Re: Task priorities in non strictly real-time systems

Subject	Re: Task priorities in non strictly real-time systems
Newsgroups	comp.arch.embedded
References	<qung9m$m79$1@dont-email.me>
From	Richard Damon <Richard@Damon-Family.org>
Message-ID	<r0TPF.92057$Cb2.6528@fx44.iad> (permalink)
Organization	Forte - www.forteinc.com
Date	2020-01-03 21:46 -0500

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On 1/3/20 8:41 AM, pozz wrote:
> I have always worked on non real-time systems, i.e. when the reaction of 
> the system to an event should occur in a reasonable time. For example, 
> when the user presses a button, a motor should start rotating. If the 
> motor starts after 100us or 100ms is not so important.
> 
> I never used RTOS, so the architecture of my firmware is based on 
> "superloop technique" (background tasks running in the loop and 
> interrupts).
> 
> while(1) {
>    task1();
>    task2();
>    ...
> }
> 
> All the tasks don't block, ever. As a rule of thumb, I accept a block 
> time of maximum 100us-1ms. When the task needs to block for a greater 
> amount, I try to implement it as a state-machine, avoiding blocking.
> 
> The ISRs are very lightweight: they only set/get some flags or push/pop 
> a byte to/from FIFO queues.
> With 32-bits MCUs (modern Cortex-M MCUs), I can change 32-bits variables 
> (mainly the ticks of the system) in ISRs without caring of 
> race-conditions that could occur on 8-bits MCUS when the background 
> tasks access the same variables.
> 
> In the past I used this architecture with success even in medium-complex 
> systems featuring Ethernet, lwip, mbedTLS, USB and touchscreen (emWin).
> 
> Sincerely I think this architecture is good enough for all non real-time 
> systems, so I don't understand why to use a RTOS in those cases.
> However I need to use a RTOS (FreeRTOS) for the next project, because it 
> is one of the requirement. It isn't a real-time system, but the RTOS is 
> required.
> 
> I think I can convert my architecture to RTOS by creating a task for 
> each of the function I call in the superloop and starting the OS 
> scheduler. However now the task function can't return, so I can write it 
> in the following way:
> 
> void task1_main(void) {
>    while(1) {
>      task1();
>    }
> }
> 
> task1() can be the *same* function of the superloop architecture.
> 
> I can assign each task the same priority: in this case, FreeRTOS will 
> use round-robin scheduling, giving all the tasks the same opportunity to 
> run.
> 
> Is it correct?

I would likely make the loop:

     while(1){
         task1();
         taskYield();
     }

so that after task1 finishes what it was doing, you automatically roll 
to the next task rather than looping task1 for a full tick period, then 
switching to task2(), and so on. If the tasks naturally block/yield 
within them, then that isn't as needed.

Also, at that point you can undo all of your state-machining that was 
just to return and then resume where you left off. Which may make the 
code clearer.

The one difficulty is that, as has been mentioned, when two (or more) 
tasks share data, you need to add the needed protections to the access 
as they can now be effectively simultaneous. (Not really if it is a 
single core processor, but you can switch from one task to another at 
virtually arbitrary points)

As others have said, you can perhaps start with a single task written as 
before, and as you find the reasons they wanted an RTOS, move just that 
part into a separate task, maybe at a higher priority level.

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Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-03 14:41 +0100
  Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-03 15:19 +0100
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:25 +0100
      Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:32 -0600
        Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-05 16:49 -0500
          Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:05 -0600
        Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-05 17:08 -0700
          Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:26 -0600
            Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-05 22:10 -0700
              Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-06 07:37 -0600
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 17:21 -0700
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 19:23 -0600
              Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-06 20:36 -0500
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 01:38 -0600
                Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 06:53 -0500
            Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 07:13 -0500
            Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-07 10:11 +0100
              Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 07:05 -0500
              Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 19:34 -0600
          Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-06 10:44 +0200
            Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 02:51 -0700
              Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-06 15:39 +0200
                Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 13:29 -0500
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 14:38 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 07:05 +0200
                Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-07 13:09 -0500
                Re: Task priorities in non strictly real-time systems Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-07 20:53 +0200
                Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-08 08:43 +1100
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-08 00:33 +0200
                Re: Task priorities in non strictly real-time systems Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-08 15:26 +0200
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-08 00:08 +0200
                Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-07 10:37 +0100
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 16:10 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 07:37 +0200
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-07 01:49 -0600
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:43 -0700
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 10:21 +0200
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:42 -0700
                Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-07 22:23 -0500
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-09 22:07 +0200
                Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-07 10:54 +0200
                Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-07 06:43 -0700
          Re: Task priorities in non strictly real-time systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-06 18:01 +0100
            Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-06 19:47 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:58 +0100
      Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-05 14:26 +1100
        Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-05 11:21 +0200
          Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 14:07 +0100
            Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-05 17:46 +0200
              Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 19:08 +0100
        Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 13:56 +0100
        Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:39 -0600
          Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-06 07:44 +1100
            Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 21:00 -0600
              Re: Task priorities in non strictly real-time systems Clifford Heath <no.spam@please.net> - 2020-01-06 14:50 +1100
                Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-06 07:12 -0600
      Re: Task priorities in non strictly real-time systems Paul Rubin <no.email@nospam.invalid> - 2020-01-04 22:34 -0800
        Re: Task priorities in non strictly real-time systems David Brown <david.brown@hesbynett.no> - 2020-01-05 14:12 +0100
          Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-05 18:00 +0200
        Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:44 -0600
      Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 14:52 -0500
      Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-06 15:05 -0500
        Re: Task priorities in non strictly real-time systems gtwrek@sonic.net (gtwrek) - 2020-01-06 22:41 +0000
        Re: Task priorities in non strictly real-time systems Don Y <blockedofcourse@foo.invalid> - 2020-01-06 19:50 -0700
          Re: Task priorities in non strictly real-time systems George Neuner <gneuner2@comcast.net> - 2020-01-07 13:26 -0500
  Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-03 16:28 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:37 +0100
      Re: Task priorities in non strictly real-time systems Les Cargill <lcargill99@comcast.com> - 2020-01-05 13:46 -0600
        Re: Task priorities in non strictly real-time systems Niklas Holsti <niklas.holsti@tidorum.invalid> - 2020-01-05 22:44 +0200
  Re: Task priorities in non strictly real-time systems Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-03 11:49 -0800
  Re: Task priorities in non strictly real-time systems upsidedown@downunder.com - 2020-01-03 22:51 +0200
    Re: Task priorities in non strictly real-time systems pozz <pozzugno@gmail.com> - 2020-01-05 01:48 +0100
  Re: Task priorities in non strictly real-time systems Joe Chisolm <jchisolm6@earthlink.net> - 2020-01-03 15:34 -0600
  Re: Task priorities in non strictly real-time systems Richard Damon <Richard@Damon-Family.org> - 2020-01-03 21:46 -0500

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