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Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on

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On 10/25/21 2:15 PM, pozz wrote:
> Il 23/10/2021 18:09, David Brown ha scritto:
> [...]
>> Marking "in" and "buf" as volatile is /far/ better than using a critical
>> section, and likely to be more efficient than a memory barrier.  You can
>> also use volatileAccess rather than making buf volatile, and it is often
>> slightly more efficient to cache volatile variables in a local variable
>> while working with them.
> 
> I think I got your point, but I'm wondering why there are plenty of 
> examples of ring-buffer implementations that don't use volatile at all, 
> even if the author explicitly refers to interrupts and multithreading.
> 
> Just an example[1] by Quantum Leaps. It promises to be a *lock-free* (I 
> think thread-safe) ring-buffer implementation in the scenario of single 
> producer/single consumer (that is my scenario too).
> 
> In the source code there's no use of volatile. I could call 
> RingBuf_put() in my rx uart ISR and call RingBuf_get() in my mainloop code.
> 
>  From what I learned from you, this code usually works, but the standard 
> doesn't guarantee it will work with every old, current and future 
> compilers.
> 
> 
> 
> [1] https://github.com/QuantumLeaps/lock-free-ring-buffer

The issue with not using 'volatile' (or some similar memory barrier) is 
that without it, the implementation is allowed to delay the actual write 
of the results into the variable.

If optimization is limited to just within a single translation unit, you 
can force it to work by having the execution path leave the translation 
unit, but with whole program optimization, it is theoretically possible 
that the implementation sees that the thread of execution NEVER needs it 
to be spilled out of the registers to memory, so the ISR will never see 
the change.

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How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-23 00:07 +0200
  Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Clifford Heath <no.spam@please.net> - 2021-10-23 13:40 +1100
  Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-22 22:09 -0700
    Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-23 22:12 +0200
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-23 15:59 -0700
  Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-23 18:09 +0200
    Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-23 22:49 +0200
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-24 13:02 +0200
        Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-24 17:39 +0200
          Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-24 18:37 +0200
    Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-25 20:15 +0200
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-25 20:54 +0200
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Richard Damon <Richard@Damon-Family.org> - 2021-10-25 20:31 -0400
  Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Johann Klammer <klammerj@NOSPAM.a1.net> - 2021-10-24 12:39 +0200
    Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-24 14:14 +0300
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-24 12:54 -0700
        Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-24 23:27 +0300
          Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-24 14:08 -0700
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 00:50 +0300
              Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-24 15:47 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 02:32 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-24 18:34 -0700
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-25 09:41 +0200
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 10:56 +0300
              Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 01:19 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 11:52 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 02:50 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-25 13:49 +0200
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 15:16 +0300
          Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 11:09 +0300
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 01:28 -0700
              Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 12:06 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 02:35 -0700
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 16:04 +0300
              Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 18:34 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 10:43 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 20:53 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 11:02 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-25 19:52 +0200
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 11:10 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 21:33 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 22:09 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-10-25 22:53 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Dimiter_Popoff <dp@tgi-sci.com> - 2021-10-25 23:02 +0300
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-26 00:05 +0200
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on pozz <pozzugno@gmail.com> - 2021-10-25 23:46 +0200
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-25 20:58 +0200
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Clifford Heath <no.spam@please.net> - 2021-10-26 08:43 +1100
        Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on antispam@math.uni.wroc.pl - 2021-10-25 21:32 +0000
          Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-25 15:24 -0700
            Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on antispam@math.uni.wroc.pl - 2021-10-27 00:20 +0000
              Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-26 17:52 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on antispam@math.uni.wroc.pl - 2021-10-27 05:22 +0000
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-29 15:36 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on antispam@math.uni.wroc.pl - 2021-10-31 22:54 +0000
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-10-31 20:37 -0700
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on antispam@math.uni.wroc.pl - 2021-11-11 04:34 +0000
                Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on Don Y <blockedofcourse@foo.invalid> - 2021-11-19 16:21 -0700
      Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on David Brown <david.brown@hesbynett.no> - 2021-10-25 08:57 +0200

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