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Low-power processors for Windows CE

A discussion of current proccessor technology (October 98)

Which is more important, size or sex appeal? That’s the question facing many hardware and software designers today. The PC industry gets all the attention, press coverage, and glory—the sex appeal—but the embedded market is far bigger. Contrary to popular belief, embedded CPU chips outsell PC processors by a huge margin. In fact, Pentium and its clones account for less than 1% of the world market for microprocessors. Even high-end 32-bit embedded processors outsold PCs by a 2:1 margin in 1997.

That leaves engineers and product managers with a lot of choices. Which embedded processor to use? How can you pick from among them all? Like a lot of buying decisions, it depends on personal preference, vendor reputation, and knowing what you want. Let’s take a quick look at some of the leading microprocessors for Windows CE applications, particularly those chips that are tailored for low-power, handheld, or portable systems.

There are currently five different processor architectures, or families, that run Windows CE: MIPS, ARM, SuperH, PowerPC, and x86. Matsushita (which is better known by its Panasonic brand name) is working with Microsoft to port Windows CE to its new AM33 processors, too. Each chip family has a different history, different way of doing business, and different pros and cons when it comes time to pick a microprocessor.

Hitachi’s SuperH stealth marketing
Hitachi’s SuperH (also called simply SH) family of microprocessors was almost unknown in North America until Hitachi, Casio, and Compaq started selling HPCs in 1997. Before that time, Hitachi’s best-known design win was with Sega, which uses no fewer than three SuperH processors (plus a Motorola 68000) in every Saturn video game console. Sega’s new Dreamcast system, due late in 1999, uses a brand new SH7750 microprocessor with special 3D acceleration features. Due to its success in video games and handheld devices, SuperH is now one of the best-selling RISC families in the world.

MIPS comes from multiple sources
The MIPS architecture was born out of the supercomputer and workstation environment of the 1980s. MIPS Computer Systems produced one of the few true RISC computers for very high-end users until the company was bought by Silicon Graphics. SGI then started using MIPS processors in its own workstations and developing new MIPS microprocessors in its own design center. Recently, SGI spun off its processor-design subsidiary, and MIPS Technologies is now an independent company.
Unlike Hitachi (and most other microprocessor companies) MIPS Technologies does not actually make any microprocessors at all. Instead, MIPS is purely a design center—an IP (intellectual property) company. MIPS designs CPU cores and then licenses those designs to a half-dozen semiconductor companies around the world who build and sell the actual chips. Thus, there aren’t any chips with the MIPS brand name on them. Instead, you’ll see the NEC, Toshiba, or Philips names, among others. MIPS Technologies collects royalties when these chips are sold, which it uses to fund further processor development.

Although all MIPS processors are software-compatible, each vendor makes its own special chips. No two are exactly the same. Philips and NEC, for example, compete for handheld design wins, even though both companies make compatible MIPS processors.

Intel flexes muscles with StrongARM
The ARM architecture is owned by Advanced RISC Machines in Cambridge, England. Like MIPS, ARM is a pure IP company that licenses its CPU designs to semiconductor manufacturers, who then sell the chips under their own name. Unlike MIPS, however, ARM has about 30 licensees, making ARM processors nearly ubiquitous in the industry.
ARM’s best-known licensee is probably Intel, which only started making ARM processors this year. When Intel bought Digital Semiconductor, it also acquired an outstanding microprocessor family, called StrongARM. The StrongARM chip was a joint effort between ARM’s designers and Digital’s engineers. When the first StrongARM-110 chip was introduced in 1996, it got rave reviews. The SA-110 is fast (up to 233MHz), low-power (about 600mW, on average), and cheap (starting at US$29). The SA-110 was soon followed by the SA-1100, which integrates a 200MHz StrongARM processor with a color LCD controller, memory controller, PCMCIA controller, USB port, IrDA, and interface for a touch screen. In short, the SA-1100 is an Apple Newton 2000 on a chip, and at just US$29–39 in volume, it’s a bargain, too.

The SA-1100 is like the proverbial five-pound bag, and because it’s stuffed with so many features, it’s best suited for high-end, well-equipped systems (like the Newton). At 133–200MHz, the chip is more than fast enough for real-world handwriting recognition. In fact, the SA-1100 would be well suited for voice-recognition systems, too.

AMD maintains its Elan
Microsoft has always said that Windows CE would support several different CPU architectures, but the x86 was well down the list when it came time to get the OS up and running. The x86 chips were late to the party because low-power designers just don’t think of x86 chips as competitive. Born and raised in the PC environment where power consumption is irrelevant, x86 processors are at a disadvantage when it comes to battery life. Besides, 386 and 486 processors are CISC chips—yesterday’s technology—and lack the sex appeal of newer RISC designs.

But one x86 maker has done a lot to reverse those prejudices. While Intel gleefully abandoned its older 386 and 486 (and even slower Pentium) processors, AMD kept right on making these workhorse components, and even developed better, faster chips than Intel did.

Two good examples of AMD’s commitment to the embedded-x86 market are its Elan processors. The Elan400 and Elan410 are basically PC motherboards on a chip, with a 486 processor core and all the PC-compatible I/O to make a complete system.
For pen-based systems, the Elan400 is the most interesting. This chip runs at up to 66MHz; not record-setting, to be sure, but adequate for many needs. The part also includes controllers for an LCD screen, memory, PCMCIA cards, and a keyboard. AMD was smart about power conservation, too, designing the chip to shut off portions that aren’t being used. The PCMCIA controller, for example, draws no power unless it’s active.

The major charm of the Elan410 is its software compatibility. You can’t swing a dead cat without hitting an x86 programmer, and Elan takes advantage of all the combined experience of millions of PC programmers, development tools, operating systems, debuggers, and compilers. Its 486 processor core has been proven through years of hard use, so there should be no surprises in store for the developer.

Motorola and IBM go PowerPC
Sometimes lost amid the shuffle are two PowerPC processors that run Windows CE: Motorola’s MPC821 and IBM’s 401GC. Although they’re both PowerPCs, they couldn’t be more different.

The MPC821 is similar to the StrongARM-1100. It carries an LCD interface, a DRAM controller, and a PCMCIA interface. At 40MHz, the MPC821 offers solid performance, and the chip is reasonably frugal with battery power. It’s a great starting point if you’re interested in PowerPC.

For the AC-powered crowd, there’s IBM’s PowerPC 403GC chip, which was originally designed for television set-top boxes. It includes DMA controllers and serial channels to help with system development. IBM plans a whole series of PowerPC chips based on the 403 and its little brother, the PowerPC 401.

Enter Dragonball
No discussion of low-power processors would be complete without mentioning "Dragonball." Although it doesn’t run Windows CE, Motorola’s 68328 chip is the most popular PDA processor today as the heart of the PalmPilot and Palm III. This modest little processor proves that sometimes slow and steady really does win the race.

The 68328 is based on the 68000, one of the very first 32-bit processors ever developed. The chip got its nickname from the traditional Chinese New Year dragon at the head of the parade, carrying a red ball in its teeth. Dragonball was originally supposed to be used in a pager for the Chinese market, but wound up instead powering Palm Computing’s popular Pilot.

At first glance, the 68328 is not impressive. Its little 68000 heart beats at just 16MHz, so its performance is nowhere near that of the other processors. But the chip includes its own LCD controller, power management, and serial and parallel I/O pins. With the addition of an inexpensive digitizer, Dragonball is ready for action.

HPC roundup
The first NEC MobilePro and Philips Velo handheld PCs were all based on MIPS processors. NEC, naturally, used its own microprocessor, called the VR4101. Likewise, Philips used its own 31500 processor.

The other four HPCs from Casio, Compaq, LG, and Hewlett-Packard all used Hitachi SuperH processors. (Actually, the Compaq HPC was just Casio’s Cassiopeia with a Compaq label on it.) The first three units were based on the SH7708, while the HP 320LX used a slightly different SH7707 chip and had a wider LCD screen.

Of these six HPCs, the Velo is the fastest, sprinting ahead of the MobilePro by about 25%. Close behind is the Cassiopeia, a mere 5% behind the NEC unit.

The Velo had a speed advantage from the start. The 31500 processor in the Philips unit runs at 36MHz, edging out the 33MHz VR4101 chip in the NEC MobilePro. But that alone isn’t enough to make a noticeable difference. After all, the SH7708 processor in the Cassiopeia runs at a comparatively frisky 60MHz. What helps the 31500 most of all is its integrated LCD controller. You see, by including the LCD controller on the chip, Philips was able to speed up accesses to the screen. The NEC and Hitachi chips, in contrast, need a separate, off-chip LCD controller, which takes longer for the hardware to update.
The 31500 also has a larger instruction cache than the VR4101 (4K vs. 2K) and a wider, 32-bit bus interface to external memory. Taken together, these features make the 31500 noticeably faster than the VR4101, but also more expensive. The Philips chip sold for US$39, compared with US$25 for the VR4101, until recent price reductions.

On the plus side, the NEC processor includes all the analog-to-digital (A/D) and digital-to-analog (D/A) circuitry on the chip, which Philips and Hitachi leave off. Either way, you’ll need extra circuitry to make a complete PDA: an LCD controller for the NEC part or D/A and A/D converters for the Philips device. Or both for the Hitachi processor.

Although the Philips approach provides faster screen updates (which users perceive as higher performance), NEC defends its no-LCD approach. By leaving off the complex (and expensive) LCD controller, the NEC chips are suitable for systems that don’t need a display. The VR4101 can be used, for example, in bar-code scanners, printers, and portable devices.

So, what’s interesting about the Cassiopeia? The SH7708 has the fastest clock rate, but it fell behind the VR4101 by about 30% in performance tests. Two words: code density. The Cassiopeia uses only half as much memory (2 Mbytes of RAM and 4 Mbytes of ROM) as either the Velo or the MobilePro, yet all three units sell for about the same price. That 6 Mbytes of cost saving goes straight to Casio’s bottom line.

RISC: The next generation
Before too long, all three of these chips were updated. The original VR4101 was replaced by the VR4102, and then by the VR4111, which improves on the original in a lot of ways. The VR4111 has a wider, 32-bit bus to access external memory and its clock speed was upped to 100MHz. To support the faster clock rate, the instruction and data caches grew to 16K and 8K, a healthy 8x increase in size. Even with all these improvements, power consumption actually fell by about 35%, to just 180mW (typical), thanks to a more aggressive 0.25-micron semiconductor process. The price held steady at US$25. On the downside, the VR4111 needs a 2.5-V power supply, which some designers find difficult to work with.

Philips improved on its 31500 with the 31700, which replaces the monochrome LCD controller with one for color LCD screens. Its maximum clock frequency nearly doubled from 40MHz to a respectable 75MHz. And, the new chip’s power consumption actually went down, averaging about 290mW, due to a switch to a more modern fabrication process.

Hitachi’s SH7709 ups the speed of the SH7708 to 80MHz. The new chip also comes with a DMA controller and A/D functions like NEC’s device. For PDA designers, Hitachi also offers a companion chip, the 64461, that includes an LCD controller and an interface to either PC Cards or Mini Cards. Hitachi sells the pair for US$70.

Although it wasn’t used in the first wave of Windows CE devices, Toshiba’s R3912 was one of the first MIPS chips to actually run the operating system. The newer R3922 is basically a speed upgrade—albeit a big one—from the R3912. The R3922 runs at a speedy 166MHz, making it one of the faster Windows CE processors available. To keep the chip running at that speed, the caches got much larger (16K for instructions, 8K for data); in fact, the chip’s silicon is about 75% cache by area. A new PCMCIA controller was also added to the R3922. At about US$35 in volume, Toshiba’s R3922 is a speedy performer for the price.

High power, high end
For higher-end Windows CE devices that don’t necessarily have to be portable, there are a number of even faster, more powerful chips.

NEC’s low-power VR41xx chips are complemented by the high-end VR4300, ’05, and ’10 processors. These chips run at 100 to 167MHz and have full floating-point math units. The VR4300 is hugely popular as the heart of the Nintendo 64 video game. Although their power consumption is a bit high (over one watt) for handheld applications, these chips deliver terrific price/performance, at less than US$20 in quantity.

Also heading into video games is Hitachi’s new SH7750 microprocessor, which is used in Sega’s Dreamcast. Like the VR4300, the 200MHz SH7750 has a floating-point unit, but it also includes interesting new 3D matrix-transformation instructions that should add to Dreamcast’s appeal. And, since it will run Windows CE, Dreamcast may be able to share games with PCs.

Looking ahead
In this industry, the future is always predictable: more, better, faster. All of the major processor vendors are updating their product lines, looking for a competitive edge. For example, every vendor is moving to more advanced process geometry, which will make their chips smaller and faster. As a side effect, these chips will have to run on lower voltages, which has the nice benefit of lowering power consumption, extending battery life, and reducing heat. Chips built in 0.25-micron processes are just coming out now. Look for 0.18-micron chips that run on less than two volts in 1999 and 2000.

Many vendors are also integrating DSP (digital signal processing) features into their chips so that they can perform modem and wireless telephone functions essentially for free. Many odd combinations of CPU and DSP are due to appear later this year.

With performance improving so rapidly, exotic features like voice recognition and synthesis aren’t far off. Already, chips that do this are in the works. The problem is reducing their power consumption to reasonable levels. Intel has begun development on a new generation of StrongARM chips; if it is as impressive as its predecessor, the chip giant may yet become a force in this market.

Whatever the outcome, it’ll be fun to watch. Desktop computers may get all the attention, but embedded applications, such as handheld devices and consumer electronics, are driving innovation, not PCs. Power demands are driving chip designers to be creative with circuit design, and the inexorable advance of semiconductor manufacturing lends a hand by pushing voltages down and slashing power consumption. Consumers dollars are a big incentive and handheld, wireless, and portable electronics have a strong appeal in the marketplace. At this rate, one can only imagine what wonders the handheld devices of next year will hold. -

Jim Turley is the Senior Editor of Microprocessor Report and Editor in Chief of Embedded Processor Watch. For a free subscription to the latter, send email to join-embedded@ Jim is an industry analyst, speaker, and writer covering microprocessor chips and embedded hardware. He is the author of six books, is regularly quoted in the business press, and makes frequent appearances on television, radio, and at industry conferences.

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