Embedded processing demands of in-car multimedia

In the automotive industry, manufacturers are facing a challenge. Consumers are increasingly expecting their new cars to incorporate up-to-date audio and multimedia systems, and interfaces for their portable devices such as MP3 players. With the consumer electronics industry changing at a faster pace than the traditionally slower rate of the automotive industry, the carmakers and tier 1 suppliers must find ways to keep up.

Software flexibility is critical for automotive applications because media formats and communications standards are in a constant state of change. This means that general-purpose processors are often a good choice, as they allow easy, cost-effective changes to automotive multimedia systems.

In-car multimedia also provides a valuable means for manufacturers to differentiate their vehicles from competitors. In this article, we look at Audi's approach to multimedia in the new A5 coupe, and discuss the relevant standards and issues in automotive multimedia.

The Audi system in its new A5 is a good example of a modern in-car multimedia system. Incorporating up to four Blackfin processors, it provides a digital audio broadcast (DAB) radio receiver, an MP3-compliant six-disk CD changer and the Audi music interface that allows users to connect portable media players such as the Apple iPod and use the steering wheel-mounted multifunction controls. Plus, an optional sound surround amplifier by Bang & Olufsen (B&O), which is based on a SHARC processor executing filter algorithms that adapts the audio signals to the vehicle's interior acoustic conditions.

BUS STANDARDS AND OTHER CHALLENGES

From an embedded systems point of view, a major difference between automotive and other applications is the data communications buses. Typically, communication is via CAN or MOST bus. The controller area network (CAN) bus mainly serves as a control interface, with a data transfer rate of about 1 megabit per second (Mbps). Hence, it is not suitable for multimedia data transmission. The media-oriented systems transport (MOST) bus is used to transmit multimedia data in a digital format (raw PCM data) with a data transfer rate of up to 25 Mbps. The necessary MOST and CAN network services are implemented in software, and compliance with real-time requirements is ensured by the real-time operating system (RTOS).

The multimedia system must also support standardized communication protocols, such as USB OTG, SDIO and Bluetooth. It must also support popular devices such as the Apple iPod and Microsoft's Zune player with the required proprietary protocols. USB memories and many different multimedia devices may be connected to the system as USB host. A PC could also be connected to the system as a USB device. As a rule, the USB and SDIO software drivers as well as the respective file systems are integral parts of the operating system.

MULTIMEDIA GATEWAY AND HEAD UNIT

To support automotive multimedia applications, the main tasks of the embedded system (called the multimedia gateway) are the adaptation and conversion of proprietary and standardized communication protocols, such as Bluetooth and USB, as well as decoding of digital audio formats (Figure 1). The multimedia gateway employs custom programmable processors that are open for software updates. It is fast to develop, and enables the automobile manufacturer to react appropriately to the rapid change in the consumer electronics market.

The multimedia gateway has been, until fairly recently, the only solution for vehicles. A new generation of head units will combine the human machine interface (HMI) integrated into the dashboard as well as the multimedia functions of the gateway. The head unit may also include additional functions such as communications and navigation. It requires a substantially greater integration effort than the gateway, and hence lengthens development time, but is much more cost effective.

The software and hardware requirements for the head unit are higher than for the multimedia gateway, since the processor will have to execute the HMI and if necessary a digital radio standard as well as the typical functions for the gateway. The HMI is typically based on a separate processor that is equipped with a direct interface to the display in the vehicle, and may include speech recognition and text-to-speech output. A powerful processor like the Blackfin BF549 can perform the necessary operations while providing a scalable platform.

In the new Audi A5, the multimedia interface (MMI) graphical display of the “Symphony” and “Concert” radio equipment is controlled via the parallel peripheral interface port (PPI) of a Blackfin ADSP-BF539 processor with a clock speed of 533 MHz. The MMI was developed with a state-of-the-art software tool for designing graphical user interfaces. This tool enables users to produce a prototype of the HMI user interface and to simulate additional customized versions.

UNDER THE DASHBOARD

For Audi, the Blackfin processor provided the required performance and connectivity, and the flexibility for field upgradability. Other processor architectures were considered, but Blackfin was chosen as it offered the performance, scalability, and connectivity to handle audio decoding, DAB processing, and MMI control within Audi's automotive infotainment system. It also offered the supporting infrastructure to enable fast, low-risk development.

Optional DAB features are powered by an ADSP-BF532 processor. The Audi Symphony/Concert DAB radio is a software-defined radio (SDR) approach and allows Audi to implement new radio protocols easily with new software. Future upgrades would require only a software flash of new IP to the processor's programmable hardware.

Another Blackfin processor, connected to the MOST bus, drives an MP3-compatible 6-way CD changer. The processor runs the MOST network services in software.

One more Blackfin processor drives the A5's Audi music interface, which integrates portable media players, such as the Apple iPod, for dashboard display and steering wheel control. The interface also replicates the iPod display on the audio screen, including track titles.

At 400 MHz, the processor featured the right price/performance for this application, and the fact that the processor can perform both control and signal processing meant it could handle audio processing and external device management.

Figure 2 shows the internal block diagram of the Blackfin multimedia processor. Connectivity is provided by many serial interfaces (3 SPI, 4 UARTs, 4 SPORTs, 2 TWI) as well as a USB-OTG, an ATAPI and an SDIO interface. In addition, up to three parallel interfaces are available to drive a display screen, a camera and another processor for navigation services. Two CAN and one MXVR interface provide the interface between the processor and the vehicle's internal bus.

A powerful processor is required for automotive multimedia applications. The internal 32-bit-architecture and fast DDR memory interface of the Blackfin BF549 processor is capable of processing video data with a resolution of up to 800 x 480 pixels (WVGA). It also means it can handle demanding scenarios such as processing simultaneous audio files while handling MOST network services and Bluetooth communications.

Developers on all of the design teams for the Audi A5 project used ADI's VisualDSP++ integrated development and debugging environment (IDDE). The environment includes native C/C++ compilers, advanced graphical plotting tools, statistical profiling, and the VisualDSP++ Kernel (VDK), which allows code to be implemented in a structured easy-to-scale manner.

DRM ISSUES

Any purchased tracks may contain files that are digital radio mondiale (DRM) protected. To be able to replay the digital audio, the decoder must support the appropriate DRM format. Decoding Microsoft's DRM (PlaysforSure) requires a DRM certificate that must be saved permanently in the gateway. The storage of the DRM certificate presents a particular challenge, because it is essential that the DRM is properly protected from unauthorized access.

Blackfin processors are protected by a suitable safety concept based on software and hardware authentication. The Lockbox technology was specially developed to deal with digital rights management. The DRM certificate is stored in a special one-time programmable memory (OTP). Access to the OTP is only available via an application that is authenticated during the boot sequence. In addition, the application can also be encoded partially or completely to prevent anyone from spying on or illegally copying the application.

GROWING ROLE OF WIRELESS

In the future, wireless data transmission will play a special role, since this connection method is suitable for the transmission of audio and video data between portable terminal equipment and vehicles. Besides, the well-known profile for hands-free communication (hands-free profile or HFP), the Bluetooth protocol also supports a whole series of new profiles. One of these new profiles is the advanced audio distribution profile (A2DP, which enables the user to reproduce audio files located on a mobile phone via the vehicle's audio-system. A2DP enables compressed audio data, for example MP3 and AAC, to be transmitted using the wireless Bluetooth link.

The AVRCP profile extends the A2DP profile. This profile enables the user to play back music that is located on a mobile phone. This typically includes start, stop, next track, previous track as well as the quick playback of a track. The profile also provides support for metadata. In the future, it will also be possible to display the title on the radio display, to enable the user to select the desired track or play lists via the central user interface.

The dial-up network (DUN) profile is another important profile. This profile provides base station connection options to mobile phones and direct user access to the Internet. The data transmission speed depends on the transmission standard. This means that a large number of new telematics functions are made available.

In addition to pure communication support, the multimedia gateway also handles simultaneous decoding of several digitally formatted audio files that may employ digital rights management (DRM). In the future, two to three separate audio zones will be supported in a vehicle to meet the needs of all the passengers. Table 1 contains an overview of the most important audio codecs.

FUTURE EXPECTATIONS

Following the audio applications the next step will involve video applications that will multiply the hardware requirements. While the data rates required for audio are around a few hundred kbits per second (kbps), the data rates for video will rise to several Mbps. In that case, video data must be distributed in the vehicle from one or several video sources, for example from a DVD or hard disk.

Consequently, in the future the MOST150 standard, which is still being defined, will be able to handle data rates of up to 150 Mbps. The Bluetooth standard will also approach its limits when video data must be transferred since the maximum data rate of 2 Mbps can only be used to replay small video files. For short-range wireless networking, Bluetooth will be replaced by a new wireless USB standard capable of carrying up to 480 Mbps.

The only remaining question is how the vehicle may be connected to the Internet in the future. The trend toward higher data rates will continue.

REFERENCES

Technical specifications for the Blackfin processor family www.analog.com/processors/blackfin/index.html.
Krekels Hans, “Next generation of in-vehicle multimedia,” Automotive Connectivity 2007, Stuttgart.
Sauer, J., “The multimedia-gateway: Bridge between portable devices and the car,” Automotive Connectivity 2007, Stuttgart.
Barr, J., “What Bluetooth can offer,” Automotive Connectivity 2007, Stuttgart.