Raspberry serial communication with Arduino serial connection: see full blog at http://thomasloughlin.com

echoSerial.c

/*
  Software serial multple serial test
 
 Receives from the hardware serial, sends to software serial.
 Receives from software serial, sends to hardware serial.
 
 The circuit: 
 * RX is digital pin 10 (connect to TX of other device)
 * TX is digital pin 11 (connect to RX of other device)
 
 Note:
 Not all pins on the Mega and Mega 2560 support change interrupts, 
 so only the following can be used for RX: 
 10, 11, 12, 13, 50, 51, 52, 53, 62, 63, 64, 65, 66, 67, 68, 69
 
 Not all pins on the Leonardo support change interrupts, 
 so only the following can be used for RX: 
 8, 9, 10, 11, 14 (MISO), 15 (SCK), 16 (MOSI).
 
 Modified on 5/23/2013 by http://thomasloughlin.com
 created back in the mists of time
 modified 25 May 2012
 by Tom Igoe
 based on Mikal Hart's example
 
 This example code is in the public domain.
 
 */
#include <SoftwareSerial.h>

SoftwareSerial piSerial(10, 11); // RX, TX

void setup()  
{
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  Serial.println("Ready To receive Data");
  piSerial.begin(9600);
 
}

void loop() // run over and over
{
  if (piSerial.available())
    Serial.write(piSerial.read());
  if (Serial.available())
    piSerial.write(Serial.read());
}