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By Jack Ganssle
Succumbing to a bit of techie lust I recently bought a new laptop, a Sony Vaio that uses a 1.7 GHz Intel Centrino chipset.
Now I can't wait for winter.
The bottom of the machine warms up like an old-fashioned vacuum tube. and then continues to heat. until it glows a faint cherry red!
That's just a bit of an exaggeration, but the heat radiated by this machine is nothing short of astonishing. Curious, I hunted around Intel's web site and found the Centrino databook (ftp://download.intel.com/design/mobile/desguide/25261403.pdf). The processor sucks up to 26 amps at a bit over 1 volt. Worse, power requirements fluctuate wildly over the course of microseconds, turning the power plane into an RF circuit if not designed with excruciating care. Nearly 10% of the data book's 372 pages are devoted to practical advice about getting power to the chip.
The company's Xeon CPU gets fabulous performance by prodigious power consumption. It can require 120 amps just for the processor chip!
That's practically enough to start a car. Or to arc weld thin metals.
EDN's May 13, 2004 issue contains a graph (http://www.edn.com/contents/images/415105f1.pdf) that shows Pentium power densities within an order of magnitude of that of the core of a nuclear reactor!
Companies running racks full of Pentium servers have a compounding problem. According to HP (http://computerworld.com/databasetopics/data/datacenter/story/0,10801,105767,00.html) a big server room can consume $1.2 million in electricity every year. With energy, particularly oil, becoming scarcer and more problematic (I highly recommend the book "Winning the Oil Endgame" by Amory B. Lovins, et al for practical solutions to this problem) it seems rather wasteful to turn so much power mostly into heat.
Raw compute horsepower provided by high clock rates and billions of transistors speculatively executing deeply pipelined instructions buried in multi-level cache memories inevitably (today, at least) requires lots of watts. Old timers will remember the days when CMOS logic was nearly a joke, suitable only for low-speed micropower applications running at funny voltages. But increasing power densities doomed bipolar logic; ironically today CMOS rules the digital world as the heat generated by a billion bipolar transistors would initiate a fusion reaction.
Once upon a time an embedded system was an app using a low-end processor. Today we stuff Linux and Windows into devices that are clearly embedded. The distinction between the desktop and embedded is somewhat more blurred than of yore. But perhaps low power consumption is one distinguishing property of most embedded applications.
Cell phones which contain a pair of 32 bitters run for a week or more on a single battery charge. Miserly instruments monitor environmental parameters for years on a pair of AAs. Mars rovers operate motors and computers from feeble solar energy.
What about your products? Do they suck power from a fire hose or sip microwatts?