MRAA

Introduction

libmraa is a low-level library, developed by Intel, for accessing the I/O functions (GPIO, I2C, SPI, PWM, UART) on a variety of boards such as Intel's Galileo and Edison boards, MinnowBoard Max, Raspberry Pi, and more. It is written in C/C++ and provides Python and Javascript bindings. libmraa supports the UP board since (v0.9.5).

upm is a high-level library that makes use of mraa, and provides packages/modules to manage a variety of sensors and actuators. v0.5.1.

Setup

Note: If using Ubuntu 18.04, for UP Xtreme please follow dedicated installation instruction in the dedicated section below

To install and ensure that the most up-to-date version is installed, please run the following commands:

 sudo add-apt-repository ppa:mraa/mraa
 sudo apt-get update
 sudo apt-get install mraa-tools mraa-examples libmraa2 libmraa-dev libupm-dev libupm2 upm-examples
 sudo apt-get install python-mraa python3-mraa libmraa-java

For javascript/nodejs support, it is recommended to install mraa using npm instead:

 $ sudo apt-get update
 $ sudo apt-get install nodejs nodejs-legacy npm
 $ npm install mraa

Setup for UP Xtreme i11 and UP Squared 6000 on Ubuntu 20.04

After Installing Ubuntu 20.04 Desktop for IoT Platforms, please follow these instructions to install an updated version of MRAA libraries with support for UP Xtreme i11 and UP Squared 6000:

 sudo add-apt-repository ppa:up-division/mraa
 sudo apt-get update
 sudo apt-get install mraa-tools mraa-examples libmraa2 libmraa-dev libupm-dev libupm2 upm-examples
 sudo apt-get install python3-mraa libmraa-java

Setup for UP Xtreme on Ubuntu 18.04

The necessary changes for supporting UP Xtreme have been upstreamed to the official MRAA Github Repository:

Unfortunately, the deb pre-packaged version available on the official launchpad repository for Ubuntu 18.04 still does not include the latest changes. If using Ubuntu 20.04 the official launchpad repository includes the necessary changes. We have compiled and pre-packaged the MRAA libraries in our repository and you can download and install following these steps:

 sudo add-apt-repository ppa:aaeonaeu/libmraa
 sudo apt-get update
 sudo apt-get install mraa-tools mraa-examples libmraa-dev libmraa2
 sudo apt-get install python-mraa python3-mraa node-mraa libmraa-java
 sudo reboot

Usage

The following page contains links to examples and API documentation for mraa :

• https://github.com/intel-iot-devkit/mraa

Examples are installed on UP at the following path:

/usr/share/mraa/examples/

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Warning: In MRAA the GPIO pins are numbered according to the physical pin numbers (1-40) instead of using Rpi notation (see the pinout reference)

Warning: For executing the following script root access is required

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Example 1: Blink an LED on a GPIO output pin

The following Python script will blink an LED connected to GPIO 22 (pin 15) at a rate of 1Hz:

#!/usr/bin/python

import sys
import mraa
import time

# Use pin 7 by default
pin_no = 15

# Export the GPIO pin for use
pin = mraa.Gpio(pin_no)

# Small delay to allow udev rules to execute (necessary only on up)
time.sleep(0.1)

# Configure the pin direction
pin.dir(mraa.DIR_OUT)

# Loop
while True:
    # Turn the LED on and wait for 0.5 seconds
    pin.write(1)
    time.sleep(0.5)
    # Turn the LED off and wait for 0.5 seconds
    pin.write(0)
    time.sleep(0.5)

This is javascript version of the example above:

var m = require('mraa'); //require mraa

var myLed = new m.Gpio(7); //LED hooked up to digital pin 7
myLed.dir(m.DIR_OUT);      //set the gpio direction to output
var ledState = true;       //Boolean to hold the state of Led

function periodicActivity()
{
    myLed.write(ledState?1:0);           //if ledState is true then write a '1' (high) otherwise write a '0' (low)
    ledState = !ledState;                //invert the ledState
    setTimeout(periodicActivity,500);    //call the indicated function after 1 second (1000 milliseconds)
}

periodicActivity(); //call the periodicActivity function

Example 2: Turn an LED on/off by detecting a button press on a GPIO

In this example, an LED is connected to GPIO output 23 (pin 16), and a button connected to GPIO input 24 (pin 18). The LED will turn on when the button is pressed.

#!/usr/bin/python

import sys
import mraa
import time

ledPin = 16
buttonPin = 18

# Export the GPIO pins for use
led = mraa.Gpio(ledPin)
button = mraa.Gpio(buttonPin)

# Small delay to allow udev rules to execute
time.sleep(0.1)

# Configure the pin directions
led.dir(mraa.DIR_OUT)
button.dir(mraa.DIR_IN)

# Loop
while True:
    # If button input is HIGH, turn LED off
    value = button.read()
    if value:            # If button input is LOW, turn LED on
        led.write(0) 
    else:
        led.write(1)

Example 3: Fade an LED using hardware PWM

This script will slowly fade on/off an LED connected to PWM0 (pin 32)

NOTE: this needs to be run as root user

#!/usr/bin/python

import sys
import mraa
import time

ledPin = 32

led = mraa.Pwm(ledPin)
led.enable(True)
duty = 0.0

try:
    while 1:
        while duty < 1.0:
            led.write(duty)
            duty += 0.05
            time.sleep(0.1)
        while duty > 0.0:
            led.write(duty)
            duty -= 0.05
            time.sleep(0.1)
except KeyboardInterrupt:
    pass

led.write(0)
led.enable(False)

Example4: Control an I2C device

This script controls the voltage on a MCP4725 DAC from Sparkfun (https://www.sparkfun.com/products/12918) connected to I2C-1 (pins 3, 5)

#!/usr/bin/python

import mraa
import sys

dac = mraa.I2c(0)
dac.address(0x60)

DEVICE_REG = 0x40

# DAC VOUT level is a 12-bit number (0-4095)
# 0 = 0V, 4095 = VCC

level = 2048
if (len(sys.argv) > 1):
    level = int(sys.argv[1])

if (level > 4095):
    level = 4095
if (level < 0):
    level = 0

data = [DEVICE_REG, level >> 4, (level & 0xF) << 4]
dac.write(bytearray(data))