Embedded Systems November 2000 Vol13_12

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Page 29 of 189

irst: Avoiding ware Mishaps Hc<;ment:~> happen. That's just part of life. But when mission- ol· safe~ critical systems experience failures due to faulty softw · serious questions a~e rai d. e, espite the risks, software is increasingly making its way into mis ion- and safety-critical embedded devices. This article explores the challenges inherent in balancing the tremen- dous flexibility and power provided by embedded softwat-e against the risks that occur when software failure leads to loss of life or property. This article also explores the root causes of several famous embedded software failures, including the Therac- 25, Ariane 5, and recent failed Mars missions. The problem of safety Life is full of risks. That much is obvious. And most risks can be avoided if the cost of avoidance is acceptable. We can avoid ever being involved in an automobile accident simply by never traveling by car. Well, that works for drivers and passengers, but sti ll doesn't necessarily help pedestrians. For pedestrians, avoiding any possibility of automobile accident would involve staying close to home a great deal of the time, and strictly avoiding side- walks, driveways, and curbs-not a particularly palatable set of choices for most of us. And so we learn to live with the inherent risks that surround us, because the cost of avoidance just seems too high. However, as technology becomes more and more ubiquitous, with more of that technology being controlled by software, a greater portion of the risk we face is ultimately in the hands of software engineers. Most of the time, the risks we face don't bear fruit. But when they do, we call the event an accident or a mishap. The kinds of accidents we're pri- marily concerned with in this article are the type that lead to pe rsonal 28 NOVEMBER 2000 Embedded Systems Programming

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