| Device profile: empeg car audio player |
Rick Lehrbaum (Oct. 24, 2000)
Product overview
The empeg car audio player, now in its second revision, is basically an in-dash digital music player with a capacity of up to 600 hours of high quality music. You load it with downloaded MP3 files from your PC -- transferred via USB, Ethernet, or a serial port to a pair of internal laptop-style hard drives -- and then you snap it into its docking bay in your car and you're ready to enjoy a seemingly endless choice of your favorite audio entertainment. Additionally, an available FM tuner module option lets you equip the unit to also perform the functions of a car FM radio. 
But don't be misled. Despite the appearance and features of a modern car stereo, inside empeg's car player there lurks a full-function embedded Linux computer! As you'll see, a growing community of empeg enthusiasts is busy creating fun and entertaining applications that run in the empeg system. In short, your car may never be the same once you've added one of these clever devices!
How it operates
As you might imagine, the system's internal Embedded Linux computer comes in extremely handy for searching and navigating through gigabytes of internally stored music files. You control the unit using either the front panel controls or an infrared remote, or with a combination of both. The device also offers voice recognition, which allows hands-free access to common functions including music selection.
The front panel has four ergonomic control buttons plus a rotary control which can be pressed. Each button serves different functions depending on what the player is currently doing, and on whether the button is pressed-and-released or pressed-and-held. All functions can be accessed from convenient drop-down menus. 
On the front, there's a 128 x 31 pixel vacuum-fluorescent display (VFD) which provides a sharp, clear, high-contrast information readout. The VFD is mono (2 bits per pixel), but gray-levels are achieved in software. The display tint is dictated by a user-selected transparent panel chosen at the time of purchase (the choices are blue, red, amber, or green).
While your music is playing, you can place the system's front panel readout in one of several display modes: to provide information about the current track; to show the play line-up; or to display one of many graphical sound visualizations. An interesting (and entertaining) assortment of visualizations can be downloaded into the unit. Some simulated examples may be viewed online, here.
Also located on the front, are an IrDA transceiver and a consumer-IR receiver. These interface with the remote control and also make it possible to communicate with external equipment such as palm-top computers. Currently, there's no "official" empeg software for talking to devices like the Palm PDA; however members of empeg's user community have already come up with software for that purpose.
The connections on the rear of the unit are: a serial port (230 kbps), USB (12Mbit), Ethernet (10BaseT), home audio jacks, and home power jacks, and a docking connector for the in-car mounting bay. 
Technical specifics
Moving inside, the unit's embedded Linux computer is based on a 200 MHz Intel StrongARM system-on-chip processor (info), plus 12MB of RAM memory for program operation and 1MB of flash ROM where the bootstrap software is stored. The CPU has plenty of spare bandwidth to deal with future standards as they arrive. In fact, the player currently uses just 30% of the available CPU bandwidth to decode MP3 files, plot visuals, and deal with file caching. One or two 2.5" laptop drives can be mounted in the shock-mounted cradle within the unit; based on current drive sizes, this allows for up to 36GB of internal storage. 
On the audio side, a Philips in-car SAA7705H DSP manages the digital-to-analog converter (DAC) and controls digital loudness, bass, treble, balance, and fader for the four audio outputs. It also provides a 20-band fully parametric equalizer which can be arranged as stereo 10-band or quad 5-band. The final stage is provided by Burr Brown pre-amps.
The audio decoder software can cope with MPEG 1 layer 3 compression, as well as the higher quality MPEG 2 formats. empeg plans to upgrade this as new standards emerge. One nice feature is that since the audio encoding and decoding are handled in software, there's no risk of being stuck with out-of-date hardware as audio encoding and compression standards evolve.
Speaking of which, the device's internal operating system and application software are fully upgradeable -- generally downloadable free of charge from empeg's website.
Why Linux?
Why did empeg select Linux as the embedded operating system within their device?
The company says they chose Linux for two primary reasons: first, because Linux provides a good development and support environment; second, because Linux is solid and reliable. (It probably didn't hurt that they had full access to source code, and that there are no royalties to pay.)
Unlike some manufacturers of devices based on embedded Linux who strongly discourage hacking, empeg actually promotes having creative users experiment with modifying their product's internal control software. "The boot code is protected," says a comment on the company's website, "so you shouldn't end up with a dead unit."
Accordingly, source code to empeg's Linux kernel modifications, as well as to some other useful routines, is readily available on the company's website. In fact, in an effort to make the unit even more open, a special developer version of the unit's software -- which provides shell access into the box plus a development tool chain -- is also available for download.
To build and support a growing developer community, empeg has established an official empeg developer area on their website. There, you'll find a discussion forum, technical information, software downloads, and even a showcase of hacker accomplishments. For example, one user has programmed the empeg's internal computer to generate a moving map based on input from a GPS receiver; the map is displayed on a Palm PDA. Users wanting to modify their devices will also want to visit the unofficial empeg developer website.
Where can I get one and what does it cost?
Unlike many Embedded Linux devices which are only part way through development, this one is in full production right now. You can order it directly from empeg's online store. The version with 100 hours of music storage capacity (it has a 6 GB internal hard drive) sells for $1199. That comes to about $12 per hour of music it holds. In other words, it costs roughly the same price as the 100 CDs it replaces.
(Click here for further information)
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