Re: [EE] Ideas about improving safety in C language

There is a subset of C, combined with extra rules about use and software
which checks to make sure the rules are being followed, which is called
MISRA C and is often used for life critical safety applications. It has a
pretty good record from what I understand. It is rather old now (it was
developed 30 years ago but has been updated several times and is still in
widespread use. They supposedly have a version for C++ but since C++ relies
on garbage collection and other background tasks I don't see how it really
can be "safe" unless you essentially reduce it to C with a few minor
enhancements.

I have written safety-critical FPGA logic in VHDL and had it pass the
requirements placed on it by auditors (after I made some changes they
requested). I was not required to use special synthesis software or
restrict the language constructs I used (other than the usual
recommendations and restrictions which are needed for synthesizability).
This was for a SIL 2 application so not like a nuclear power plant or
airplane autopilot. Just a safety system for industrial machines. On my own
I made almost every part of the logic check itself periodically and
lock-out if it failed the test. Many of the functions were redundant with
lock-out on comparison failure and some of them were 2 of 3 redundant (two
out of 3 have to fail to cause a dangerous fault). I also forced the
synthesis engine to put the safety part of the logic in one section of the
FPGA and constrained the IO from it to the rest of the logic to a minimum
number of signals and we did extensive testing at that interface level and
at each submodule.  We could then freely make changes to the bulk of the
logic without re-approval as long as we didn't touch the safety logic.
FPGA's lend themselves well to this kind of safety structure. With C code
compiled and running on processors, you often also need to run multiple
processors in lock-step and compare their outputs as well as run periodic
diagnostics. All of that is separate from MISRA standards.

Sean


On Tue, Apr 15, 2025 at 4:33 PM smplx <[email protected]> wrote:

>
>
> On Tue, 15 Apr 2025, Isaac Marino Bavaresco wrote:
>
> > Hi folks,
> >
> > I was thinking about the current discussion about C/C++ language safety,
> > and I recalled an old idea I had long ago about creating a new string
> > format and library.
> >
> > It could be possible for one person alone to implement and use it
> > privately, but of course it would be even better if it becomes a
> > standard, perhaps with support from the compilers.
> >
> > I don't know whether something similar was already suggested or is being
> > used, but I would like to know your opinion about it.
> >
>
>
>
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