Communicate arduino to raspberry pi gpio

I can't seem to find anything on this that is up to date. I need to connect my arduino (barebones atmega328p running @ 8mhz) to my raspberry pi 2 using the gpio pins. I only need to be able to read the serial output on the pi from the arduino. I don't need to program the arduino from the pi or anything. I was wondering if anyone else has had to do something similar.

Any help would be much appreciated!

EDIT: I should note, that I must use the gpio pins and cannot use usb for this project.

read the serial output on the pi from the arduino

  1. Connect TX on the RPi to RX on the Arduino.
  2. Connect the grounds.
  3. Use the serial routines on the Arduino to read the serial port at the correct baud rate.

Note that if the Arduino is running on 5V, you will need a level shifter to send data the other way (Arduino to RPi).