Configurare driver I2S

The default ALSA sound devices supported by the Raspberry Pi 3 are PWM audio output jack and HDMI output. To run this demonstration I2S input and output needs to be enabled. The goal is to use a simple I2S interface that does not depend on a particular DAC or CODEC device that requires configuration over I2C or SPI.

To avoid recompilation of the Linux kernel a loadable kernel module is used. This enables the driver for the I2S peripheral inside the BCM2708 device to be loaded dynamically.

A full description of how to do this can be found in the link below [#]_, however a brief summary of the required steps, found to work on a clean copy of Debian Jessie shipped with ``Noobs``, is show below:

http://www.raspberrypi.org/forums/viewtopic.php?f=44&t=91237

First, update the Raspbian Linux distribution to the latest version (version 4.4.13v7 tested). This may take a few hours::

sudo apt-get update
sudo apt-get dist-upgrade

Before proceeding with the next steps, ensure you have re-booted your Raspberry Pi so that it is running the latest version of Raspbian that you have just downloaded. This can be done using the following command::

sudo reboot

Next, we need to enable I2S in device tree. To do this, edit the file ``/boot/config.txt`` to remove the comment on line 47::

dtparam=i2s=on

The sound card driver depends on the I2S peripheral and Direct Memory Access Controller modules which need to be added to file. To do this, add the following lines to ``/etc/modules`` using your favorite text editor prefixed with ``sudo`` to ensure super user privileges::

snd_soc_bcm2708
snd_soc_bcm2708_i2s
bcm2708_dmaengine

Next, download the kernel source (this may also take a long time to download and extract). The source download script requires the installation of two helper applications that are not installed by default. The installation of these is included below::

sudo apt-get install bc
sudo apt-get install libncurses5-dev
git clone http://github.com/notro/rpi-source
cd rpi-source
python rpi-source
cd ..

Now we have the kernel source downloaded, we can modify the driver source and build the modules needed to enable I2S. We require two modules --- one called ``loader`` which instantiates the sound-card module and the other is ``asoc_simple_card`` which is the sound card driver itself.