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

Re:Lua-RTOS: a real-time operating system for ESP32 by caseymarquis on Wednesday June 09, 2021 @07:37AM (#27446728)

I think anything truly real time would be interrupt driven and use C/assembly. This would act as the glue between that critical code. I don't feel like we've hit peak embedded development yet. I love the idea of rapid embedded development that deploys scripts over a network or RS232, but most scripting languages aren't great for this. I would like to see a statically typed actor system with no GC or optional per actor GC that is pre-allocated and can only cause a single actor to fail in a predictable way.

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Re:Lua-RTOS: a real-time operating system for ESP32 by cinntaile on Wednesday June 09, 2021 @10:07AM (#27448000)

There are languages invented for this purpose, such as Ada. I'd look at that instead of C when you're doing real time systems. Although there are many different kinds of real time systems so it depends on the goal. Soft real time systems aren't as time critical as hard real time systems so the way you program and reason about them is a bit different.

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Re:Lua-RTOS: a real-time operating system for ESP32 by bluGill on Wednesday June 09, 2021 @08:12AM (#27446991)

How real time do you need to be? some real time is you need to react within milliseconds or bad things happen, humans will notice if there is 10ms lag in real time audio. Some real time is you need to react within seconds. A machine might need several tens of seconds to get up to speed, so controlling the motor only needs to update a once a second or so for the speed to remain within tolerance. And everything in between.

Depending on where you are on the need for control different technologies can work for you.

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Re:Lua-RTOS: a real-time operating system for ESP32 by detinho on Wednesday June 09, 2021 @09:04AM (#27447387)

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.

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Re:Lua-RTOS: a real-time operating system for ESP32 by tdeck on Wednesday June 09, 2021 @05:09PM (#27453260)

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

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Re:Lua-RTOS: a real-time operating system for ESP32 by bluGill on Wednesday June 09, 2021 @10:12AM (#27448056)

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.

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Re:Lua-RTOS: a real-time operating system for ESP32 by fullstop on Wednesday June 09, 2021 @09:09AM (#27447444)

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.

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Re:Lua-RTOS: a real-time operating system for ESP32 by monocasa on Wednesday June 09, 2021 @09:42AM (#27447725)

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.

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Re:Lua-RTOS: a real-time operating system for ESP32 by fullstop on Wednesday June 09, 2021 @10:16AM (#27448126)

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

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Re:Lua-RTOS: a real-time operating system for ESP32 by monocasa on Wednesday June 09, 2021 @10:26AM (#27448242)

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

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Re:Lua-RTOS: a real-time operating system for ESP32 by fullstop on Wednesday June 09, 2021 @10:30AM (#27448297)

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.

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Re:Lua-RTOS: a real-time operating system for ESP32 by monocasa on Wednesday June 09, 2021 @10:37AM (#27448387)

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".

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Re:Lua-RTOS: a real-time operating system for ESP32 by detinho on Wednesday June 09, 2021 @12:27PM (#27449838)

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.

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