Audio mp3 Decoder with Ir Target Identification for Artistic Sites.
by Nicola Bergamin (see contacts info)

Overview

Mp3 technology breaks into artistic environment with AAplayer, the Arts Audio Player. Mp3 compression of music files is the recognized standard in the audio processing industry, due to its huge popularity among the Internet community. AAplayer is a portable guide, conceived to be used in artistic sites open to visitors such as museums, or open-space sites like archaeological and historical environments.The audio content (speech and music background) is related to the different works of art present in the site, and it is stored in a compressed manner. The visitor (user) simply has to point-and-click the device towards the art piece, thus causing the proper audio track to be executed. The different art pieces are recognized by infrared technology. They have to be equipped by a specifically designed target device.(see)

System details

AAplayer

AAplayer is an ARM-based design for a full Mpeg1-2 layer III decoder.
For important artistic sites, audio quality of speech comment and background music is deemed to be as important as in the HI-FI circle. Mp3 standard allows high quality audio to be stored in the static memory of the AAplayer.
The device has a 32 bit ARM720-based Cirrus Logic EP7209 CPU, internal 64MB NAND flash and external SmartMedia support for audio file storage and programming.
The mp3 software library decodes 64/128/160kbps mp3 stream files, being based on Cirrus Logic mp3 decoder library.
Creation and compression of audio tracks is up to the Manager of the artistic site. Different language contents may be prepared in advance to fulfill the needs of foreign visitors. To this aim, the Manager can easily reprogram the AAplayer by using the removable SmartMedia card.
Power supply is guaranteed by a GS-Melcotech Li-Ion battery, whith enough capacity to withstand 6 hours continuous duty. The battery charger is specifically designed for the AAplayer.

Target

The Target is a small device (about 3x2x1 cm size), battery or solar-cell operated, which is capable to communicate with the AAplayer by InfraRed technology. Each art piece of interest would be equipped with such a target.
When visitor points the AAplayer to one target, this in turn gives identification informations, thus letting the AAplayer to automatically recognize the correct audio track. Allowed distance between target and AAPlayer is about 3 metres.
Two options are available for target supply: battery supply (small Li-Ion cell), or solar cell.
The solar cell system is designed to provide its own energy even by the simple normal lighting of the museum (neon tubes or fluorescent lamps give enough energy to supply the target). This avoids battery replacement in places where the layout is not expected to change.

AAplayer reference design

The AAplayer is available in a reference design form: the Audio Player board can be connected to an auxiliary RAM expansion board, thus forming the AAplayer reference design.
The AAplayer reference design can be used as a ready to start audio development platform, allowing good emulation and debug environment. With the reference design, one can download software into ram, debug it with a JTAG emulator, program the software in code flash, and program audio data into NAND flash.

Software architecture

Software modules developed for this reference design include: mp3 decoding (based on Cirrus Logic object library), DAI (I2S) interface to CS43L43 DAC, user/key interface, smartmedia and NAND flash handling, code flash programming module. Currently available version of the software has been developed by using ARM toolchain (see Tools paragraph).

All the software project is currently being revised, in order to be ported under eCos operating system, and with the usage of GNU tools instead of ARM Tools. The revision will comprise also a bootstrap flash programmer, and the availability of debug capability without JTAG hardware emulator, via serial line.

Tools

Here follows a summary description of hardware and software tools needed to develop with the AAplayer reference design.

Hardware tools

One good emulation tool revealed to be the EPI-Tools Jeeni(see ref): it is a JTAG emulator exploiting the debug features of the ARM720, which is the base of this design.

Software tools

The toolchain used for the development of the current software release is ARM Software Development Toolkit 2.51.
Arm SDT2.51 comprises a C/C++ Compiler, Debugger, Simulator and an integrated development environment: the Arm Project Manager.
One particular advantage of this set of instruments is that Cirrus Logic supplies a demo example software of mp3 decoder and player ready to work.
One obvious disavantage is that these are proprietary tools, and of course they are not free. Anyway, ARM offers free 60 days trial version.

Alternatively, the GNU Tools is a set of Open Source resources comprising: gcc(C/C++ compiler), gdb(inline debugger), Insight(Debugger for Windows), eCos(Real Time Operating System), cygwin(Linux emulation under Windows).
GNU Tools are completely free and available on the Internet, and are widely supported by the GNU community (see references below).
Particularly, the eCos operating system (made freely available by RedHat, formerly Cygnus), is derived by Linux, paying specific attention to the needs of real time embedded systems.

References

Mp3 technology http://www.mp3-tech.org/,
Epi tools http://www.epitools.com/,
Gnu Open Source tools http://www.gnu.org,
Ecos Open Source operating system : http://sources.redhat.com/ecos/,
Arm CPU core http://www.arm.com/,
Cirrus Logic semiconductor manufacturer http://www.cirrus.com,
GS-Melcotech LI-Ion manufacturer http://www.GS-EU.com .

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