AV data transfer – that's infotainment
19 March 2008
The IDB-1394 vehicle-oriented networking standard is now available as an alternative to MOST (Media Oriented Systems Transport).
Leading automotive manufacturers are developing a new generation of invehicle entertainment systems for automotive applications, featuring high quality video and audio functionality for rearseat passengers and driver information displays. Initial models based on MOST (media oriented system transport) are expected later this year. However, rear-seat entertainment systems and cameras will require more bandwidth in the future. Offering bandwidths of up to 400Mbit/sec and the integration of audio, video and realtime data transmission, IDB-1394 promises to be a viable concept.
IEEE 1394b-2002 defines an extension of up to 400Mbit/sec for the physical layer, along with the ability to connect different system nodes of different speed categories without the need to replace the faster nodes or cabling. The network enables the aggregation of multiple communication channels on a single wire harness serving DVD players, PCs and handheld products by dividing audio and image contents into different logical channels which can be transmitted simultaneously.
The IDB-1394 protocol supports various packet types featuring differing timing behaviour. Isochronous (real-time) channels guarantee a defined bandwidth and latency for the payload, while asynchronous channels are typically used to move user commands. Video and associated audio content is routed through isochronous channels along with any audio signals synchronised with the image data at the receiving node.
Traditionally, transport streams (TS) are transferred carrying raw or encoded data. Encoding and decoding functions as part of the IDB-1394 standard are realised using the SmartCODEC function. Contrary to the majority of standards, (including USB), no host processors are required. IDB-1394 enables the implementation of a protocol handler independent of a host processor.
The network can be implemented as a simple linear string, or a ring. The ring structure results in improved system availability because the failure of a partial segment will not result in any data loss in the connected data sources or sinks. Disconnecting only one branch within the network will not lead to system failure. When two DVD-streams coded as MPEG2-TS are fed into the network, they are available for any receiving node, allowing random selection by either of the rear-seat passengers.
The MB88387 IDB controller
Each IDB-1394 node needs a dedicated network device. The MB88387 is a singlechip concept which includes the protocol (data link) layer and the physical layer. There is also a DTCP (digital transmission copy protection) solution which has been developed by a number of companies, including Sony, Intel and Hitachi.
The three functional sections of the MB88387 IDB controller (transmission/reception of audio/video data and isochronous data exchange via asynchronous channels) are depicted in figure 2. The arrow at the bottom of the diagram, identified as MPEG2-TS, outlines the processing of compressed video data TS. Working in a full-duplex mode, the linklayer implementation of the IDB controller provides all of the network’s data streams at both ports.
The MB88387 controller provides an I2S interface for audio, two video interfaces, and one parallel interface for command data issued by the host processor. Asynchronous transmission channels of the IDB-1394 protocol are used for commands including menu control functions. The host processor interface is buffered by two 512Byte FIFOs for reception and transmission. The audio stream, which is handled via a separate isochronous channel, is connected to the I2S interface and buffered by a 2kByte FIFO. In addition, an independent 2kByte FIFO buffer is available for video data streaming. Linear PCM audio and DVD audio can be transmitted via this path.
Separate buffering of all data types enables two streams to be processed simultaneously. For example, digital TV and DVD video signals can be transmitted in parallel while the corresponding audio signals are bundled in separate channels.
At the receiver side, the video stream and the associated audio stream need to be resynchronised following reception. Before passing the data to the DTCP section, the units designated as bridge A/B first reassemble the isochronous packets of corresponding audio and video contents.
In a second step, the TSP-IC interface synchronises these packets according to their time stamps. The TSP-IC unit adds the time stamps to both the MPEG2-TS and audio streams during transmission. Audio and video streams are separated and reassembled automatically. Packet headers are also stripped automatically. All streams are buffered, ensuring a continuous transmission.
The system consists of a main unit (M) located in the dashboard, two-rear seat displays (R), and an amplifier (A). The main unit, which typically includes the navigation section, supplies DVB-T, DVD-Video and DVD-Audio. The rear-seat passengers can randomly select all sources because all streams are transmitted in parallel at all times. The DVB-T signal is converted to a MPEG2 transport stream. It simultaneously provides approximately 30 programmes, resulting in a bandwidth requirement of around 32Mbit/sec. The DVD video signal is also encoded as MPEG2-TS, requiring approximately 36Mbit/sec. The linear PCM Audio signal requires less than 10Mbit/sec. Therefore, only one third of the available bandwidth of an S400 IDB-1394 network is occupied, leaving plenty of room for extensions.
The MB88387SK starter kit available from Fujitsu is a low-cost evaluation platform which can be configured as a receiver or transmitter, providing interfaces for A/V signals of a DVD player or an LCD screen. Fujitsu MPEG2 encoders and decoders (MB83691 and MB86H22 SmartMPEG) are available for processing the MPEG2 transport stream.
The IDB-1394 demonstration network resembles the basic IDB-1394 network consisting of two starter kits. However, in this case, four nodes are connected to the network; two of which are linked to DVD players acting as data sources while the two remaining nodes act as data sinks using the rear-seat displays.
The design requirements of rear-seat entertainment (RSE) systems are quite different from networks in which cameras are used. Camera images must be processed without any noticeable latency, giving the driver the same time to react as if he were looking into the rear-view mirror. Therefore, MPEG2 image compression with latencies of up to 300msec is not acceptable because the resulting delays would be noticeable.
An IDB-1394 controller is capable of transferring DVD video, digital TV and navigation graphics, without assistance from external MPEG decoders or encoders. The raw data supplied as YUV and RGB digital signals are compressed to a third of their original size using a codec algorithm characterised by increased efficiency and creativity. Tailored to the requirements of real-time applications, the algorithm also provides additional options for traditional systems lacking an MPEG2-TS interface for integration into the IDB-1394 bus system. Available since 2006, the SmartCodec with a new IDB-1394-compliant controller is capable of compressing and decompressing YUV signals and high-resolution RGB images that are frequently used for navigation displays. Encoding and decoding times range between two and three milliseconds at a constant compression ratio of 3:1 using component video signals based on the BT601 standard; resulting in natural images and high-quality line drawings.
This codec provides designers with two useful benefits. Firstly, new applications are enabled, including real-time camera systems. Secondly, lower-cost implementations of existing applications (including rear-seat entertainment systems) are possible because no external coding/decoding devices are required.
Several vehicle manufacturers have already started using IDB-1394 as the infotainment network of choice in their vehicle platforms. It is predicted that in just a few years, IDB-1394-based entertainment systems will be available in production vehicles.
WOLFGANG WIEWESIEK is manager of automotive networks, Fujitsu Microelectronics Europe.
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