Raspberry Pi

Gottfried Haider edited this page Nov 12, 2016 · 118 revisions

Introduction

The (original) Raspberry Pi contained an ARMv6 CPU, 256 or 512 MB RAM. The Raspberry Pi 2 contains a quad-core ARMv7 CPU, 1 GB of RAM. The Raspberry Pi 3 contains a quad-core ARMv8 (64-bit) CPU, which can also be operated in an ARMv7 compatible mode. It contains the same 1 GB of RAM. The Raspberry Pi Zero features the same ARMv6 CPU as the original Raspberry Pi, and 512 MB RAM. They all contain the same Broadcom VideoCore IV graphics processor.

All models primarily run a modified version of the Debian Linux distribution named Raspbian that was made to run on the ARMv6 CPU (and higher).

On the Pi 2 and 3 it is also possible to run other, unmodified Linux distributions, such as Debian or Fedora, since those settled on the ARMv7 architecture as their "baseline" for modern ARM support. Yet on those distributions you might not have the necessary kernel modules and graphics library to make full use of the Pi's peripherals. This page thus specifically talks about running Processing on Raspbian. (see also: General notes about running Processing on ARM)

The Pi 3 is currently used in an ARMv7 compatible mode by the Raspbian distribution, therefore it is equally compatible with Processing and libraries as its other two siblings. (64-bit ARMv8 support is planned for a later stage.)

Download

You can download a full Raspbian image with Processing pre-installed here. This image is based on Processing 3.2.3 and Raspbian release September 2016, and works on all versions of the Pi.

Important: Since the image contained in the ZIP file is larger than 4 GB it is necessary to use extraction utilities that can handle large files, such as The Unarchiver on OS X. (Try this if extracting yields a file with CPGZ extension.)

See the Writing an image to the SD card section on this page for how to transfer the contents of the extracted IMG file onto a microSD card. This differs depending on the operating system you are using.

Alternatively, if you already have an existing installation of Raspbian you want to keep, you can install Processing by running the following in a terminal:

curl https://processing.org/download/install-arm.sh | sudo sh

Important: Due to an issue with recent Raspbian releases, it is necessary to uninstall the package libgles2-mesa before using Processing, to prevent startup errors related to the P2D and P3D renderers. The Raspbian image linked above already has them pre-removed - but on all other Raspbian installations you might need to run the following commands in a terminal:

sudo aptitude remove libgles2-mesa

(see issue for details)

Graphics

The Pi's graphics core exposes OpenGL ES 2.0, which is supported by Processing P2D and P3D renderer, thanks to specific enablement in the underlying library, JOGL. The graphics driver are built around a closed-source driver (found in /opt/vc), which limits our ability to troubleshoot bugs for the moment.

Due to a limitation of this driver, P3D is currently limited to using 2 lights.

Certain sketches might run out of video memory and throw an exception mentioning GL_OUT_OF_MEMORY. You might be able to work around this by changing the memory split - the amount of memory allocated for the GPU from all system memory. To do so, open the Raspberry Pi Configuration (under Menu, Preferences), navigate to the Performance tab, change the amount of "GPU memory" and then restart your Pi.

If your windowed sketches are displayed slightly offset to the window decoration on HDMI displays, try setting disable_overscan=1 in the file /boot/config.txt and restarting. This is a known issue at the moment.

Starting with the February 2016 version, Raspbian also includes an experimental, open source OpenGL driver for the Pi 2. This driver is still in development, but might be worth trying out when experiencing issues with the default one. To enable or disable the driver, run sudo raspi-config and select the GL Driver option under Advanced Options. Note that the new driver currently lacks many features of the existing one, such as the ability to drive screens attached to the DSI interface, support for camera modules or hardware-enabled video decoding.

Hardware I/O

Processing has a new Hardware I/O library that was extensively tested with the Pi.

GPIO

There is no special configuration necessary to use the digital pins with digitalRead(), digitalWrite() etc.

Keep in mind that the Pi uses 3.3V level, rather then the 5V of the Arduino Uno. The pins are said not to be 5V tolerant, so make sure to keep your voltages to 3.3V.

Each pin is rated up to 16 mA per pin, with 50 mA total, across all pins. (The Arduino UNO is 20 mA @ 5V per pin.) Make sure not to draw more current.

The Hardware I/O library's GPIO class uses GPIO numbers with its methods. Those are not the same as the physical pin numbers of the pin header. (see pinout)

I2C

The Pi has one (publicly exposed) hardware I2C interface. To use it in Processing (with the I2C class in processing.io), open the Raspberry Pi Configuration (under Menu, Preferences), navigate to the Interfaces tab, enable I2C and then restart your Pi.

After restarting, I2C.list() should return one interface: e.g. i2c-1 on the Pi 2. The interface is located on pins 3 (SDA) and 5 (SCL) on the Pi's header. (see pinout) Ground is conveniently located right next to it, on pin 6. Use it together with the 3.3V supply on pin 1, since that is the level that the Pi expects.

LEDs

The Pi has two on-board LEDs, led0 and led1, which can be controlled through the LED class in Processing.

Since the regular user (named pi) is by default not permitted to write to the LED device, you must enable this once by running

sudo sed -i 's|exit 0|chmod -R a+rw /sys/class/leds/*\nexit 0|' /etc/rc.local

After a restart, the devices should be read- and writable by any user. (This can be confirmed by running ls -l /sys/class/leds/led0/brightness. The resulting line should start with -rw-rw-rw-.)

On the Pi, led0 is the green (I/O activity) light, while led1 is the red (power) light. They only can be turned on and off, so brightness() values besides 0.0 and 1.0 have no effect.

SPI

The Pi two hardware SPI interfaces, but which share all but the SS (Slave Select) pins. To use it in Processing (with the SPI class in processing.io), open the Raspberry Pi Configuration (under Menu, Preferences), navigate to the Interfaces tab, enable SPI and then restart your Pi.

After restarting, SPI.list() should return two interfaces spidev0.0 and spidev0.1.

The interfaces' pins are located on the Pi's header on pins 19 (MOSI), 21 (MISO), 23 (SCLK), 24 (SS, aka CE0) and 26 (SS, aka CE1). (see pinout) When using spidev0.0, pin 24 (CE0) is being pulled low during a transaction, while pin26 (CE1) remains unchanged. When using spidev0.1, pin 26 (CE1) is being pulled low, while pin24 (CE0) remains unchanged. (This is to be able to address two devices on the same data & clock lines.)

Servo motors

Using the Hardware I/O library's SoftwareServo class, any pin can be used to control standard RC servo motors.

It is recommended to power the motors from an external power source, as shown in this wiring diagram. See the ServoSweep example for more information.

Upload to Pi tool

The Upload to Pi Processing tool automatically uploads sketches to attached Raspberry Pi devices and executes them there. (also available from the Contribution Manager)

See the Readme file for all features and configuration options. Please file issues here.

Serial

The Pi has one serial port, exposed on pins 8 (TXD) and 10 (RXD). (see pinout) Like all other pins, these operate on 3.3V TTL levels, instead of the RS-232 voltage levels normally expected from a computer's "serial port". By default, the serial port is used to be able to command the Pi remotely, by offering a "shell", through which one can type in commands and receive screen output as on a local terminal.

To use it instead with Processing's Serial library, open the Raspberry Pi Configuration (under Menu, Preferences), navigate to the Interfaces tab, disable Serial and then restart your Pi. The serial port will be called /dev/ttyACM0.

Using USB-connected Arduino boards, etc., is possible without any configuration. They will show up as /dev/ttyUSB0, etc.

Touchscreen

The simpletouch library makes it possible to use any multi-touch-enabled display or trackpad with Processing, as long as the device is supported by the Linux kernel. This library is available through the Contribution Manager under the name "Simple Touch".

This works well with the official Raspberry Pi display, and allows for tracking of up to 10 fingers.

Two example sketches the library comes with explain how to use it. Please file issues here.

Video library

Use the new GL Video library to make use of the Raspberry Pi's accelerated video decoding hardware. (also available from the Contribution Manager)

Examples show the various ways the library can be used. Please file issues here.

Video library: Capture

If you're receiving the error IllegalArgumentException: No such Gstreamer factory: v4l2src with the (regular) Video library, try installing the necessary packages by executing sudo aptitude install gstreamer0.10-plugins-good in a terminal.

Alternatively, the GL Video library also contains some (very limited) functionality for using capture hardware. See this example for details.

If you want to use the Raspberry Pi camera with the GL Video library, add the following line to your /etc/modules file and reboot:

bcm2835_v4l2

After the reboot your camera should show up as /dev/video0.

Other libraries (OpenCV, OpenKinect, PureData, etc)

See General notes about running Processing on ARM.