PureData patch Running on a BeagleBoard from Rafael Vega on Vimeo.

If you don't want to read the whole thing and just want to play a PD patch on your
BeagleBoard, read part 2 of this article.

0. Motivation.

1. There is a large number of open-source software tools for working with audio. From low level programming tools to full-fledged digital audio workstations. On another side, there are musicians, producers and sound designers who use many hardware tools and there are few open-hardware alternatives for musical applications.

2. Audio designers, musicians and producers don't usually have software development skills and need graphic tools for audio processing. Many of them want to take their algorythms to stage or to the studio "in a box".

This is a small step towards the possible development of an open and portable audio processing platform.

1. High level description of the system.

1. The BeagleBoard is an open-hardware, portable, low cost, low power, compact and expandable computer. It is ideal for deploying applications that need a certain amount of processing but don't need all the paraphernalia that a regular computer has (keyboard, display, etc.) A stomp-box is a good example of such an application.

2. Angstrom Linux is a GNU/Linux distribution designed to run on embedded systems such as the BeagleBoard.

3. ALSA (Advanced Linux Audio Architecture) is a part of the Linux operative system that provides a consistent API to work with different audio hardware devices and implements drivers for such devices.

4. JACK Is a system for handling real-time audio and MIDI. It can connect a number of applications to an audio device and allows them to share audio between them. It runs as a system daemon.

5. Xooky Nabox is an application that I wrote in C++ that uses the libpd library to interpret pd patches. It puts pd patches to work as DSP engines and exposes their functionality as a JACK client. In other words, it's an adapter between PD and JACK, without a GUI.

2. How to use.

What you need:

• A BeagleBoard, I used revision C4.
• A 5 volt AC to DC converter.
• A 1GB or larger SD card and a way to connect it to your computer.
• A computer running Mac OS or Linux (you can use one of the many live CD distributions if youu're running something else and don't want to install Linux on your hard drive).
• A PD patch that you want to play with.

Instructions:

1. Connect the SD card to your computer and immediately run sudo dmesg | tail on a terminal to determine the name that your system is giving the SD card.

2. Download this script and run it. This will erase all the data in the card!

/dev/sdc is the name that my system assigned to the SD card, it will be different on your system. Alternatively, you can create parted or a similar program to create a two partitions on the card labeled "boot" and "Angstrom" and formated as FT32 and ext4 respectively.

3. Download this file, uncompress it and copy the contained files to the boot partition in your SD card. (the order in which you copy the files is important).

4. Download this file, uncompress it and copy the contained files to the Angstrom partition in the SD card.

5. Copy your PD patch to /media/Angstrom/var/xooky/patch.pd

6. Put the SD card on the BeagleBoard, turn the BB on and make some noise :)

3. Building the system from scratch.

3.1. Establish serial communication between the BB and your computer

If your computer does not have a serial port, you need an RS232 to USB cable. Linux systems include a driver for such cables. If you're on Mac OS, you need to get drivers from http://osx-pl2303.sourceforge.net (Snow Leopard) or http://xbsd.nl/2011/07/pl2303-serial-usb-on-osx-lion.html (Lion).

Use an AT/Everex cable to connect the BB to your serial port as described here. If the physical connection is okay, the BB should show up on your system as /dev/tty.PL232<something>. Use the ls /dev/tty* command to find out the identifier that your system assigned to it.

Now, establish serial communication with the board using minicom:

Follow the configuration screens to set these parameters: 115200 8N1, no flow control.

To verify that there's proper communication between the board and your computer, leave minicom open and connected and power cycle the BB. You should see something similar to the following in minicom:

2. Install Angstrom Linux==

First, follow steps 1, and 2 of part 2 of this article.

Then, download the boot files from http://www.angstrom-distribution.org/demo/beagleboard and copy them to the boot partition of the SD card as explained in step 3 of part 2.

Now, download the Angstrom distro and the BB kernel modules from http://www.angstrom-distribution.org/demo/beagleboard/ and copy them to the Angstrom partition of the SD card with the following commands:

Go ahead and put the SC card back in the BB, fire up minicom and power up the BB, you should see Angstrom Linux booting up.

3. Share your computer's internet connection with the BeagleBoard

I chose an IP of198.168.2.202 for the BB and 192.168.2.200 for my computer, you can choose whatever makes sense to you.

First, connect a USB cable between your computer and the BB. Then, using the serial terminal, log in to the linux shell in the BB (root user, empty password) and create the /etc/init.d/local_network file with the following content:

and execute:

Everything is set up on the BB side, now you need to set-up your computer to do packet forwarding or share your internet connection with the BB connected on the USB port. On Mac OS, you can do it using the Network Preference Pane:

On Linux, you can do the same by following the instructions here.

Back on the BB terminal, test the internet connection with wget:

If everything was set up correctly, you can disconnect minicom and the serial cable, leave only the USB connected and ssh from your computer to the BB (It's way more comfortable and simple to do so than using minicom):

4. Installing packages and testing audio i/o

Now that your BB has an active intener connection, you can use Angstrom's package manager to install the stuff needed to start making sounds. First, update the package manager:

Then, configure Angstrom to start in mode 3 (command-line only mode) by default. This will ensure that no GUI programs are running that might use the ALSA driver. When you use ALSA, only one program can access the sound card at the same time.

In /etc/inittab:

Now, install the aplay and arecord programs:

And set the audio levels with alsamixer. (For some reason, the tab key wasn't working for me. You can use f4 and f5 instead):

Left Digital Loopback: Mute
Right Digital Loopback: Mute
DAC2 Analog: 6dB
DAC2 Digital Coarse: 6dB
DAC2 Digital Fine: -10dB
Headset: 6dB

Quit alsamixer and store the levels permanently:

Now, connect a microphone or any sound source to the audio in jack in the BB, connect a speaker or headphones to the audio out jack, record to a wav file and play it back

If the file is successfully created and it sounds when you play it, everything is going just fine.

5. Installing and testing JACK

Install the jack packages:

Start the JACK server:

Start a JACK client (jack_metro is a sample client that implements a metronome)

And connect jack_metro's audio ports to the system's audio outputs. You should hear the metronome clicking every second.

Copy them to the BB:

And copy a PD patch:

Then, in the BB, install the tools for compiling programs:

And compile XookyNabox:

And you should hear your patch!

The last step is to create an init script so that JACK and XookyNabox start automatically when the BB powers up. In /etc/init.d/xooky

And execute: