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Re: Safety-Critical Software Design

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On 16-07-17 07:57 , Randy Yates wrote:
> Hi Everyone,
>
> Are there any formal requirements, guidelines, or recommendations for
> software which will run in a safety-critical environment in the United
> States or world-wide?

Several, of course.

> By a "safety-critical" environment I mean an environment in which a
> failure can lead to loss of, or serious injury to, human life. For
> example, automobile navigation systems, medical devices, lasers, etc.
>
> I know there is the MISRA association and MISRA C. I am wondering if
> there are others.

One starting point is IEC 61508, https://en.wikipedia.org/wiki/IEC_61508.

> My gut and experience tells me there should NEVER be software DIRECTLY
> controlling signals of devices that might lead to human injury. Rather,
> such devices should be controlled by discrete hardware, perhaps as
> complex as an FPGA.

I'm not an expert, but I believe that the standards and requirements do 
not prohibit or mandate certain designs, but mandate certain analyses 
and the resulting assurances that the design has the required safety 
properties.

It is up to the designer to balance the complexity of the design against 
the complexity of the safety analysis or "safety case".

MISRA is more design-oriented.

> There is always going to be a chance that a real
> processor that, e.g., controls the enable signal to a laser is going to
> crash with the signal enabled.

Often the design provides a separate control system and a separate 
safety system that monitors the control system and prevents unsafe 
behaviour.

> Let me get even more specific: would it be acceptable to use a processor
> running linux in such an application? My gut reaction is "Not only no,
> but HELL no," but I'm not sure if I'm being overly cautious.

I don't thinkt that Linux would be prohibited out of hand, but showing 
that a Linux-based system has the required safety properties is probably 
harder than for a simpler, more to-the-point implementation.

HTH.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .

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Thread

Safety-Critical Software Design Randy Yates <yates@digitalsignallabs.com> - 2016-07-17 00:57 -0400
  Re: Safety-Critical Software Design Paul Rubin <no.email@nospam.invalid> - 2016-07-16 23:10 -0700
  Re: Safety-Critical Software Design Niklas Holsti <niklas.holsti@tidorum.invalid> - 2016-07-17 09:16 +0300
  Re: Safety-Critical Software Design Reinhardt Behm <rbehm@hushmail.com> - 2016-07-17 14:38 +0800
  Re: Safety-Critical Software Design upsidedown@downunder.com - 2016-07-17 10:37 +0300
  Re: Safety-Critical Software Design Don Y <blockedofcourse@foo.invalid> - 2016-07-17 03:09 -0700
    Re: Safety-Critical Software Design Don Y <blockedofcourse@foo.invalid> - 2016-07-17 03:32 -0700
      Re: Safety-Critical Software Design Niklas Holsti <niklas.holsti@tidorum.invalid> - 2016-07-17 22:49 +0300
      Re: Safety-Critical Software Design Les Cargill <lcargill99@comcast.com> - 2016-07-26 11:20 -0500
  Re: Safety-Critical Software Design Tim Wescott <tim@seemywebsite.com> - 2016-07-17 20:51 -0500
  Re: Safety-Critical Software Design FreeRTOS info <noemail@given.com> - 2016-07-21 10:33 +0100
  Re: Safety-Critical Software Design Les Cargill <lcargill99@comcast.com> - 2016-07-26 11:17 -0500

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