Getting Started with MATLAB Support Package for Raspberry Pi Hardware

Introduction

The MATLAB Support Package for Raspberry Pi Hardware enables you to communicate with Raspberry Pi hardware remotely from a computer running MATLAB. The support package includes a MATLAB command line interface for accessing Raspberry Pi hardware's I/O peripherals and communication interfaces. Using this command line interface, you can collect data from sensors connected to Raspberry Pi hardware and actuate devices attached to Raspberry Pi hardware.

In this example you learn how to create a raspi object to connect to Raspberry Pi hardware from within MATLAB. You examine the properties and methods of this object to learn about the status of basic peripherals such as digital I/O pins (also known as GPIO), SPI, I2C, and Serial. Using this object, you execute shell commands on your Raspberry Pi hardware and manipulate files on the Raspberry Pi hardware.

Prerequisites

Required hardware

To run this example you need the following hardware:

Create a raspi object

Create a raspi object.

rpi = raspi();

The rpi is a handle to a raspi object. While creating the rpi object, the MATLAB connects to a server running on the Raspberry Pi hardware through TCP/IP.

Note: If you encounter errors after running the above command, try using additional arguments (as listed in raspi) or refer to Troubleshoot Connecting Issues to Raspberry Pi Hardware.

The properties of the raspi object show information about your Raspberry Pi hardware and the status of some of the hardware peripherals available. Either the numeric IP address or the hostname of your Raspberry Pi hardware and the port used for TCP/IP communication are displayed in the DeviceAddress and Port properties. The raspi object detects the model and version number of your board and displays it in the BoardName property. The GPIO pin-outs and available peripherals change with the model and version of your Raspberry Pi hardware.

The AvailableLEDs property of the raspi object lists user controllable LEDs. You can turn a user LED on or off using the writeLED method.

AvailableDigitalPins, AvailableI2CBuses, and AvailableSPIChannels properties of the raspi object indicate the pins that you can use for digital I/O, I2C buses, and SPI channels that can be used to communicate with sensors and actuators supporting the I2C and SPI communication protocols. It is not an issue if nothing is listed for AvailableSPIChannels. The Raspbian Linux image shipped with MATLAB does not enable the SPI peripheral to provide you with more general purpose digital I/O pins. You can enable and disable I2C and SPI peripherals to suit your needs by loading and unloading Linux® kernel modules responsible for these peripherals.

Turn an LED on and off

There is a user LED on Raspberry Pi hardware that you can turn on and off. Execute the following command at the MATLAB prompt to turn the LED off and then turn it on again.

led = rpi.AvailableLEDs{1};
writeLED(rpi, led, 0);
writeLED(rpi, led, 1);

While executing the preceding commands, observe the 'ACT' (or 'OK') LED on the Raspberry Pi hardware and visually confirm the LED operation. If you are unsure where the user LED is located, execute the following command.

showLEDs(rpi);

You can make the LED blink in a loop with a period of 1 second.

for i = 1:10
    writeLED(rpi, led, 0);
    pause(0.5);
    writeLED(rpi, led, 1);
    pause(0.5);
end

Execute system commands

The raspi object has a number of methods that allow you to execute system commands on Raspberry Pi hardware from within MATLAB. You can accomplish quite a lot by executing system commands on your Raspberry Pi hardware. The system function is limited in MATLAB® Online™.

Try taking a directory listing.

system(rpi, 'ls -al /home/pi')

This statement executes a Linux directory listing command and returns the resulting text output at the MATLAB command prompt. You can store the result in a MATLAB variable to perform further processing. Establish who is the owner of the .profile file under /home/pi.

output = system(rpi,'ls -al /home/pi');
ret = regexp(output, '\s+[\w-]+\s+\d\s+(\w+)\s+.+\.profile\s+', 'tokens');
ret{1}

You can also achieve the same result using a single shell command.

system(rpi, 'stat --format="%U" /home/pi/.profile')

Perform the LED exercise this time using system commands. The user LED is, by default, configured to change its state based on the SD card activity. However, you can reconfigure the LED to change its state based on the requirement of your application. To manually control the LED, set the system command to none:

system(rpi, 'echo "none" | sudo tee /sys/class/leds/led0/trigger');

The system commands with 0 and 1 are equivalent to the writeLED method with arguments 0 and 1 for the LED state.

system(rpi, 'echo 0 | sudo tee /sys/class/leds/led0/brightness');
system(rpi, 'echo 1 | sudo tee /sys/class/leds/led0/brightness');

You can set the LED back to its original state of tracking the SD card activity by executing this command:

system(rpi, 'echo "mmc0" | sudo tee /sys/class/leds/led0/trigger');

You cannot execute interactive system commands using the system() method. To execute interactive commands on the Raspberry Pi hardware, you must open a terminal session.

openShell(rpi)

This command opens a PuTTY terminal. Log in with your user name and password. The default user name is 'pi' and the default password is 'raspberry'. After logging in, you can execute interactive shell commands like 'top'.

The openShell function is not supported in MATLAB Online. Access the command shell remotely via SSH with PuTTY, as described in Remote Access.

Manipulate files

The raspi object provides the basic file manipulation capabilities. To transfer a file on Raspberry Pi hardware to your host computer you use the getFile() method.

getFile(rpi,'/usr/share/pixmaps/debian-logo.png');

You can then read the PNG file in MATLAB:

img = imread('debian-logo.png');
image(img);

The getFile() method takes an optional second argument that allows you to define the file destination. To transfer a file on your host computer to Raspberry Pi hardware, you use putFile() method. This method is not supported in MATLAB Online.

putFile(rpi, 'debian-logo.png', '/home/pi/debian-logo.png.copy');

Make sure that file is copied.

system(rpi, 'ls -l /home/pi/debian-logo.png.copy')

You can delete files on your Raspberry Pi hardware using the deleteFile() command.

deleteFile(rpi, '/home/pi/debian-logo.png.copy');

Make sure that file is deleted.

system(rpi, 'ls -l /home/pi/debian-logo.png.copy')

The preceding command should result in an error indicating that the file cannot be found.

Summary

This example introduced the workflow for using the MATLAB Support Package for Raspberry Pi Hardware. Using the Raspberry Pi support package, you turned the user LED on and off, executed system commands and manipulated files on Raspberry Pi hardware.

See Also

Video series: Raspberry Pi Support for MATLAB