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Toyota Case: Single Bit Flip That Killed

10/25/2013 03:35 PM EDT
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DrQuine
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Dead man Controls?
DrQuine   12/14/2013 10:08:44 PM
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One way to carry the passive concept a step further would be for the "dead man switch" to invoke braking rather than merely releasing the throttle.  I believe that already exists in trains. The challenge in cars is that we have have two controls: the throttle and the brake rather than a single control that when released would return the car to a statioary condition. We also have to be careful about stopping too quickly if the surrounding traffic isn't following suit. As a minimum the "dead man switch" would do well to provide some external indication that the car is stopping. Currently releasing the accelerator does not cause the brake lights to illuminate.

ScottDeaver
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Re: Single bit flip
ScottDeaver   12/11/2013 3:39:05 PM
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One of the challenges in automotive software design is fail-safety. Ideally, you want the failure fallback to be at minimum passive, at best natural - that is, you want the path of least resistance upon failure to result in the safest outcome. That's not such a big problem with acceleration - if the driver has a heart attack, then (in most cases) his foot relaxes from the accelerator and the car at minimum won't go faster and will ultimately slow to at least idle speed. The natural course of events happens to be the best one for safety, and requires no additional effort to invokde (in other words, it is passive). Obviously, active subsystems could be applied to the situation to improve safety - invoking the brake, for example - but the natural behavior contributes to, rather than detracts from, safety.

Braking is an entirely different problem. First, because of legacy mechanical designs in cars, braking is not a passive behavior - you have to DO something. Consider that one of the scenarios in which braking would be invoked as a fail-safety measure would be in the event of system power failure. Where would power come from to depress the brake? Where would power come from to feed the electronics to compute the need to depress the brake? Complicating the issue is the fact that many power brake systems are vacuum-assisted - vacuum that goes away when the engine stops, markedly altering the amouint of pressure needed to activate the braking system. In hybrids, this is further complicated by hardware and electronics that attempt to tap the residual and excess energy being thrown off during braking.

Electric cars can be made significantly more fail-safe for braking, because the electric motors used are also generators when the stator is not being powered (and generators cause drag).

The best solution for the problem is simple, but requires a re-design of legacy technology. That solution proposes electronically-regulated electric clutching at the drive wheels, where unless all systems throughout the vehicle are optimum no forward power is allowed to pass through to the wheel, and when not expressly powered to go forward the braking systems are by default engaged.

I've been professionally writing software for thirty years, and there is no code I can imagine that could be deployed to solve the issue through electronics alone that wouldn't have bugs, and therefore fail under some condition.

 

junko.yoshida
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Re: Single bit flip
junko.yoshida   11/28/2013 1:39:17 AM
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@ARabold, thanks for chiming in. 

I will definitely look up Nancy Leveson's book. Much appreciate your tip.

junko.yoshida
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Re: inherently safe design of automobiles
junko.yoshida   11/28/2013 1:37:23 AM
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@Mervynrs, an intersting argument -- sort of coming from the left field.

And yet, somehow I don't agree that the "speed" is the key reason for safety issues of cars. A growing list of all the bells and whistles now added to cars seems to be the cultprit in my mind, although some of those new features are being developed for safety reasons.

Mervynrs
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inherently safe design of automobiles
Mervynrs   11/27/2013 5:20:26 PM
As a complete departure from the current approach to automotive safety system inprovement by computerisation, I would like to pose the following question?

Why are regular automobiles designed and built with the capabilty to move at speeds that all agree can cause lethal harm? If the engines were all "governed down" there may well be no need for most of the layers of safety system architechture in the first place! 

The presence of speed limit laws in all nations is admission that we all know what the dominant risk factor is. So why not fix it at the source?

ARabold
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Re: Single bit flip
ARabold   11/20/2013 9:55:45 AM
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There is an extensive literature on the question 'how safe is safe enough', and you might start with the early chapters of Nancy Leveson's book 'Safeware: System Safety and Computers' (though it is somewhat dated, and she has a new book in the works.)

Forcing a hardware / software dichotomy on the safety question is unwise, as a significant subset of risk involves aspects of both domains, and their interaction. 

One issue is 'what are the alternatives?' In the case of anti-lock braking, we add a system that could potentially interfere disastrously with braking, but which, when it works, reduces the frequency and severity of accidents. In the case of a car's throttle, I don't know if there are any compelling reasons for full-authority digital control, from a safety perspective.

It is well established that redundancy can effectively mitigate random physical errors to the point where it is no longer the dominant risk (it is not, however, effective for software errors, as different developers tend to make related mistakes, so the errors in independently-developed implementations of the same requirements tend to be somewhat correlated.)

You quoted Larry comment, "If you look at modern automotive control systems, they are beginning to introduce redundant voting controls" (emphasis added.) This suggests, disturbingly, that the designers of automotive control systems are far behind the state of the art with regard to digital systems safety.

 

 

ARabold
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Re: Single bit flip
ARabold   11/20/2013 9:06:11 AM
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I don't know if you replied to my post by mistake, but nothing in what I wrote could be properly construed as indicating that I doubt the potential lethality of some software, or that I doubt it has actually happened. I read Nancy Leveson's highly informative report on the Therac-25 when it was first published, and I was appalled by the fact that the development of this safety-critical software was entrusted to an unqualified person, and deployed without effective rik analysis, review and testing.

This quote should have made my position clear:

 "These risks can be effectively mitigated, if and ony if you make a serious effort to do so." (emphasis added.)

Effective mitigation does not mean 'eliminate all risk' for software any more than it does for any other technology.

 

KGround
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Re: Single bit flip
KGround   11/18/2013 2:42:16 PM
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You question that a software bug can kill ??

There are many, many examples. Here:

http://en.wikipedia.org/wiki/Therac-25

is one of my favorites.

We trust machines with our lives every day, and that is fine, but we should also remember that a machine is heartless and relentless and will kill you in the blink of an eye if it gets the chance (and this applies to simple mechanical equipment as well as complex software driven systems), it will feel no regret later, and suffer no consequences. 

Trust your life to a machine if you wish, but it should be conscious decision and not just force of habit.

ARabold
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Re: Single bit flip
ARabold   11/4/2013 9:45:11 AM
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Frank Eory wrote:

"It makes one wonder how blame can be attributed to software in a system in which the source of the error may have been a random SRAM bit that was flipped by an alpha particle or other natural radiation event."

If that were an unavoidable problem, the undavoidable conclusion would be that digital equipment is unsuitable for safety-critical purposes, especially for things such as a car's throttle, where mechanical linkages have worked well for decades, and so where it's particularly hard to make a case for any additional risk.

The point here, however, is that these risks can be effectively mitigated, if and ony if you make a serious effort to do so. If you are unable or unwilling to do that, do not use digital electronics where peoples' well-being is at risk.

"Is the failure being blamed on software, or is it an overall laxity of hardware plus software..."

None of the above. The blame is being placed on the people of Toyota who, in their complacent ignorance, failed to take reasonable steps to reduce the risk.

I find Mr. Eory's "things break, that's just the way it is" attitude disturbing. No-one with that attitude should have any responsibility in the development or deployment of safety-critical systems, or the policies that govern their use.

 

 

Antony Anderson
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Transcript of evidence
Antony Anderson   11/1/2013 5:47:47 PM
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Dear Mark,


e-mail me and I might know of someone who could help you

Antony Anderson

e-mail: antony.anderson@onyxnet.co.uk

Tel +44 191 2854577

website:www.antony-anderson.com

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