This article was published in the February 2015 issue of Maximum PC. For more trusted reviews and feature stories, subscribe here.
Slimming down for the Internet of Things
Over the past months, I've described two of the world’s most powerful microprocessors in this column. But chip makers aren’t always thinking big. Some of the most surprising new designs are in the smallest processors—particularly for wearable devices and the Internet of Things (IoT).
Smart watches and Google Glass are only the first examples of wearables. Expect many more, including physical implants. IoT devices include everything from smart thermostats and smoke alarms to industrial machinery and car navigation systems. Processors for these gadgets share three requirements: they must be small, consume very little power, and provide wireless connectivity.
On-chip radios should solve bad battery life in wearables.
The obvious solution would seem to be microcontrollers, which have been around for decades. On a single chip, MCUs integrate a CPU core, SRAM, nonvolatile memory (usually fl ash), and peripherals. Those peripherals typically include counters, timers, analog/digital converters, and digital/analog converters. Some even have USB or Ethernet controllers. Essentially, an MCU is a single-chip computer that can function without external DRAM.
But MCUs lack one crucial feature—wireless connectivity. For that, they need external radio chips. And those additional chips consume more power and board space, which are scarce resources in wearables and IoT devices. Although some early gadgets use conventional MCUs, we need new processors that add wireless to their bag of tricks.
They’re coming. One example is Marvell’s new 88M processor family. The fastest chip has a 200MHz ARM Cortex-M4F core. With 512KB of SRAM, it doesn’t need external DRAM to run a small OS and simple software. More important, this chip has an 802.11n Wi-Fi radio. Two similar models add flash memory and replace the Wi-Fi with either a Bluetooth or Zigbee transceiver. Designers can build a working system by adding only an external crystal and antenna. Total cost for this combo: about $10.
Marvell’s tiny processor sips mere milliwatts of power, but it’s still not small enough for some things. That’s why French firm Cortus recently introduced a 32-bit CPU core with an abbreviated three-stage instruction pipeline. By contrast, Intel’s Haswell processors have up to 19 stages. The Cortus APS23 is about the same size as ARM’s smallest core, the Cortex-M0+, which has a two-stage pipeline.
To beat that, a Slovenian company recently astonished a Silicon Valley conference by announcing a CPU core that has no pipeline at all. (This is like showing up at an automotive industry conference with a one-cylinder push-valve engine.) Beyond Semiconductor’s new BA20 is almost a throwback to the ‘70s, except it’s a real 32-bit processor. Stanford University, meanwhile, has prototyped an ant-sized processor that uses so little power it harvests what it needs by absorbing radio waves.
Another challenge is shrinking the transceivers and antennas. An IoT processor may need radios for Wi-Fi, cellular, Bluetooth,
Zigbee, GPS, or near-fi eld communications (NFC). Some of those require multiple radios—Wi-Fi operates in the 2.4GHz and 5GHz bands, while cellular networks use many different frequencies. This challenge is more difficult than making tiny CPU cores because analog circuitry doesn’t shrink as neatly.
Nevertheless, the race is on to build smaller, cheaper, more power-efficient IoT processors. Before they mature, we’ll have to tolerate inconveniences, such as bulky smart watches that require daily charging. But remember, the first cell phones were as large as World War II walkie-talkies.
Tom Halfhill was formerly a senior editor for byte magazine and is now an analyst for Microprocessor Report.
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