Low-power processors for Windows CE
A discussion of current proccessor technology (October 98)
Which is more important, size or sex appeal? Thats 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. Lets 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.
MIPS comes from multiple sources
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.
The SA-1100 is like the proverbial five-pound bag, and because its stuffed with so many features, its 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
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 AMDs 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.
The major charm of the Elan410 is its software compatibility. You cant 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
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. Its a great starting point if youre interested in PowerPC.
For the AC-powered crowd, theres IBMs 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.
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 Computings popular Pilot.
The other four HPCs from Casio, Compaq, LG, and Hewlett-Packard all used Hitachi SuperH processors. (Actually, the Compaq HPC was just Casios 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 isnt 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.
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, youll 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 dont need a display. The VR4101 can be used, for example, in bar-code scanners, printers, and portable devices.
So, whats 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 Casios bottom line.
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 chips power consumption actually went down, averaging about 290mW, due to a switch to a more modern fabrication process.
Hitachis SH7709 ups the speed of the SH7708 to 80MHz. The new chip also comes with a DMA controller and A/D functions like NECs 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 wasnt used in the first wave of Windows CE devices, Toshibas 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 chips silicon is about 75% cache by area. A new PCMCIA controller was also added to the R3922. At about US$35 in volume, Toshibas R3922 is a speedy performer for the price.
High power, high end
NECs 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 Hitachis new SH7750 microprocessor, which is used in Segas 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 Dreamcasts appeal. And, since it will run Windows CE, Dreamcast may be able to share games with PCs.
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 arent 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, itll 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. -
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