Media Processor Cuts Time to Market
Programmable DSPs are capable of handling a variety of data formats, including DVD players, the Internet and digital satellite broadcasting.From the beginning of 1997 media processors with performances of 3 to 4 billion operations-per-second (BOPS) (8-bit operation equivalent) have been appearing in the market (Fig 1). Media processors are digital signal processors (DSP) optimized for image and communication processing applications, and can be reconfigured with software. The latest media processors offer ample performance for applications like digital video disk (DVD) players and digital set-top boxes.
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Manufacturers of media processors have shifted their primary target from personal computers (PC) to consumer electronics (Fig 2).
When first announced, media processors were promoted as a one-chip solution integrating all the multimedia functions needed by the PC. The TriMedia chip from Philips Semiconductor NV of the Netherlands, for example, was adopted by Apple Computer Inc of the US for use in the next version of the Macintosh computer. At the same time, Microsoft Corp of the US adopted TriMedia and the Multimedia Signal Processor developed by Samsung Electronics Co, Ltd of Korea, in Talisman, its next-generation three-dimensional (3D) graphics processing architecture. Others, however, including Chromatic Research Inc of the US, predict that "...media processors will be incorporated into 40% of all PCs."
Yoshihiro Nitobe, manager, Section 3 (PC & Multimedia) Semiconductor Segment, Marketing Department, Toshiba Corp of Japan, said, "The PC manufacturers define our Mpact media processor as a graphics accelerator. Once that definition is fixed, we are forced into a number of restrictions, like having to drop power dissipation below one watt, or the inability to use IC chips requiring off-chip RAMDAC which is a digital-analog converter with a built-in color palette."
The force of the media processor has been further weakened by the appearance of 86-family microprocessors with enhanced video processing functions. Widespread use of the Pentium II processor with MMX instruction sets would reduce the need for media processors in the PCs. Low-end PCs do not have the price margin to incorporate both an 86-family microprocessor and a media processor.
New Markets Appearing
Media processors have plenty of leeway, however, since new consumer products do not always have 86-family processors.
"We will use our own media processor, the Media Core Processor, as a second-generation IC in DVD players, and have stopped using a dedicated IC with hard-wired logic," says Susumu Koike, director of Corporate Semiconductor Development Division at Matsushita Electric Industrial Co, Ltd of Japan. More and more manufacturers of consumer electronics are moving in the same direction.
Consumer electronics already use a wide range of data formats and transfer standards for applications such as DVD players, the Internet and digital satellite broadcasting.
Support for a variety of data formats is needed for the Internet. A variety of existing formats, such as Joint Photographic Experts group (JPEG), graphics interchange format (GIF), and tag image file format (TIFF), used for still pictures, are being joined by new formats like FlashPix, which facilitates image scaling.
According to a source at an electronics mass merchandiser in Akihabara, an electronics street in Tokyo, "Internet televisions are hard to sell. The main drawback is content in formats like the portable document format (PDF), which cannot be read easily. We can't really recommend the systems to our customers."
Even television receivers, the prime example of equipment using a fixed image format for decades, are finally on the verge of offering multiple formats.
Advanced television (ATV), the next generation of television in the US, did not develop with a single standard. Instead ATV must support 18 different formats simultaneously.
Programmable ICs Ideal
"It would be ideal if we could provide consumer products with a framework that allowed us to add support for new data formats on the consumer's side," said Toshio Kumagaya, senior manager, Engineering Department II, TV Systems Division, AV Systems Group, Sharp Corp of Japan. Manufacturers want a development stance which will allow them to release products supporting newly-standardized formats as soon as possible, even if they can't be adjusted on the consumer side. For the requirements of consumer electronics in image and communication processing, the best choice seems to be microprocessors, media processors and other programmable chips.
Consumer electronics products have traditionally used microprocessors and DSPs to handle auxiliary things like the processing for television remote controls and audio filters. Media processors and microprocessors are now used for the primary functions of consumer electronics, such as image decoding.
One engineer at a major consumer product manufacturer revealed, "Intel has started coming to us, marketing the Pentium II and other processors for use in consumer products. The trouble is, they are charging about 50 times more than our budget allows."
The inexpensive and programmable media processor, on the other hand, offers processing performance exceeding that of the PC microprocessor.
Accuracy vs Performance
New architectures are being developed for media processors, which specifically handle a narrower range of processing, such as motion video encoding/decoding and communications control. Functions provided in existing microprocessors and DSPs for the support of previous software resources are being cut to improve the price/performance ratio. The fundamental development policy, according to Toyohiko Yoshida, manager, Mediaprocessor Architecture LSI Development Department B, Mitsubishi Electric Corp's System LSI Laboratory of Japan, is recognizing the fact that "video processing and the like just don't need the memory protect functions and double-precision floating point operations that most microprocessors provide."
One characteristic of media processors, cutting operation precision, makes it possible to increase the degree of parallelism in simultaneous operations. Most of the data to be processed for audio and video streams is 8- or 16-bit; pixel data for color video, for example, uses 8 bits each for red, green and blue (RGB). The precision of a 32-bit reduced instruction set computer (RISC) microprocessor, for example, is absurdly overspec here. What is required is a chip that can simultaneously process large volumes of data.
A key advantage of the media processor is that the software development environment is already well-known and developed. This is important when consumer product manufacturers have to develop their own software. The processing used by consumer electronics involves massive data streams, but the actual programming code is relatively small. Most media processors have under 50 lines of code, and even the large ones rarely more than 200. Integrated circuit (IC) manufacturers offering media processors claim that there is little software development load even without a C compiler.
Reducing Part Counts
In addition to providing support for a wide variety of data formats, the media processor is being adopted because it can reduce the number of parts needed in the product. Processing, formerly handled by a number of circuits, can be handled by making use of time multiplexing to simplify circuits.
When the D30V from Mitsubishi Electric is used to implement an MPEG-2 decoder, for example, tasks like video data and audio data separation, inverse quantization and inverse discrete cosine transform (DCT) can be multiplexed sequentially (Fig 3). Frame memory for motion compensation is accessed using a direct memory access (DMA) controller, with the D30V handling predictive frame reconfiguration and differential data adding. In addition to MPEG-2 decoding, the D30V can also be used for modem processing at 56 kbits/s.
Sharp uses the Data Driven Media Processor (DDMP) developed for its multipurpose printer, a combination of printer, scanner, facsimile and copier (Fig 4). A conventional design for a multipurpose printer required 19 gate arrays and 12 first-in, first-out (FIFO) memories. Using the DDMP to handle image processing eliminates three gate arrays and the number of required FIFO memories is slashed to two.
There are cases where dedicated ICs are also needed. Dedicated chips will probably be used in television receivers to support digital broadcasting for the time being. Media processors or microprocessors available in 1997 and 1998 will not be able to handle digital high-definition television (HDTV) processing (1080I or 1080P) on a single chip, although they certainly could do so with multiple chips. Sharp estimates that it would take 16 DDMPs, running at 3.8BOPS, to implement all functions fully (Fig 5).
Improvements in media processor performance will at some point enable digital TV sets to be implemented with a single chip. Philips Semiconductor, for example, plans to release a chip capable of handling the processing for digital TV receivers. This future version of the firm's TriMedia-3 is expected to configure a complete receiver with only the addition of memory and a few analog ICs. The firm has scheduled the fourth quarter of 1999 as a release date.
Sony Corp of Japan is prototyping digital set-top boxes for two approaches: one using a media processor, and one using dedicated ICs. The firm is trying to find the optimum configuration for consumer electronics.
Software Efforts Essential
In order to design the optimum configuration for consumer electronics, manufacturers will first have to decide which functions will be implemented in software, and which in hardware. In order to do that, engineers must have the necessary skills.
Consumer electronics manufacturers have traditionally been short on software engineers. In the development of a standard television receiver, for example, it was common only to assign one or two software engineers to a model. Without additional investment in software development it will be very difficult to support new data formats and standards, even with a media processor capable of quickly and flexibly handling changes in standards.
Sanyo Electric Co, Ltd of Japan assigned about a dozen software engineers to the development of the "Internetter," the firm's Internet-capable television, according to Hideaki Nanko, senior manager, Products Planning Department, Sanyo Electric's CE Media Business Headquarters. Matsushita Electric has transfered engineers from the consumer electronics divisions to the semiconductor group to develop software for the media processor.
In fact, one of the reasons Matsushita Electric switched to a media processor-oriented configuration in its DVD player development was to establish the requisite technology as soon as possible.
From SIMD to VLIW
From an architectural viewpoint, the various media processors (Table 1) are highly individual. Those for video processing use parallel-processing single instruction stream, multiple data stream (SIMD), very long instruction word (VLIW) and data-driven architectures.
Media processor development can either stress the operating frequency or the degree of parallelism (Fig 6). Each manufacturer makes its choice based on its product strategy.
If the operating frequency is the priority, circuit configuration is simplified, and the media processor core is kept as small as possible. Typical examples are Mitsubishi's D30V and the Multi Media Assist from Fujitsu, Ltd of Japan, which offer operating frequencies of 250 and 180MHz, respectively. These chips have media processor core sizes of only 8.0 and 4.3mm2, thanks to circuit simplification.
Boosting the operating frequency makes it possible to achieve top performance. Chips designed to emphasize higher frequency are assumed to integrate a variety of peripheral circuits, implemented through the application specific IC (ASIC) design environment. Manufacturers are preparing ASIC libraries, as Mitsubishi's Yoshida explains, "The D30V is already described in the very high-speed IC hardware description language (VHDL)." Fujitsu's Multi Media Assist is scheduled to support the virtual socket interface (VSI) which is aimed at the standard interface for megacells, according to Shousuke Mori, senior manager, Processor Design Department, PC & AV System LSI Division, Fujitsu.
Chips stressing parallel processing, on the other hand, offer a complete solution as an application specific standard product (ASSP). This includes chips like the Mpact from Chromatic Research, Philips' TriMedia, the Multimedia Signal Processor manufactured by Samsung Electronics, Matsushita Electric's Media Core Processor, and Sharp's Data-Driven Media Processor. Most of these chips also provide special instructions and operators for specific processing tasks, in addition to boosting parallel performance.
by Motoaki Itoh
