On: Lua-RTOS: a real-time operating system for ESP32

[detinho]

I'm probably wrong, but isn't real time not about how fast you can react but if you can react on a defined time constraint? Or is there a time threshold you can't consider real time any more like 1 day? Edit: just like you said, 10ms, 1s, etc.

[tdeck → detinho]

You're correct, the definition requires that operations be bounded, not necessarily "fast".

[bluGill → detinho]

The time depends on your problem. The real time is more about bad things happen if you don't respond on time. If you click on a webpage and your browser times out loading it is a real time failure, but the failure isn't bad enough that anyone thinks of browsers as real time because the failure isn't really harmful.

[fullstop → detinho]

Maximum tick time for RTOS are usually measured in tenths of seconds. The range is typically from microseconds to about 100ms.

edit: updated to reflect that I meant "upper bound"

edit2: completely reworded to be more clear.

[monocasa → fullstop]

Time constraints on an RTOS are what you need them to be for the domain.

On the RTOS I was the lead for, some constraints were measured in 100s of ns.

Edit to address the edit: our upper bound in that case was single digit microseconds.

[fullstop → monocasa]

My point was that once you pass the 100ms mark most would not consider it "real-time".

[monocasa → fullstop]

Ah it reads backwards, that you're asserting no one actually deals with constraints tighter than 100 ms.

[fullstop → monocasa]

We're coming from different directions. My upper bound was "after this point it won't be rtos", but I've reworded it entirely to be more clear.

[monocasa → fullstop]

Upper bound is a specific term in real time also unfortunately.

Might I suggest wording such as "upper bound constraints exceeding 100ms aren't typically addressed with real time methods".

[detinho → monocasa]

For what I see from the discution it seems to be more a practical decision to not use real time resources and techniques for much higher times. So 1 day for example would be a waste of development time to try to use real time, you could use alerts and background jobs to fix issues. But when you reach shorter and shorter timeframes and bad things can happen a real time approach starts to make more sense.

Now, some parent comment mentioned RTOS. Maybe for a real time OS there would be a practical hard upper bound. But for real time systems in general this upper bound would be totally domain specific.