Re: Engineering degree for embedded systems

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.arch.embedded
Subject	Re: Engineering degree for embedded systems
Date	2017-08-08 10:23 +0200
Organization	A noiseless patient Spider
Message-ID	<ombs5g$iva$1@dont-email.me> (permalink)
References	(5 earlier) <ih%fB.549283$ji4.33992@fx10.am4> <Dp-dnb-kqe3Kph7EnZ2dnUU7-cPNnZ2d@supernews.com> <bpBhB.643592$ji4.555780@fx10.am4> <708a5706-d12f-6e8f-442d-44efeafb7cc9@electrooptical.net> <5C1iB.390268$gM6.248510@fx03.am4>

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On 07/08/17 19:40, Tom Gardner wrote:
> On 07/08/17 17:36, Phil Hobbs wrote:

>> My stuff is all pthreads, because std::thread didn't exist at the time,
>> but it does now, so presumably Boehm's input has been taken into account.
> 
> I'm told C/C++12 /finally/ has a memory model, so perhaps
> that will (a few decades too late) ameliorate the problem.
> We'll see, but I'm not holding my breath.

You mean C11/C++11 ?  There are, I believe, very minor differences
between the memory models of C11 and C++11, but they are basically the
same.  And they provide the required synchronisation and barrier
mechanisms in a standard form.  Whether people will use them
appropriately or not, is another matter.  In the embedded world there
seems to be a fair proportion of people that still think C89 is a fine
standard to use.  Standard atomics and fences in embedded C basically
means gcc 4.9 or newer, when C11 support was complete.  For C++ it was a
little earlier.  I don't know what other C or C++ compilers for embedded
use have C11/C++11 support, but gcc is the main one, especially for
modern standards support.  GNU ARM Embedded had 4.9 at the end of 2014,
but it takes time for manufacturer-supplied toolchains to update.

So yes, C11/C++11 solves the problem in a standardised way - but it will
certainly take time before updated tools are in common use, and before
people make use of the new features.  I suspect this will happen mainly
in the C++ world, where C++11 is a very significant change from older
C++ and it can make sense to move to C++11 almost as a new language.
Even then, I expect most people will either rely on their OS primitives
to handle barriers and fences, or use simple full barriers:

C11:
	atomic_thread_fence(memory_order_seq_cst);

C++11:
	std::atomic_thread_fence(std::memory_order_seq_cst);

replacing

gcc Cortex-M:
	asm volatile("dmb" : : : "memory");

Linux:
	mb()

The tools have all existed, even though C and C++ did not have memory
models before C11/C++11.  cpus, OS's, and compilers all had memory
models, even though they might not have been explicitly documented.

And people got some things right, and some things wrong, at that time.
I think the same thing will apply now that they /have/ memory models.

Thread

Engineering degree for embedded systems "hogwarts" <122707@EmbeddedRelated> - 2017-07-27 07:35 -0500
  Re: Engineering degree for embedded systems Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2017-07-27 15:25 +0200
    Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-07-30 12:05 -0400
      Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-07-30 19:05 +0100
        Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-01 08:55 -0400
          Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-01 14:23 +0100
            Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-03 11:03 -0400
              Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 10:35 +0100
                Re: Engineering degree for embedded systems John Devereux <john@devereux.me.uk> - 2017-08-06 14:40 +0100
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 12:51 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 20:13 +0100
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 19:21 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:40 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 15:18 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 15:27 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 16:47 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 17:30 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 18:35 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 18:56 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 19:02 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 19:08 -0400
                Re: Engineering degree for embedded systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-08-08 01:30 +0200
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 19:32 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 19:53 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 20:02 -0400
                Re: Engineering degree for embedded systems stephen@mpeforth.com (Stephen Pelc) - 2017-08-07 23:49 +0000
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 20:07 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 08:00 +0100
                Re: Engineering degree for embedded systems George Neuner <gneuner2@comcast.net> - 2017-08-07 01:21 -0400
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 17:15 +0300
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 20:21 +0100
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-07 10:35 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-07 12:54 +0200
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-07 12:34 +0200
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:43 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 12:50 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:36 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-07 18:40 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 10:23 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 09:46 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 11:26 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 11:09 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 12:56 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 15:56 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 17:11 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 16:33 +0100
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-08 21:07 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-09 10:03 +0200
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-10 14:30 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-10 15:11 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-16 18:39 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-17 09:37 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-17 08:24 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-17 16:06 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-17 12:15 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-18 14:45 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-25 09:51 -0400
          Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-01 20:46 -0500
            Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-02 09:30 +0200
              Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-05 15:11 -0500
              Re: Engineering degree for embedded systems Paul Rubin <no.email@nospam.invalid> - 2017-08-08 00:22 -0700
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 08:36 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 12:37 +0200
  Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-07-27 17:46 +0100
    Re: Engineering degree for embedded systems Grant Edwards <invalid@invalid.invalid> - 2017-07-27 16:54 +0000
      Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-07-27 19:57 +0100
  Re: Engineering degree for embedded systems Frank Miles <fpm@u.washington.edu> - 2017-07-27 16:58 +0000
    Re: Engineering degree for embedded systems Theo Markettos <theom+news@chiark.greenend.org.uk> - 2017-07-28 00:43 +0100
    Re: Engineering degree for embedded systems jim.brakefield@ieee.org - 2017-07-30 15:26 -0700
  Re: Engineering degree for embedded systems Chris <xxx.syseng.yyy@gfsys.co.uk> - 2017-07-27 23:45 +0000
  Re: Engineering degree for embedded systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-08-03 19:50 +0200
    Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-05 15:20 -0500
      Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 09:17 +0300
        Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-06 10:12 +0100
          Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 13:19 +0300
          Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-06 09:59 -0500
            Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-06 18:06 +0100
              Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 21:31 -0400
                Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-07 09:32 +0100
        Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-06 09:53 -0500
          Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-07 10:59 +0300
            Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-07 20:09 -0500
              Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-08 21:31 +0300
        Re: Engineering degree for embedded systems Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2017-08-21 11:28 +0200

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