Re: [SystemSafety] Stupid Software Errors [was: Overflow......]

From: Jensen, Martin Faurschou < >
Date: Tue, 5 May 2015 07:43:26 +0000


I remember an old professor teaching me (or at least trying to), embedded software design many years ago. He was claiming that, any value that we expected to count upwards on regular intervals, should be initialized, not to zero, but to a value slightly below its maximum. He indeed believed that this would save us from much grief later on, as our bad design would then show up rather early...

With best regards,
Martin Faurschou Jensen

Siemens A/S
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Siemens A/S. Headquarters: Borupvang 9, 2750 Ballerup, Denmark. Tel: +45 4477 4477 CVR-no. 16 99 30 85 -----Original Message-----
Sent: 5. maj 2015 09:29
To: Peter Bernard Ladkin
Cc: systemsafety_at_xxxxxx Subject: Re: [SystemSafety] Stupid Software Errors [was: Overflow......]

Peter,

On 2015-05-05 09:03:31 +0200, Peter Bernard Ladkin wrote:
> After fifty years of programs not handling date and time correctly,
> even according to their own requirements, including the single most
> expensive anomaly in history coming in at well over $300bn, it surely
> requires heroic nonchalance to suggest
>
> > .... this is a non-issue.

I've also seen my fair share of time/date problems, including the impending Year 2038 bug (which no-one seems to be worrying much about).

I also notice that 248 days is pretty well exactly the range of a 32-bit signed integer incremented as 10ms intervals. So this is quite emphatically *not* a time/date issue, but an uptime issue.

Many control systems have specified maximum uptimes. They often rely on checks and tests performed at startup or shutdown to detect latent hardware failures. Destructive RAM tests are a prime example of things that cannot be done properly during operation.

I also notice that the press reports state that the systems "shut themselves down", not "crash", which implies (to me at least) that there is at least some error detection and handling going on.

So, in the absence of any detailed technical information about the requirements, design, implementation, service documentation, operational manuals etc. about these systems, I stand by my opinion until facts emerge that prove me wrong.

There are worse things to worry about.

Dave

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David Haworth B.Sc.(Hons.), OS Kernel Developer    david.haworth_at_xxxxxx
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Received on Tue May 05 2015 - 09:43:35 CEST

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