Motoring with microprocessors

August 11, 2003

Jim Turley-August 11, 2003

Thanks to the magic of microprocessors and embedded systems, our cars are becoming safer, more efficient, and entertaining.

"I'm drivin' in my car. I turn on the radio." — Bruce Springsteen, "Fire"

By my estimates, the average middle-class American household includes over 40 embedded processors. About half are in the garage. Cars make a great vehicle (sorry) for deploying embedded processors in huge numbers. These processors provide a ready source of power, ventilation, and mounting space and sell in terrific quantities. Besides, they're cool. Better still, automotive processors add sexy high-profile features that car buyers will pay for. Processors provide better profit margins than leather seats, undercoating, or "convenience lighting groups."

How many embedded processors does your car have? Go ahead, guess. If you've got a late-model luxury sedan, two or three processors might be obvious in the GPS navigation system or the automatic distance control. Yet you'd still be off by a factor of 25 or 50. The current 7-Series BMW and S-class Mercedes boast about 100 processors apiece. A relatively low-profile Volvo still has 50 to 60 baby processors on board. Even a boring low-cost econobox has a few dozen different microprocessors in it. Your transportation appliance probably has more chips than your Internet appliance.

The statistics are startling. New cars now frequently carry 200 pounds of electronics and more than a mile of wiring. Processors and their peripherals have squeezed into the side- and rear-view mirrors, wheel rims, headliner, gas tank, seat cushions, headrests, bumpers, and every other crevice of a modern car. Dashboard electronics such as the radio, air conditioning, and satellite navigation system are just the obvious ones. Even more MIPS and MHz are lurking under the surface.

The first car to use a microprocessor was the 1978 Cadillac Seville. The chip, a modified 6802, drove the car's "Trip Computer," a flashy dashboard bauble that displayed mileage and other trivia. Today that kind of microprocessor muscle could barely adjust your mirrors.

Highway network
Networks have also come to automobiles. Among the popular standards are J1850 and CAN, with the latter gradually replacing the former. Interprocessor networks are designed to cut down the long, tangled, complicated, expensive, and heavy wiring harnesses that permeate cars today. Networks, of course, also enable processors to communicate amongst themselves. The results are intended to be smarter, safer, lighter cars with simpler and more reliable wiring. In the process, automotive engineers with time on their hands have created a number of peculiar features to crowd a car's list of options.

For example, the radio on many cars talks to the automatic transmission over an in-car network. Why? So the radio can automatically adjust its volume in relation to road noise (which is a function of speed). The airbag accelerometer, parking lights, GPS navigation, cell phone, and door locks also network so that in a serious accident, the car calls for emergency aid, sends the GPS coordinates of the accident, unlocks the doors, and flashes the car's lights. Side mirrors get a cue from the transmission so that when the driver shifts into reverse, the mirrors bend down and inward, the better to provide a view of what you're backing into.

This last feature was removed from a number of cars after thieves discovered that breaking off a mirror provided convenient access to the car's control network, including commands to unlock the car. (They could have just as easily reprogrammed the radio presets or reclined the passenger seat, but that's much less profitable to car thieves.)

Many cars use a combination of the older J1850 network and the newer CAN network (not to mention ISO 9141, SCP, DDB, and others). Both are useful for drivetrain (engine and transmission) applications as well as safety features. Both buses provide low-latency, predictable performance, but neither is well suited to the high-bandwidth needs of toddlers in the backseat. Minivans with DVD players and video games are adopting a separate "fun bus" for video and audio transport within the vehicle. FireWire and Media-Oriented Systems Transport (MOST) are two contenders, with most European automakers favoring the fiber-optic MOST.

Fun to go
The fastest growing segment of car electronics is devoted to entertainment or information, the so-called "telematics" business. An extreme example is BMW's controversial iDrive, an eight-way joystick mounted on the armrest of new 7-Series cars. After careful study, an alert and undistracted driver can, with only six clicks and twists of the knob, change the radio station.

Safety features come in second behind telematics. Antilock brakes have been microprocessor-controlled for years; now the brakes themselves can be computer controlled. Mercedes-Benz offers Brake Assist, a system that decides when the driver isn't pressing hard enough on the pedal and creates its own panic stop. The system is said to shorten emergency stops by a significant amount, but also makes the car difficult to drive smoothly in slow traffic.

Processors will soon tell us when our tires need air. The U.S. government has decreed that all new cars must have tire-pressure sensors. This follows a recent debacle in which several dozen drivers neglected to keep their SUVs upright and then blamed the tire and vehicle manufacturers for their own failure to keep air in the tires. Henceforth, cars will have sensors mounted to the metal wheel rims and an "idiot light" on the dashboard saying it's time to top up the O2. A technology solution by fiat, you might say.

New lane-departure warnings may supplement the venerable Botts dots. An image-sensor system from Iteris looks for painted stripes and other lane markings. If it feels the driver is about to wander across the lane (and possibly into oncoming traffic), it sounds a warning. Detecting lane markings is hard enough, but the real problem is distinguishing deliberate lane changes from unintentional ones. Intersections and corners are treated as deliberate changes of direction. A turn signal also disables the warning. Of course, that effectively renders the system useless on one side of most Cadillacs in Florida where turn signals are in permanent blink mode.

Gearing up to hit the road
What does it take for a chip to make it in the automotive market? Longevity, for one. While PC product cycles are measured in weeks or months, embedded processors for cars need to be around for five to ten years, minimum. Not many chip companies can commit to producing the exact same part for that long, so many worthy CPUs never find their way into your driveway.

Extended temperature ranges are also vital. Motorola rates its automotive-grade PowerPC 5200 from "40C to +85C. And that's just for dashboard and interior use. For under-hood applications, the chips run reliably at 105C, albeit at reduced clock frequency. You could literally fry an egg on top of the chip.

Under-hood systems aren't limited to just drivetrain control. Plenty of navigation systems, collision-avoidance systems, and even radios are actually located in front of the firewall, near the engine. Space under the dashboard is at a premium, and airbags, gauges, and LCD screens get first dibs on that prime real estate. Everything else is pushed forward (or upward, between the roof and the headliner) and connected to the dashboard switches via the network. Thus, even radio receivers might have to be high-temperature rated.

Caches are taboo for automotive processors, especially those controlling the drivetrain. Caches lead to unpredictable or nondeterministic performance, a no-no for valve timing, brake control, or ignition management. Automotive processors today (including PowerPC and other RISC architectures) have no caches, but chip developers are cooperating with automotive programmers to find ways to work around caches' unpredictability. New replacement algorithms and line-locking schemes may soon appear.

Power would seem to be no problem in an automotive environment—even the wimpiest 80-horsepower engine generates almost 60,000 watts. But no. While electrical current itself is no problem, the excess heat it generates is. All microcontrollers generate some heat; a 32-bit RISC chip can easily draw five to six watts. (AMD's Athlon 3200+ consumes 76W.) That kind of thermal energy is hard to dissipate from a cramped dashboard, engine bay, or roof-mounted console. Two watts is now considered the outside of the thermal envelope. Ironically, forced-air cooling isn't available because all electronics have to be sealed in watertight enclosures.

High volume is also key. No automaker wants a chip that's in limited supply, and chip makers are naturally happy to oblige them.

At the low-volume end of the market, the Williams Formula 1 team uses Xilinx FPGAs with embedded PowerPC processors in its racecars. Although the team is understandably hesitant to say much about its onboard electronics, they will say the chip looks after the car's sequential transmission, traction control, and launch control (for race starts).

Today and tomorrow
Other applications abound. Jaguar and others offer station-keeping cruise control that holds your distance from the car in front. Backing a Mercedes S-class into a parking space lights a sequence of indicators to show how much room you have left, like docking a cruise ship. BMW air conditioners have separate front/rear settings and even different left/right settings. Volvo ignition keys hold personal settings, such as seat and mirror positions and radio presets, in flash memory. DSP processors handle echo cancellation and voice recognition for hands-free cell phones. They also crunch GPS data and do voice synthesis (for spoken directions), MP3 playback, AM/FM decoding, and more.

As often as not, analog gauges aren't really analog. A stepper motor controlled by a microprocessor spins the dials. Usually one processor controls half a dozen different steppers, which is enough gauges for most cars.

The list goes on. New BMWs cut the steering column in half, interposing motor and planetary gears to tweak steering "feel" at different speeds. Air bladders are replacing springs and shocks to give continually adjustable ride height and firmness. Headlights angle into corners. Side mirrors fold themselves flat for parking on narrow European streets. Rain-sensing windshields turn on the wipers automatically. Brake systems lightly engage the brake pads periodically to wipe away moisture. Even the humble parking brake (either as a lever on the center console or as foot pedal) has been replaced by an electronic version that engages itself when the key is removed and releases itself when the car is put in gear. So much for flamboyant handbrake turns.

What does the future hold? Pretty much anything you can think of. A few automotive OEMs are developing in-car cameras to judge the presence, weight, and position of occupants for best airbag deployment. (Combined with wireless or cellular access this could create a strange webcam privacy issue—or a mixed blessing for parents with teenagers.) Microprocessor-controlled solenoids may soon replace cams and valve lifters. An Italian company is developing rearview mirrors with image-recognition that sense impending rear-end collisions. In-car Bluetooth or 802.11 access points might up- and download MP3 tunes every time you "dock" your car in the garage. Motorola, the company that invented car radio, is about to make it a two-way medium. Listeners will be able to click their car radio button to buy the CD that's playing or get a discount from a nearby (as determined by GPS) burger joint. Radio ads will gain the "click through" tracking ability that makes Web banners so useful to advertisers.

Our cars are easily the most wired and technologically advanced devices we own, and more development is just down the road. It's been twenty years since the first electronic systems began replacing critical mechanical components. The easy stuff is done. We're well into the optional, exotic, gee-whiz phase now. It's hard to argue against modern safety features—antilock brakes and traction control, for instance—but I wonder how many other new features will turn out to be counterproductive. Will we see an equal but opposite reaction toward relatively low-tech cars, like the people who prefer vacuum tube amplifiers? Or will tomorrow's drivers become dependant upon electronic nursemaids to find their way to the grocery store?

We smile at Grandpa's recollections of cranking up the Tin Lizzy. Will our grandchildren believe our yarns about steering a car?

Jim Turley is an independent analyst, columnist, and speaker specializing in microprocessors and semiconductor intellectual property. He was past editor of Microprocessor Report and Embedded Processor Watch. For a good time, write to jim@jimturley.com.

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