

  digitalWrite(13, !digitalRead(13));
  delay(1000);
}