1. Interfacing the Raspberry Pi
to the World
Up close and personal with P1 (and P5!)
@OmerK | OSHCAMP 2012 | 15 Sep 2012

2. omer.kilic.name

3. Agenda
● Mechanical Details
● Electrical Details
● Software Details
● Tips for headless operation
● Questions

4. Mechanical
● Standard 100mil (2.54mm) spacing
– P1 → 2x13 way
– P5 → 2x4 way

5. M/F Jumper Cables

6. M/F Jumper Cables

7. IDC Cable
Re-use old floppy cables!

8. http://www.raspberrypi.org/archives/1404

9. “Breakout” boards
Pi Cobbler from Adafruit

10. Slice of Pi from Ciseco
Pi Plate from Adafruit
More at: http://elinux.org/RPi_Expansion_Boards

11. Electrical
● P1
● Power
● 3.3V (max I: ~50mA)
● 5V (max I: Power Supply - 700mA)
● 17 GPIO Pins, multiplexed with:
● UART
● I2C
● SPI
● PWM
● P5
● 4 extra GPIO pins
● Power
● More signals broken out to S2 and S5 (Camera and
flat panel connectors)
● Fiddly!
http://elinux.org/RPi_Low-level_peripherals

12. Revision 2 – Changes
● Fuses protecting the USB outputs have been removed
– Power the board via back-feeding hub
● JTAG on P1
● I2C peripherals swapped
● P5 – New header: 4 more GPIO + Power
● P6 – Reset Jumper
● Mounting holes!!!!!!!!!!!!
http://www.raspberrypi.org/archives/1929

13. Revision 2

14. Power (5V)

15. Electrical
3.3V!

16. 3.3V

17. http://www.flickr.com/photos/56601859@N00/3064468115

18. Use protection
● Level Shifting
– Logic buffers (74HCT242)
– Birectional translators (TXB0108)
– Discrete shifters (FETs + Rs)
● Current limiting R

19. Recommended Distro
Occidentalis by Adafruit
http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/overview

20. Software
● Peripherals are memory mapped
– Access via /dev/mem
● Faster, needs root, hacky, dangerous!
– Use kernel modules/sysfs
● /sys/class/gpio/gpioX/value etc.
● Slower, doesn't need root, easier, (relatively) safer

21. Software – GPIO
● /sys/class/gpio/ (export|direction|value|interrupt|unexport)
● Example:
– echo 17 > /sys/class/gpio/export
– echo “out” > /sys/class/gpio/gpio17/direction
– echo “1” > /sys/class/gpio/gpio17/value
● Interrupt support
– Use poll() on /value

22. Software – I2C
● /dev/i2c-0 and /dev/i2c-1
● Install the i2c-utils package
– i2cdetect, i2cdump, i2cget, i2cset
● Support for kernel hardware modules:
– echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-
0/new_device
● i2c-dev details:
– http://kernel.org/doc/Documentation/i2c/dev-interface

23. Software – SPI
● /dev/spidev0.0 and /dev/spidev0.1
– Chip select pins
● Support for kernel hardware modules:
– Need to rebuild kernel!
● spidev details:
– http://kernel.org/doc/Documentation/spi/spidev

24. Software – PWM
● No kernel module (or libgpio) support, memory
mapped voodoo necessary.
● WiringPi example:
– pinMode(1, PWM_OUTPUT);
– PwmWrite(500);

25. Libraries
● Python
– Quick2wire, Rpi.GPIO
● C
– WiringPi, pihwm
● Bindings also available for Java(!), Ruby, Erlang

26. Tips for headless operation
● Use 240/16 (CPU/GPU) RAM split
– No need for graphical stuff
● Setup avahi/zeroconf
– No need to remember IP address
● ssh raspberrypi.local
● Setup mosh
– Great for intermittent networking

27. Questions?