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

From	Dimiter_Popoff <dp@tgi-sci.com>
Newsgroups	comp.arch.embedded
Subject	Re: How to write a simple driver in bare metal systems: volatile, memory barrier, critical sections and so on
Date	2021-10-25 22:09 +0300
Organization	TGI
Message-ID	<sl6vcu$cca$1@dont-email.me> (permalink)
References	(5 earlier) <itn713FpntqU1@mid.individual.net> <sl6a1d$4ci$1@dont-email.me> <ito14pF55oU1@mid.individual.net> <sl6qtm$9oh$1@dont-email.me> <itobkaF258sU1@mid.individual.net>

Show all headers | View raw

On 10/25/2021 21:33, Niklas Holsti wrote:
> ....
> 
> If the FIFO implementation is based on just two pointers (read and 
> write), and each pointer is modified by just one of the two threads 
> (main thread = reader, and interrupt handler = writer), and those 
> modifications are both "volatile" AND atomic (which has not been 
> discussed so far, IIRC...), then one can do without a critical region. 
> But then detection of a full buffer needs one "wasted" element in the 
> buffer.

Why atomic? No need for that unless more than one interrupted task would
want to read from the fifo at the same time, which is nonsense. [I once
wasted a day looking at a garbled input from an auxiliary HV to a netMCA
only to discover I had left a shell to start via the same UART during
boot, through an outdated (but available) driver accessing the same
UART the standard driver through which the HV was used....
This across half the planet, customer was in South Africa. Not
an experience anybody would ask for, I can tell you :)].
Just like there is no need to mask interrupts, as you mentioned I
had said before.

> To avoid the wasted element, one could add a "full"/"not full" Boolean 
> flag. But that flag would be modified by both threads, and should be 
> modified atomically together with the pointer modifications, which (I 
> think) means that a critical section is needed.

Now this is where atomic access is necessary - for no good reason in
this case, as mentioned before, but if one wants to bang their head
in the wall this is the proper way to do it.
As for "volatile" I can't say much, but if this is the way to make
the compiler access every time the address declared such instead of
using some stale data it has then it would be needed of
course.

Thread

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

csiph-web