Chris Adams says 33M boxes in 2001...........................
techweb.com
March 29, 1999, Issue: 1153
Section: Inside: Internet Appliances
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Revising The Script For Set-Top Boxes -- As the market emerges, chip designers are addressing the evolving technology.
John H. Mayer
Although "set-top box" has yet to become a household phrase, the terminology is expected to roll off the tongue a little more readily in the next few years.
Predictions made a few years ago that there would soon be a set-top in every home were premature. But the success of early implementations such as DirectTV, coupled with an emerging cable-modem standard, have spurred the development of the market, undeterred by the limited reach of WebTV Networks, the first interactive set-top box.
OEMs are finally ready to build interactive boxes for viewing high-quality Internet content, using electronic program guides, and layering sophisticated graphics and video windows on standard TV monitors.
With such advances, C-Cube Microsystems Inc. projects that unit shipments of set-top boxes will grow from 6 million in 1997 to 33 million in 2001.
"The performance bar has been raised, particularly in the area of graphical user interface," said Chris Adams, vice president of marketing and systems solutions at C-Cube, Milpitas, Calif. "The original boxes that hit the market were basically passive. They let you do things with the box that you used to do with your analog TV. Now, we're going into a product generation where people want the kind of graphics display that they can get on a PC."
Re-examining the strategy
Placing an added premium on processor performance, these new functionality requirements are forcing OEMs to re-examine when and where they want to integrate functions on-chip.
The concept of a set-top box is undefined today, and no one is quite sure what should be in it, and what it should or shouldn't do, according to Bill Turley, an analyst with MicroDesign Resources Inc., Sebastopol, Calif.
"Every OEM that we've talked to that has a processor inside some sort of single-chip set-top box is now rethinking that strategy, because the ability of set-top boxes to incorporate additional functionality has outgrown their embedded processors," said Glenn Pohly, business development manager at Hitachi (Semiconductor) America Inc., Brisbane, Calif. "As a consequence, they either have to respin the ASIC, which is a very significant cost, or consider just keeping in the ASIC the set-top-box functionality and leaving the processor outside."
The market is a moving target, said John Charles Bouzigues, business development manager at Integrated Device Technology Inc., Santa Clara, Calif. He cited a recent decision by Tele-Communications Inc. (TCI), Englewood, Calif., the largest U.S. cable-system operator, to scale back production and redefine a new generation of set-top boxes.
"The market is definitely there, but you need to be able to adapt very quickly to evolving market requirements," Bouzigues said.
The features users want are changing rapidly, and the key to retaining flexibility is processor performance, he said. "Your processor has to have the ability to handle that variation in software, rather than relying on having the necessary gates in hardware that an ASIC approach implies."
To meet the performance needs of the latest-generation set-top boxes without violating cost constraints, IDT recently introduced the RC32364, a 32-bit controller that drives processing costs less than 10 cents/mips. Fabricated in a 0.30-micron CMOS process technology, the 133-MHz processor achieves 175- Dhrystone mips and 67 million multiply-accumulate operations per second (MACs/s). The chip features a two-way associative cache memory (8-Kbyte instruction, 2-Kbyte data), a 64-bit compatible memory management unit with a 32-page translation look-aside buffer for fast virtual-to-physical address decoding, and a flexible external bus.
For higher-performance applications, IDT extended its 64-bit microprocessor line with the RC64474 and RC64475. Last month, the company added a family of system controllers for its new processor line that supply a range of standard functions, including SDRAM control, memory and I/O control, a PCI interface, and common peripherals.
The breadth of a vendor's product line may, in fact, become a key criterion for OEMs as the market segments into low-end, midrange, and higher-end devices. "It allows you to offer a basic set-top box that can give a consumer his analog or digital video and little else, and then a higher-end set-top box that capitalizes on a more powerful processor and peripherals to support cable modem and voice-over-IP [Internet protocol] technology," Hitachi's Pohly said.
Hitachi is offering its SH-3 microprocessor line for low-end implementations, and its SH-4 products for higher-performance designs. The SH-3 line includes the SH7729, which combines a controller and DSP on one die.
"We probably wouldn't recommend it for a basic set-top box, but in applications where you need both kinds of functionality, such as extensions to set-top boxes for voice-over-IP applications or videoconferencing applications, it's a good fit," Pohly said.
IC vendors generally set a baseline performance level for a low-end digital set-top box at about 50 to 60 mips just to control the peripherals and ASICs. But some processor cores, such as ARM Ltd.'s ARM9, which is capable of delivering up to 220 mips, are enabling designers to put more functions into software and to simplify the hardware design.
"With CPU bandwidth rising, companies are implementing a wide variety of hardware and software partitions," said Joe Frisby, manager for business development at ARM, Cambridge, England. "MPEG-2 decoding, for example, is walking the edge between a hardware and software implementation."
Hitachi's strategy is to offer a customer a processor core with a memory interface-SDRAM, DMA, UART-and timer, and then let the OEM differentiate its set-top-box design with ASICs that perform the video, graphics, I/O, and security functions, according to Pohly.
"We offer middleware that can do Dolby AC-3 and some MPEG transport demux, for example, but typically it's the customer's decision whether to incorporate that into an ASIC or use processor mips and software to accomplish the same functions," he said.
New design challenges
The market is in a high state of flux, as vendors move to more interactive solutions and cope with evolving audio, cable-modem, and voice-over-IP technologies. Whichever way OEMs decide to go, they'll have plenty of options.
For those trying to deliver interactive features such as Web-browsing over television, C-Cube integrates MPEG-2 decoding, multiplanar graphics, two-way networking capabilities, and a CPU into its AViA@tv chip. A number of set-top makers, including Pace Micro Technology, Philips Electronics, and Pioneer Digital Technologies, have selected the IC for new-generation set-tops.
One of the biggest challenges facing OEMs planning to offer HTML content on a TV screen is that they will have to dramatically improve picture quality, according to C-Cube's Adams. Unlike PCs, TVs typically use an interlaced display that draws alternate fields 30 times a second for a total rate of 60 frames/s above the threshold of human perception. When images originally created for PC displays are rendered on an interlaced TV screen, however, the eye detects the lower refresh rate as a flicker.
"If you display an object entirely in one field and not another, such as objects with sharp lines like the horizontal top edge of a window on a PC screen, it falls within the threshold range of the human eye and the object appears to flash," Adams said.
To eliminate that problem, the C-Cube chip includes a Flicker Filter designed to improve the picture quality of HTML content over the TV. "So now you can take things like Web pages or graphics content that's running in software on the set-top and display it without concern for this problem," he said.
One key to an interactive set-top platform capable of running e-mail accounts or online home-banking applications is two-way networking support. C-Cube's AViA@tv integrates this capability by adding a media-access controller (MAC) on-chip.
"Two-way interactivity over HFC [Hybrid/Fiber Coax] networks is critical for the MediaOne deployment," said Jos Swillens, general manager of Philips Digital Receivers.
Eindhoven, Netherlands-based Philips is using the AViA@tv chip in a new line of set-top boxes that will support HFC processing for MediaOne. The C-Cube chip will be combined with DiviCom's interactive set-top-box controller and other digital head-end equipment to enable MediaOne to deliver interactive data services.
While IC suppliers say they can integrate all the functionality of a set-top into a single chip, most see little call for it today except in low-end "passive" set-top applications.
"Unless one of the market segments really takes off, a single-chip solution probably doesn't make sense," said David Tahmassebi, director of marketing for the consumer/digital entertainment business unit at VLSI Technology Inc., San Jose.
The need for flexibility
Design flexibility is, again, dictating the partitioning of functions in ASICs. For digital-TV set-top-box applications, VLSI has segmented functionality into three chips: a front-end network interface chip, a transport demultiplexer IC (VES2750), and an MPEG-2 audio/video decoder and system controller (VES6200).
"We have customers who are using the VES2750/VES6200 combination on the back end to attack the cable, satellite, and terrestrial set-top markets, and they're using different front-end chips for each particular market," Tahmassebi said.
"It gives the OEM a lot more flexibility and avoids the high-pin-count, expensive package you'd have with a single-chip solution," said Sam Feldman, senior marketing manager at VLSI.
The VES2750 and VES6200 are fabricated in a new 0.2-micron mixed-signal process. Built around an ARM7 "Thumb" microprocessor core running at 108 MHz, the chipset supports a variety of functions such as 2D graphics acceleration, video and graphics post-processing, scalable fonts, and AC-3 audio decoding. The chips are sampling, with production scheduled for the third quarter. VLSI officials say volume pricing of the VES2750 and VES6200 chipset will be less than $30.
The company also offers the VES1848 return-channel modem chip for U.S. and European two-way cable set-top applications. Supporting interactive hybrid fiber-coaxial communication between set-tops and the cable head-end, the chip integrates a variety of functions, including differential QPSK out-of-band demodulator, return-path synchronization and media-access control, and MPEG-2 transport PID filtering. OEMs could build a typical set-top box for OpenCable applications with the VES1900 cable-network interface, the VES1848 return-channel modem, and the VES2750 and VES6200.
As the market for digital video cable heats up, spurred by the emerging OpenCable specification, IC vendors with established communications, graphics, and video expertise are leveraging their in-house capabilities to bring ever-wider functionality into new set-top silicon solutions.
For example, Broadcom Corp., San Diego, in December announced a chipset for high-end interactive cable-TV set-tops that merges high-speed cable-modem capability with studio-quality graphics, text, and video.
Four ICs make up the Broadcom solution: the BCM3120 QAMLink set-top-box transceiver; the BCM3300 QAMLink single-chip MCNS/DOCSIS cable modem; the BCM7014 advanced 2D/3D TV graphics system; and the BCM7010 set-top-box decoder. The chipset supplies a dual-tuner architecture that supports two 42-Mbits/s downstream channels, a 2-Mbit/s out-of-band channel, and a 20-Mbit/s upstream channel. Besides the integrated cable modem, the device adds MPEG II transport and video decoding with AC-3 audio decoding, support for both analog and digital video, and a 250-MHz MIPS RISC microprocessor.
For satellite-based applications, LSI Logic Corp., Milpitas, spreads the set-top functionality across three chips: the L64724 satellite receiver, the L64005 MPEG-2 audio and video decoder, and the L64108 transport chip. The Acer Group, Taipei, Taiwan, recently adopted LSI's Integra design for a set-top box geared toward the SKYPerfecTV digital direct broadcast satellite service in Japan.
Software debate
The set-top market isn't only in flux on the silicon side. Most of the earlier-generation designs have used off-the-shelf real-time operating systems such as VRTXmc from Mentor Graphics' Microtec division, VxWorks from Wind River Systems, QNX from QNX Software Systems, OS-9 from Microware Systems, or pSOS from Integrated Systems Inc. IBM, for instance, will incorporate a version of OS-9 in set-tops it will sell in Japan for the digital broadcast satellite and digital cable markets.
The latest-generation interactive set-tops are adding more sophisticated middleware. Sony Corp. and General Instrument Corp., for example, signed a contract in December to collaborate on a next-generation cable-TV set-top box that will run Sony's Aperios real-time OS as well as its Home Networking Module middleware.
At the same time, Microsoft Corp. has been pushing its Windows CE operating system as a viable platform for next-generation set-tops. "OEMs are being careful to hedge their bets," Hitachi's Pohly said. "So, while they may not be planning on this generation being a Windows CE set-top box, they're still asking for CE capability because they don't want to eliminate it as an option."
To date, however, Windows CE has won few converts. Silicon vendors attribute this partly to the significant memory requirements that CE places on set-top design.
"Depending on how much of the WinCE libraries you pull in," Frisby said, "it could grow from 16 Mbytes to 28 Mbytes, whereas set-tops in the past have been shipping with about 1 to 2 Mbytes."
But the main reason Microsoft hasn't seen much success is the operating system's poor real-time performance and, according to some vendors, the company's onerous licensing fees. While successful in the handheld-PC and consumer markets, it has never offered the ultrafast response and low latency found in state-of-the-art real-time microkernels. "Some folks are trying to compensate for CE interrupt latency performance issues by turning up the clock, but that impacts CPU bandwidth consumption," Frisby said.
That may not be necessary in the near future, however. Microsoft officials recently indicated that version 3.0 of the platform will move from a downsized desktop clone to an OS with serious real-time capabilities. Purportedly the new OS will add a prioritization scheme that comprises 32 different priority levels, a real-time clock, support for thread-based device drivers, settable device-driver priorities, OS-level timing diagnostics, DLL mechanisms for real-time threads, semaphores, and real-time isolation for non-real-time threads.
Meanwhile, Java is quickly building momentum among OEMs as the standard programming language for future set-tops. TCI, for example, is licensing Sun Microsystems' JavaOS and will use Sun's PersonalJava language for embedded devices in not only its high-end boxes but its low-end and middle-market offerings as well, according to company officials.
In addition, TCI is supporting Sun's JavaTV application programming interface (API). The set-top boxes will be rolled out next quarter.
In a move that could undermine any effort by Microsoft to position the Windows CE kernel as a leading platform for digital TV, the Advanced Television Systems Committee and the Cablelabs Consortium are jointly working to define a Java TV API that would apply to both cable and terrestrial broadcast TV. While Cablelabs has decided not to specify Java in the basic version of the emerging OpenCable specification for next-generation set-tops, it is being considered for a high-end version of the specification. At the same time, members of the European Digital Video Broadcast project have been working closely with Sun to use Java in its Multimedia Home Platform.
"As a standard for writing applications, Java is winning everywhere," said VLSI's Feldman.
-John H. Mayer is a freelance writer based in Belmont, Mass.
Copyright ® 1999 CMP Media Inc.
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