RPi Low-level peripherals

Introduction
In addition to the familiar USB, Ethernet and HDMI ports, the Raspberry Pi offers the ability to connect directly to a variety of electronic devices. These include:
 * Digital outputs: turn lights, motors, or other devices on or off
 * Digital inputs: read an on or off state from a button, switch, or other sensor
 * Communication with chips or modules using low-level protocols: SPI, I²C, or serial UART

Connections are made using GPIO ("General Purpose Input/Output") pins. Unlike USB, etc., these interfaces are not "plug and play" and require care to avoid miswiring. The Raspberry PI GPIOs use 3.3V logic levels, and can be damaged if connected directly to 5V levels (as found in many older digital systems) without level-conversion circuitry.

Note that no analogue input or output is available. However, add-on boards such as the Rpi Gertboard provide this capability.

Links

 * For further specific information about the Raspberry Pi's BCM2835 GPIOs, see: RPi BCM2835 GPIOs.
 * To connect devices to the serial port (UART), see the RPi Serial Connection page.
 * Sample circuits for interfacing the GPIOs with other electronics are shown on the RPi GPIO Interface Circuits page.

= General Purpose Input/Output (GPIO) =

Original Model A and B
.



The Raspberry Pi Model A and B boards have a 26-pin 2.54 mm (100 mil) expansion header, marked as P1, arranged in a 2x13 strip. They provide 8 GPIO pins plus access to I²C, SPI, UART), as well as +3.3 V, +5 V and GND supply lines. Pin one is the pin in the first column and on the bottom row.

Revision 1 PCBs: Raspberry Pis with a revision 1 PCB (September 2012 or earlier) have a different pin assignment on the P1 connector:
 * P1 pin 3 is GPIO 0 / SDA0 (not GPIO 2)
 * P1 pin 5 is GPIO 1 / SCL0 (not GPIO 3)
 * P1 pin 13 is GPIO 21 (not GPIO 27)

Revision 1 PCBs also do not have the P5 header (see below). See this discussion for more details of the changes between Rev 1 and Rev 2 PCBs.

Model A+, B+ and B2
The Raspberry Pi Model A+ and B+ boards, and the Pi 2 Model B, have a 40-pin header marked J8, arranged as 2x20 pins. The first 26 pins are the same as P1 on the A/B boards, with the remaining 14 pins providing additional GPIO and ground pins, and an EEPROM ID feature for auto-configuration with add-on "HAT" boards.

'''GPIO voltage levels are 3.3 V and are not 5 V tolerant. There is no over-voltage protection on the board''' - the intention is that people interested in serious interfacing will use an external board with buffers, level conversion and analog I/O rather than soldering directly onto the main board.

All the GPIO pins can be reconfigured to provide alternate functions, SPI, PWM, I²C and so. At reset only pins GPIO 14 & 15 are assigned to the alternate function UART, these two can be switched back to GPIO to provide a total of 17 GPIO pins. Each of their functions and full details of how to access are detailed in the chipset datasheet.

Each GPIO can interrupt, high/low/rise/fall/change. There is currently no support for GPIO interrupts in the official kernel, however a patch exists, requiring compilation of modified source tree. The 'Raspbian "wheezy"' version that is currently recommended for starters already includes GPIO interrupts.

GPIO input hysteresis (Schmitt trigger) can be on or off, output slew rate can be fast or limited, and source and sink current is configurable from 2 mA up to 16 mA. Note that chipset GPIO pins 0-27 are in the same block and these properties are set per block, not per pin. See GPIO Datasheet Addendum - GPIO Pads Control. Particular attention should be applied to the note regarding SSO (Simultaneous Switching Outputs): to avoid interference, driving currents should be kept as low as possible.

The available alternative functions and their corresponding pins are detailed below. These numbers are in reference to the chipset documentation and may not match the numbers exposed in Linux. Only fully usable functions are detailed, for some alternative functions not all the necessary pins are available for the funtionality to be actually used.

There is also some information on the Tutorial on Easy GPIO Hardware & Software.

Kernel boot messages go to the UART at 115200 bit/s - there are more details on the serial port page.

P1 Header pinout, bottom row
KiCad symbol:

Pin 3 (SDA0) and Pin 5 (SCL0) are preset to be used as an I²C interface. So there are 1.8 kohm pulls up resistors on the board for these pins.

Pin 12 supports PWM.

It is also possible to reconfigure GPIO connector pins P1-7, 15, 16, 18, 22 (chipset GPIOs 4 and 22 to 25) to provide an ARM JTAG interface. However ARM_TMS is not available on the GPIO connector (chipset pin 12 or 27 is needed). Chipset pin 27 is available on S5, the CSI camera interface however.

It is also possible to reconfigure GPIO connector pins P1-12 and 13 (chipset GPIO 18 and 21) to provide an I2S (a hardware modification may be required ) or PCM interface. However, PCM_FS and PCM_DIN (chipset pins 19 and 20) are needed for I2S or PCM.

A second I²C interface (GPIO02_ALT0 is SDA1 and GPIO03_ALT0 is SCL1) and two further GPIOs (GPIO05_ALT0 is GPCLK1, and GPIO27) are available on S5, the CSI camera interface.

Referring to pins on the Expansion header
The header is referred to as "The GPIO Connector (P1)". To avoid nomenclature confusion between Broadcom signal names on the SoC and pin names on the expansion header, the following naming is highly recommended:
 * The expansion header is referred to as "Expansion Header" or "GPIO Connector (P1)"
 * Pins on the GPIO connector (P1) are referred to as P1-01, etc.
 * Names GPIO0, GPIO1, GPIOx-ALTy, etc. refer to the signal names on the SoC as enumerated in the Broadcom datasheet, where "x" matches BCM2835 number (without leading zero) and "y" is the alternate number column 0 to 5 on page 102-103 of the Broadcom document. For example, depending on what you are describing, use either "GPIO7" to refer to a row of the table, and "GPIO7-ALT0" would refer to a specific cell of the table.
 * When refering to signal names, the Broadcom name should be modified slightly to minimize confusion. The Broadcom SPI bus pin names are fine, such as "SPI0_*" and "SPI1_*", but they did not do the same on the I²C and UART pins. Instead of using "SDA0" and "SCL0", "I2C0_SDA" and "I2C0_SCL" should be used; and "UART0_TXD" and "UART0_RXD" instead of "TX" or "TXD" and "RX" or "RXD".

Power pins
The maximum permitted current draw from the 3.3 V pins is 50 mA.

Maximum permitted current draw from the 5 V pin is the USB input current (usually 1 A) minus any current draw from the rest of the board. Be very careful with the 5 V pins P1-02 and P1-04, because if you short 5 V to any other P1 pin you may permanently damage your RasPi. Before probing P1, it is a good idea to strip short pieces of insulation off a wire and push them over the 5 V pins are not accidentally shorted with a probe.
 * Model A: 1000 mA - 500 mA -> max current draw: 500 mA
 * Model B: 1000 mA - 700 mA -> max current draw: 300 mA

GPIO hardware hacking
The complete list of chipset GPIO pins which are available on the GPIO connector is: "0, 1, 4, 7, 8, 9, 10, 11, 14, 15, 17, 18, 21, 22, 23, 24, 25"

(on the Revision2.0 RaspberryPis, this list changes to: 2, 3, 4, 7, 8, 9, 10, 11, 14, 15, 17, 18, 22, 23, 24, 25, 27, with 28, 29, 30, 31 additionally available on the P5 header)

As noted above, P1-03 and P1-05 (SDA0 and SCL0 / SDA1 and SCL1) have 1.8 kohm pull-up resistors to 3.3 V.

If 17 GPIOs are not sufficient for a project, there are a few other signals potentially available, with varying levels of software and hardware (soldering iron) hackery skills:

GPIO02, 03, 05 and 27 are available on S5 (the CSI interface) when a camera peripheral is not connected to that socket, and are configured by default to provide the functions SDA1, SCL1, CAM_CLK and CAM_GPIO respectively. SDA1 and SCL1 have 1K6 pull-up resistors to 3.3 V.

GPIO06 is LAN_RUN and is available on pad 12 of the footprint for IC3 on the Model A. On Model B, it is in use for the Ethernet function.

There are a few other chipset GPIO pins accessible on the PCB but are in use:
 * GPIO16 drives status LED D5 (usually SD card access indicator)
 * GPIO28-31 are used by the board ID and are connected to resistors R3 to R10 (only on Rev1.0 boards).
 * GPIO40 and 45 are used by analogue audio and support PWM. They connect to the analogue audio circuitry via R21 and R27 respectively.
 * GPIO46 is HDMI hotplug detect (goes to pin 6 of IC1).
 * GPIO47 to 53 are used by the SD card interface. In particular, GPIO47 is SD card detect (this would seem to be a good candidate for re-use).  GPIO47 is connected to the SD card interface card detect switch; GPIO48 to 53 are connected to the SD card interface via resistors R45 to R50.

P2 header
The P2 header is the VideoCore JTAG and used only during the production of the board. It cannot be used as the ARM JTAG. This connector is unpopulated in Rev 2.0 boards.



Useful P2 pins:
 * Pin 1 - 3.3V (same as P1-01, 50 mA max current draw across both of them)
 * Pin 7 - GND
 * Pin 8 - GND

P3 header
The P3 header, unpopulated, is the LAN9512 JTAG.



Useful P3 pins:
 * Pin 7 - GND

P5 header
The P5 header was added with the release of the Revision 2.0 PCB design.



P5 Header pinout, top row
As seen from the back of the board:

P5 Header pinout, bottom row
As seen from the back of the board:



Note that the connector is intended to be mounted on the bottom of the PCB, so that for those who put the connector on the top side, the pin numbers are mirrored. Pin 1 and pin 2 are swapped, pin 3 and 4, etc.

An alternative way to attach this header is on top, at a slant away from the P1 header.

The new header can provide a second I²C channel (SDA + SCL) and handshake lines for the existing UART (TxD and RxD), or it can be used for an I2S (audio codec chip) interface using the PCM signals CLK, FS (Frame Sync), Din and Dout.

Note that the connector is placed JUST off-grid with respect to the P1 connector.

P6 header
The P6 header was added with the release of the Revision 2.0 PCB design.



P6 Pinout
A reset button can be attached to the P6 header. Momentarily shorting the two pins of P6 together will cause a soft reset of the CPU (which can also 'wake' the Pi from halt/shutdown state).

Internal Pull-Ups & Pull-Downs
The GPIO ports include the ability to enable and disable internal pull-up or pull-down resistors (see below for code examples/support of this):
 * Pull-up is 50 kOhm - 65 kOhm
 * Pull-down is 50 kOhm - 60 kOhm

Driver support
The Foundation will not include a GPIO driver in the initial release, standard Linux GPIO drivers should work with minimal modification.

The community implemented SPI and I²C drivers, which will be integrated with the new Linux pinctrl concept in a later version of the kernel. (On Oct. 14 2012, it was already included in the latest raspbian image.) A first compiled version as Linux modules is available to install on the 19/04/2012 Debian image, including 1-wire support. The I²C and SPI driver uses the hardware modules of the microcontroller and interrupts for low CPU usage, the 1-wire support uses bitbanging on the GPIO ports, which results in higher CPU usage.

GordonH wrote a (mostly) Arduino compatible/style WiringPi library in C for controlling the GPIO pins.

A useful tutorial on setting up I²C driver support can be found at Robot Electronics - look for the downloadable document rpi_i2c_setup.doc

WebIOPi
WebIOPi allows to control each GPIO with a simple web interface that can be used with any browser. Available in PHP and Python, they both require root access, but the Python version serves HTTP itself. Each GPIO pin can be set up as input or output and its LOW/HIGH stae can be changed. WebIOPi is fully customizable, so it can be used for home remote control. It also works over Internet. UART/SPI/I²C support will be added later. See code examples below.

GPIO Code examples
In case one is interested in the relative performance at toggling gpios for some of the code below, here are benchmarks for original Raspberry Pi, and a comparison of original Pi vs. Raspberry Pi 2:


 * http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/
 * http://codeandlife.com/2015/03/25/raspberry-pi-2-vs-1-gpio-benchmark/

C
Examples in different C-Languages.

Gert & Dom
Gert van Loo & Dom, have provided some tested code which accesses the GPIO pins through direct GPIO register manipulation in C-code. (Thanks to Dom for doing the difficult work of finding and testing the mapping.)

Note: For Raspberry Pi 2, change BCM2708_PERI_BASE to 0x3F000000 for the code to work.

Example GPIO code:

GPIO Pull Up/Pull Down Register Example

// enable pull-up on GPIO24&25 GPIO_PULL = 2; short_wait; // clock on GPIO 24 & 25 (bit 24 & 25 set) GPIO_PULLCLK0 = 0x03000000; short_wait; GPIO_PULL = 0; GPIO_PULLCLK0 = 0;

wiringPi
Get and install wiringPi: https://projects.drogon.net/raspberry-pi/wiringpi/download-and-install/

Save this, and compile with: gcc -o blink blink.c -lwiringPi and run with: sudo ./blink

sysfs
The following example requires no special libraries, it uses the available sysfs interface.

bcm2835
This must be done as root. To change to the root user: sudo -i You must also get and install the bcm2835 library, which supports GPIO and SPI interfaces. Details and downloads from http://www.open.com.au/mikem/bcm2835

pigpio
pigpio provides all the standard GPIO features.

In addition it provides hardware timed PWM suitable for servos, LEDs, and motors and samples/timestamps GPIOs 0-31 up to 1 million times per second (default 200 thousand).

C documentation: http://abyz.co.uk/rpi/pigpio/cif.html

Download and install pigpio: http://abyz.co.uk/rpi/pigpio/download.html

Compile gcc -o pulse pulse.c -lpigpio -lrt -lpthread

Run sudo ./pulse

C#
RaspberryGPIOManager is a very basic C# library to control the GPIO pins via the GPIOPinDriver object. See: https://github.com/AlexSartori/RaspberryGPIOManager

RaspberryPiDotNet library is available at https://github.com/cypherkey/RaspberryPi.Net/. This more advanced library includes a GPIOFile and GPIOMem class. The GPIOMem requires compiling Mike McCauley's bcm2835 library above in to a shared object.

Ruby
This example uses the WiringPi Ruby Gem: http://pi.gadgetoid.co.uk/post/015-wiringpi-now-with-serial which you can install on your Pi with "gem install wiringpi"

Alternatively the Pi Piper Gem (https://github.com/jwhitehorn/pi_piper) allows for event driven programming:

Perl
This must be done as root. To change to the root user: sudo su - Supports GPIO and SPI interfaces. You must also get and install the bcm2835 library. Details and downloads from http://www.open.com.au/mikem/bcm2835 You must then get and install the Device::BCM2835 perl library from CPAN http://search.cpan.org/~mikem/Device-BCM2835-1.0/lib/Device/BCM2835.pm

RPi.GPIO
The RPi.GPIO module is installed by default in Raspbian. Any RPi.GPIO script must be run as root.

More documentation is available at http://sourceforge.net/p/raspberry-gpio-python/wiki/Home/

pigpio
pigpio Python scripts may be run on Windows, Macs, and Linux machines. Only the pigpio daemon needs to be running on the Pi.

pigpio provides all the standard gpio features.

In addition it provides hardware timed PWM suitable for servos, LEDs, and motors and samples/timestamps gpios 0-31 up to 1 million times per second (default 200 thousand).

Python documentation: http://abyz.co.uk/rpi/pigpio/python.html

Download and install pigpio: http://abyz.co.uk/rpi/pigpio/download.html

pigpio scripts require that the pigpio daemon be running.

sudo pigpiod

They do not need to be run as root. ./pulse.py

RPIO
Also available is RPIO at https://pypi.python.org/pypi/RPIO

RPIO extends RPi.GPIO with TCP socket interrupts, command line tools and more.

WiringPi2-Python
There's a Python-wrapped version of Gordon Henderson's WiringPi. See here. import wiringpi2

wiringpi2.wiringPiSetupGpio # For GPIO pin numbering
 * 1) wiringpi2.wiringPiSetup # For sequential pin numbering, one of these MUST be called before using IO functions
 * OR
 * 1) wiringpi2.wiringPiSetupSys # For /sys/class/gpio with GPIO pin numbering
 * OR

wiringpi2.pinMode(6,1) # Set pin 6 to 1 ( OUTPUT ) wiringpi2.digitalWrite(6,1) # Write 1 ( HIGH ) to pin 6 wiringpi2.digitalRead(6) # Read pin 6

Scratch using the ScratchGPIO
Scratch can be used to control the GPIO pins using a background Python handler available from http://cymplecy.wordpress.com/2013/04/22/scratch-gpio-version-2-introduction-for-beginners/

Pridopia Scratch Rs-Pi-GPIO driver
Scratch control GPIO (use GPIO number not P1 pin number can support GPIO 28,29,30,31) support I²C 23017 8/16/32/64/128 GPIO, I²C TMP102 Temp sensor, I²C RTC DS1307, I²C ADC ADS1015, I²C PWM, I²C EEPROM 24c32, I²C BMP085 Barometric Pressure/Temperature/Altitude Sensor, GPIO input/output, DC motor, Relay, I²C 16x16 LED matrix, I²C 24x16 Matrix, 84x48 pixels LCD, 16x2 character LCD, 20x4 character LCD, 1-Wire 18B20 Temp Sensor, Ultra Sonic distance sensor, available from

http://www.pridopia.co.uk/rs-pi-set-scratch.html

RpiScratchIO
Generic interface for GPIO or other I/O operations. The package allows user modules to be easily added and loaded, to interface with any I/O device. The code is written in Python and uses the scratchpy Python package to interface with Scratch.



RpiScratchIO - Installation
To install the package on the latest Raspbian installation type, sudo apt-get install -y python-setuptools python-dev sudo easy_install pip sudo pip install RpiScratchIO

RpiScratchIO - Documentation and examples
More information can be found at https://pypi.python.org/pypi/RpiScratchIO/ The package is also documented in Issues 20 and 22 of The MagPi. RpiScratchIO is the basis of a new BrickPi Scratch handler, which is documented in Issue 23 of The MagPi.



Java using the Pi4J Library
This uses the Java library available at http://www.pi4j.com/. (Any Java application that controls GPIO must be run as root.)

Please note that the Pi4J library uses the WiringPi GPIO pin numbering scheme. Please see the usage documentation for more details: http://pi4j.com/usage.html

More complete and detailed examples are included on the Pi4J website at http://www.pi4j.com/.

The Pi4J library includes support for:
 * GPIO Control
 * GPIO Listeners
 * Serial Communication
 * I2C Communication
 * SPI Communication

Java
This uses the Java library available at https://github.com/jkransen/framboos. It does not depend on (or use) the wiringPi driver, but uses the same numbering scheme. Instead it uses the default driver under /sys/class/gpio that ships with the distro, so it works out of the box. Any Java application that controls GPIO must be run as root.

Java Webapp GPIO web control via HTTP
This uses the Java Webapp available at https://bitbucket.org/sbub/raspberry-pi-gpio-web-control/overview. You can control your GPIO over the Internet. Any Java application that controls GPIO must be run as root.

host:~ sb$ curl 'http://raspberrypi:8080/handle?g0=1&g1=0' {"g1":0,"g0":1}

sysfs, part of the raspbian operating system
The export and unexport of pins must be done as root. To change to the root user see below: To change back, the word exit must be entered. sudo -i Export creates a new folder for the exported pin, and creates files for each of its control functions (i.e. active_low, direction, edge, power, subsystem, uevent, and value). Upon creation, the control files can be read by all users (not just root), but can only be written to by user root, the file's owner. Nevertheless, once created, it is possible to allow users other than root, to also write inputs to the control files, by changing the ownership or permissions of these files. Changes to the file's ownership or permissions must initially be done as root, as their owner and group is set to root upon creation. Typically you might change the owner to be the (non root) user controlling the GPIO, or you might add write permission, and change the group ownership to one of which the user controlling the GPIO is a member. By such means, using only packages provided in the recommended rasbian distribution, it is possible for Python CGI scripts, which are typically run as user nobody, to be used for control of the GPIO over the internet from a browser at a remote location.

wiringPi - gpio utility
You need the wiringPi library from https://projects.drogon.net/raspberry-pi/wiringpi/download-and-install/. Once installed, there is a new command gpio which can be used as a non-root user to control the GPIO pins.

The man page man gpio has full details, but briefly:

gpio -g mode 17 out gpio -g mode 18 pwm

gpio -g write 17 1 gpio -g pwm 18 512

The -g flag tells the gpio program to use the BCM GPIO pin numbering scheme (otherwise it will use the wiringPi numbering scheme by default).

The gpio command can also control the internal pull-up and pull-down resistors:

gpio -g mode 17 up

This sets the pull-up resistor - however any change of mode, even setting a pin that's already set as an input to an input will remove the pull-up/pull-down resistors, so they may need to be reset.

Additionally, it can export/un-export the GPIO devices for use by other non-root programms - e.g. Python scripts. (Although you may need to drop the calls to GPIO.Setup in the Python scripts, and do the setup separately in a little shell script, or call the gpio program from inside Python).

gpio export 17 out gpio export 18 in These exports GPIO-17 and sets it to output, and exports GPIO-18 and sets it to input.

And when done:

gpio unexport 17 The export/unexport commands always use the BCM GPIO pin numbers regardless of the presence of the -g flag or not.

If you want to use the internal pull-up/down's with the /sys/class/gpio mechanisms, then you can set them after exporting them. So:

gpio -g export 4 in gpio -g mode 4 up

You can then use GPIO-4 as an input in your Python, Shell, Java, etc. programs without the use of an external resistor to pull the pin high. (If that's what you were after - for example, a simple push button switch taking the pin to ground.)

A fully working example of a shell script using the GPIO pins can be found at http://project-downloads.drogon.net/files/gpioExamples/tuxx.sh.

pigpio - pigs utility
pigpio provides a command line utility pigs.

pigs provides all the standard gpio features.

In addition it provides hardware timed PWM suitable for servos, LEDs, and motors.

Use man pigs or view the pigs documentation at http://abyz.co.uk/rpi/pigpio/pigs.html

Download and install pigpio: http://abyz.co.uk/rpi/pigpio/download.html

Additional error information may be reported to /dev/pigerr. The following command will display any errors. cat /dev/pigerr & Examples pigs modes 4 w # set gpio4 as output (write) pigs modes 17 w # set gpio17 as output (write) pigs modes 23 r # set gpio23 as input (read) pigs modes 24 0 # set gpio24 as ALT0

pigs servo 4 1500 # start 1500 us servo pulses on gpio4

pigs pwm 17 192 # start 75% dutycycle PWM on gpio17 (192/255 = 75%)

pigs r 23 # read gpio23

pigs w 24 1 # write 1 to gpio 24


 * 1) servo may be abbreviated to s
 * 2) pwm may be abbreviated to p
 * 3) modes may be abbreviated to m

pigs s 4 0 # stop servo pulses

pigs p 17 0 # stop pwm

pigs requires that the pigpio daemon be running.

sudo pigpiod

For an example pigs script see x_pigs in the pigpio archive.

pigpio - /dev/pigpio interface
pigpio provides command line access via the /dev/pigpio pipe.

/dev/pigpio provides all the standard gpio features.

In addition it provides hardware timed PWM suitable for servos, LEDs, and motors.

The command set is identical to that used by pigs. Use man pigs or view the pigs documentation at http://abyz.co.uk/rpi/pigpio/pigs.html

Download and install pigpio: http://abyz.co.uk/rpi/pigpio/download.html

The result of /dev/pigpio commands are written to /dev/pigout. The following command will display the results. cat /dev/pigout & Errors are reported to /dev/pigerr. The following command will display any errors. cat /dev/pigerr & Examples echo modes 4 w >/dev/pigpio # set gpio4 as output (write) echo modes 17 w >/dev/pigpio # set gpio17 as output (write) echo modes 23 r >/dev/pigpio # set gpio23 as input (read) echo modes 24 0 >/dev/pigpio # set gpio24 as ALT0

echo servo 4 1500 >/dev/pigpio # start 1500 us servo pulses on gpio4

echo pwm 17 192 >/dev/pigpio # start 75% dutycycle PWM on gpio17 (192/255 = 75%)

echo r 23 >/dev/pigpio # read gpio23

echo w 24 1 >/dev/pigpio # write 1 to gpio 24


 * 1) servo may be abbreviated to s
 * 2) pwm may be abbreviated to p
 * 3) modes may be abbreviated to m

echo s 4 0 >/dev/pigpio # stop servo pulses

echo p 17 0 >/dev/pigpio # stop pwm

The /dev/pigpio pipe interface requires that the pigpio daemon be running.

sudo pigpiod

For an example /dev/pigpio pipe script see x_pipe in the pigpio archive.

Lazarus / Free Pascal


The GPIO pins are accessible from Lazarus without any third-party software. This is performed by means of the BaseUnix unit that is part of every distribution of Lazarus and Free Pascal or by invoking Unix shell commands with fpsystem. The following example uses GPIO pin 17 as output port. It is assumed that you created a form named GPIO17ToggleBox with a TToggleBox and a TMemo named LogMemo (optional, for logging purposes). The program has to be executed with root privileges.

Unit for controlling the GPIO port: unit Unit1;

{Demo application for GPIO on Raspberry Pi} {Inspired by the Python input/output demo application by Gareth Halfacree} {written for the Raspberry Pi User Guide, ISBN 978-1-118-46446-5}

{$mode objfpc}{$H+}

interface

uses Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, Unix, BaseUnix;

type

{ TForm1 }

TForm1 = class(TForm) LogMemo: TMemo; GPIO17ToggleBox: TToggleBox; procedure FormActivate(Sender: TObject); procedure FormClose(Sender: TObject; var CloseAction: TCloseAction); procedure GPIO17ToggleBoxChange(Sender: TObject); private { private declarations } public { public declarations } end;

const PIN_17: PChar = '17'; PIN_ON: PChar = '1'; PIN_OFF: PChar = '0'; OUT_DIRECTION: PChar = 'out';

var Form1: TForm1; gReturnCode: longint; {stores the result of the IO operation}

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.FormActivate(Sender: TObject); var fileDesc: integer; begin { Prepare SoC pin 17 (pin 11 on GPIO port) for access: } try fileDesc := fpopen('/sys/class/gpio/export', O_WrOnly); gReturnCode := fpwrite(fileDesc, PIN_17[0], 2); LogMemo.Lines.Add(IntToStr(gReturnCode)); finally gReturnCode := fpclose(fileDesc); LogMemo.Lines.Add(IntToStr(gReturnCode)); end; { Set SoC pin 17 as output: } try fileDesc := fpopen('/sys/class/gpio/gpio17/direction', O_WrOnly); gReturnCode := fpwrite(fileDesc, OUT_DIRECTION[0], 3); LogMemo.Lines.Add(IntToStr(gReturnCode)); finally gReturnCode := fpclose(fileDesc); LogMemo.Lines.Add(IntToStr(gReturnCode)); end; end;

procedure TForm1.FormClose(Sender: TObject; var CloseAction: TCloseAction); var fileDesc: integer; begin { Free SoC pin 17: } try fileDesc := fpopen('/sys/class/gpio/unexport', O_WrOnly); gReturnCode := fpwrite(fileDesc, PIN_17[0], 2); LogMemo.Lines.Add(IntToStr(gReturnCode)); finally gReturnCode := fpclose(fileDesc); LogMemo.Lines.Add(IntToStr(gReturnCode)); end; end;

procedure TForm1.GPIO17ToggleBoxChange(Sender: TObject); var fileDesc: integer; begin if GPIO17ToggleBox.Checked then begin { Swith SoC pin 17 on: } try fileDesc := fpopen('/sys/class/gpio/gpio17/value', O_WrOnly); gReturnCode := fpwrite(fileDesc, PIN_ON[0], 1); LogMemo.Lines.Add(IntToStr(gReturnCode)); finally gReturnCode := fpclose(fileDesc); LogMemo.Lines.Add(IntToStr(gReturnCode)); end; end else begin { Switch SoC pin 17 off: } try fileDesc := fpopen('/sys/class/gpio/gpio17/value', O_WrOnly); gReturnCode := fpwrite(fileDesc, PIN_OFF[0], 1); LogMemo.Lines.Add(IntToStr(gReturnCode)); finally gReturnCode := fpclose(fileDesc); LogMemo.Lines.Add(IntToStr(gReturnCode)); end; end; end;

end.

Main program: program io_test;

{$mode objfpc}{$H+}

uses {$IFDEF UNIX}{$IFDEF UseCThreads} cthreads, {$ENDIF}{$ENDIF} Interfaces, // this includes the LCL widgetset Forms, Unit1 { you can add units after this };

{$R *.res}

begin Application.Initialize; Application.CreateForm(TForm1, Form1); Application.Run; end.

Alternative way to access the GPIO port with Lazarus / Free Pascal is by using Lazarus wrapper unit for Gordon Henderson's wiringPi C library or encapsulated shell calls.

The Lazarus wiki describes a demo program that can read the status of a GPIO pin.

BASIC - Return to BASIC
'Return to Basic' (RTB) can be found here.

It is a new BASIC featuring modern looping constructs, switch statements, named procedures and functions as well as graphics (Cartesian and turtle), file handling and more. It also supports the Pi's on-board GPIO without needing to be run as root. (You do not need any special setup routines either)

Sample blink program: // blink.rtb: //   Blink program in Return to Basic //   Gordon Henderson, projects@drogon.net // PinMode (0, 1) // Output CYCLE DigitalWrite (0, 1) // Pin 0 ON WAIT (0.5) // 0.5 seconds DigitalWrite (0, 0) WAIT (0.5) REPEAT END

Bywater BASIC Interpreter
The Bywater BASIC Interpreter (bwBASIC) implements a large superset of the ANSI Standard for Minimal BASIC (X3.60-1978) and a significant subset of the ANSI Standard for Full BASIC (X3.113-1987) in C. It also offers shell programming facilities as an extension of BASIC. bwBASIC seeks to be as portable as possible and is downloadable.

BASIC programming of the I/O
Setting up a GPIO pin to be used for inputs or for outputs.

The control words cannot be loaded directly into the 32 bit ARM registers with 32 bit addresses, as bwBASIC has no POKE and PEEK commands and other versions of BASIC only handle 8 bit registers with 16 bit addresses with these commands. So the GPIO pins need to be exported so that they exist in a file structure which can be accessed from basic with the OPEN command (ref 2).

This must be done in Linux root. BASIC must be run in the root too. sudo -1 sudo bwbasic

Now to export GPIO pin 4 for example, using a Shell command. echo "4" > /sys/class/gpio/export

Whilst bwbasic can accommodate shell commands, and we can store a set of these commands (eg. to export a number of GPIO pins at the outset) as numbered statements in a file that can be loaded with the basic command LOAD "filename" and RUN (ref 2), the shell commands have to run as a separate file, as they cannot be run from within, as part of a basic program.

Now the file containing the pin direction setting from BASIC can be accessed.

GPIO pin 4 can be set to input or output by OPENing its pin direction file for output and writing "in" or "out" with a PRINT# command.

This closes the open direction file, whereupon the system performs the action of setting the direction to "out". The system only carries out the action as the file is closed.

Now the output of the gpio 4 pin can be controlled from BASIC.

GPIO 4 pin can be set to 1 or to 0 by OPENing its pin value file for output and writing "1" or "0" with a PRINT# command. Similarly the output of GPIO pin 4 can be turned off.

Example of an (unstructured) BASIC program
To read the state of a switch and control the power to two LEDs connected to GPIO pins 8,7 and 4 respectively.

Program to set 2 pins as outputs and 1 pin as input and to read the input turning on two different combinations of the two outputs (ie output 0,1 or 1,0) depending on the state of the input (1 or 0).

NEW clears the export.bas program from memory

When all is done, the GPIO pins should be unexported, to leave the R-Pi as we found it. A simple circuit to provide the switched input and the two LED outputs.

For the two original documents this example has been copied from, see:
 * 1) [[Media:GPIO_Driving_Example_(BASIC)_.doc |GPIO_Driving_Example_(BASIC)_.doc]]
 * 2) [[Media:Raspberry_Pi_I-O_viii.doc | Raspberry_Pi_I-O_viii.doc]]

SPI
There is one SPI bus brought out to the header: RPi_SPI

I²C
There are two I²C-buses on the Raspberry Pi: One on P1, and one on P5.

Note that there's a bug concerning I²C-clock-stretching, so don't use I²C-devices which use clock-stretching directly with the Raspberry Pi, or use a workaround. Details about this bug can be found at:


 * http://www.raspberrypi.org/phpBB3/viewtopic.php?f=44&t=13771
 * http://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html

MIPI CSI-2
On the production board, the Raspberry Pi Foundation design brings out the MIPI CSI-2 (Camera Serial Interface ) to a 15-way flat flex connector S5, between the Ethernet and HDMI connectors. A compatible camera with 5 Megapixels and 1080p video resolution was released in May 2013.

DSI
On the production board, the Raspberry Pi Foundation design brings out the DSI (Display Serial Interface ) to a 15-way flat flex connector labelled S2, next to Raspberry Pi logo. It has two data lanes and a clock lane, to drive a possible future LCD screen device. Some smart phone screens use DSI.

CEC
HDMI-CEC (Consumer Electronics Control for HDMI) is supported by hardware but some driver work will be needed and currently isn't exposed into Linux userland. Eben notes that he has seen CEC demos on the Broadcom SoC they are using.

libCEC with Raspberry Pi support has been included in OpenELEC and will be included in Raspbmc RC4.

For more information about HDMI-CEC and what you could do with it on the Raspberry Pi please see the CEC (Consumer Electronics Control) over HDMI article.