Talk About Quality

Tom Harris

The Day they Broke the Lever

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We may never know all the details of the recent Toyota failures, because, unlike the Challenger and NASA, Toyota is a commercial entity rather than taxpayer-funded government. And it’s a bit early to be looking for definitive analysis. What we can do, as embedded software developers, is realize what we’re up against, and how it didn’t start yesterday.

When microprocessors first came out the buzz on the news was that soon they were going to be inside everything. I remember wondering what do we need them in everything for? My washer and my microwave oven, for example, worked just fine with a mechanical dial. But I was wrong and now they are in everything.

Much earlier on, complex systems were based on the Six Simple Machines. I can’t say which is simplest, but maybe it’s the lever. What’s important here is that the behavior of the lever is governed by physical properties of solids, which by now are pretty well understood. Push down on one end, and the other end goes up. Exceptions exist: solids can stretch under tension, deform under pressure, and if you push too hard, they can break. Apparently Toyota had problems with this too, in their gas pedal problem and fix.

Technical advances brought hydraulics — based on the properties of fluids and gases. I also remember replacing a brake line on an old car once, and getting to see how a leak in the line leads to spongy braking, and, if I hadn’t been refilling it weekly before the replacement, to brake failure.

In both of those technologies, the basic idea is that the system user (e.g. the driver) pushes on the control, force is transmitted immediately through a physical medium, and the desired effect occurs. Failure modes are well understood and (usually) are prevented.

Now replace the lever with software. No more physical properties: the behavior of the software transmission line is governed by the behavior of people — software developers writing lists of instructions which are translated several times before reaching the hardware. Now you push on the control, and a cacophony of instructions (okay, I’m being unfair — if the software is well-written, it’s a concert of instructions) rush down a wire to an actuating motor at the other end.

Let’s be clear about this: real-time software is a myth. The metal of the lever, or even the fluid of the hydraulic line, has been removed and replaced by your entire software development organization. Materials science out the door, organizational sociology in its place. If you want to know where that leaves us, read this short post about drive-by-wire, and the many comments there.

What’s the answer? In the code itself — perhaps it’s avoiding interrupts and multi-threading, and moving to synchronous programming where everything proceeds in lock-step. At least then a modern car would run like clockwork. Other than that, notice that many of the suggestions in the discussion talk about mechanical back-up systems, which are basically putting the lever back into the system.

But software development is not, as commonly believed, about technology. It is about writing, reading, and communication in ever-larger groups. Those who have said, “The pen is mightier than the sword” were thinking of politics. Now writing, in the form of software, interposes itself between every hand and hammer. We have┬ábroken the lever; do we know how to wield its replacement?


Written by Tom Harris

February 13, 2010 at 11:27 pm

Posted in Technology and Society

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