Re: "Non-volatile" OS ?

"David R Brooks" <davebXXX@xxxxxxxxxxxx> wrote in message
news:5s9vg1hfn632quuc2ijf1kj63ifpul3pgg@xxxxxxxxxx
>I built such a system many years ago, on a smaller scale: Z80 with
> 64kB. Running a proprietary OS, similar to CP/M.
>
> The key was to define two additional device driver functions:
> "emergency stop" & "resume".

Similarly, I've used a warm-start system that looks like:
- on failing power, save context, and shut-down cleanly
- on start-up and stable power, re-initialise hardware, then restore
context if possible (validated etc); else do hard restart

Which seems to be what the OP wants. The difficulty is in defining
"context", and validating that context at power-up.

With a dedicated product, it's easy enough - decide which parameters/states
are expensive to restart, and store these at power-down in non-vol memory.
Do some sanity-checks at power-up, and you're done.

With a general-purpose RTOS, if you're trying to keep the RTOS task states
during power-down, it's a different ballgame, and I'm not convinced it's
either desirable or necessary as a general OS feature - the *actual*
physical context may be entirely different when the system wakes up,
seconds, hours, years later. Hardware will need re-initing anyway. Seems to
me better to store "hints" as to initial context, than to depend on an OS to
(effectively) pick up after an indefinite pause in a now-different hardware
environment with no insight into what's changed.

YMMV.

Steve
http://www.fivetrees.com


.

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