Run Java application for MCP23017 without root permissions? Yes, it is possible!

[Alex Konshin]

I wondered from the very beginning why Pi4J requires root privileges for i2c when they are not actually required in common use cases.
I found out that it is possible to work around and it is easy to do.

      final MCP23017GpioProvider gpioProvider = new MCP23017GpioProvider( I2CBus.BUS_1, 0x21 );
      GpioFactory.setDefaultProvider( gpioProvider );
     
      // create gpio controller
      gpio = GpioFactory.getInstance();

So you just need to create the provider and call GpioFactory.setDefaultProvider before GpioFactory.getInstance.

But you still need to call the following commands before starting you Java application:
sudo modprobe i2c-dev
sudo chmod o+rw /dev/i2c*
You can put them into /etc/rc.local so they will be executed on Raspberry Pi’s startup.


Explanation:

Basically you just should not call com.pi4j.wiringpi.Gpio.wiringPiSetup*. Method com.pi4j.wiringpi.Gpio.wiringPiSetup() is called from constructor of RaspiGpioProvider. This is the default provider and this constructor is called if it was not set explicitly by GpioFactory.setDefaultProvider.

Alex

[Pi4J]

Thank's for sharing that.  If someone has asked that question, I'm not sure I would have readily identified such an easy workaround. 

Thanks, 

Robert