Re: Storage needed when there are bit-field members

From	David Brown <david.brown@hesbynett.no>
Newsgroups	comp.lang.c
Subject	Re: Storage needed when there are bit-field members
Date	2026-08-21 13:41 +0200
Organization	A noiseless patient Spider
Message-ID	<1169dgl$7usb$1@dont-email.me> (permalink)
References	(11 earlier) <111soae$1eq8$1@kst.eternal-september.org> <11650g9$19gjl$1@paganini.bofh.team> <1165ai6$314h2$2@kst.eternal-september.org> <1166fo6$3blln$1@dont-email.me> <20260821143125.000012cb@yahoo.com>

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On 21/08/2026 13:31, Michael S wrote:
> On Thu, 20 Aug 2026 11:00:54 +0200
> David Brown <david.brown@hesbynett.no> wrote:
> 
>> It certainly applies to some of the smaller and
>> cheaper ARM Cortex-M cores (M0, M1, M23 - perhaps more).
> 
> Are you sure about M1?
> If true, it is disappointing.

I haven't dug through the documentation, but gcc certainly thinks so - 
packed fields are accessed by byte rather than misaligned word accesses. 
  It is possible, of course, that gcc is pessimistic here, or that 
misaligned accesses are an optional feature for the core.

Since the M1 targets soft cores on programmable logic, and support for 
misaligned accesses takes extra logic (consuming space and possibly 
reducing maximum clock speed) for a feature that is rarely useful on 
embedded systems, it does not surprise me that the M1 does not support it.

> 
> I would not touch Cortex-M0 or M23 for many other reasons so can't
> be disappointed about them.

I have not used these cores either, but there is nothing inherently 
wrong with them - they are useful for small, cheap and low-power 
microcontrollers.  I am sure there are aspects of these cores where I 
would have preferred a different choice of which features are missing 
(compared to their larger brother cores), but I expect that would always 
be true.

> 
> OTOH, M1 is something that in theory I like.
> Never used it, because original licensing terms were absolute
> non-starter for sort of projects that we are specializing in (volumes
> rarely reaching 1000 units and never 10,000), but I am very likely to
> use it if we ever chose to work with Microsemi, on which licensing of
> M1 is much saner.
>

Thread

Re: Microcontroller software stacks (was Re: this girl calls c ugly) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-06-21 14:13 -0700
  Re: Microcontroller software stacks (was Re: this girl calls c ugly) David Brown <david.brown@hesbynett.no> - 2026-06-22 08:58 +0200
    Re: Microcontroller software stacks (was Re: this girl calls c ugly) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-22 03:35 -0700
      Re: Microcontroller software stacks (was Re: this girl calls c ugly) cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-22 10:50 +0000
      Re: Microcontroller software stacks (was Re: this girl calls c ugly) David Brown <david.brown@hesbynett.no> - 2026-06-22 12:59 +0200
      Storage needed when there are bit-field members Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-06-28 09:42 -0700
        Re: Storage needed when there are bit-field members Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-28 18:06 -0700
          Re: Storage needed when there are bit-field members Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-28 20:20 -0700
            Re: Storage needed when there are bit-field members Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-14 14:56 -0700
              Re: Storage needed when there are bit-field members scott@slp53.sl.home (Scott Lurndal) - 2026-08-14 22:30 +0000
                Re: Storage needed when there are bit-field members Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-15 16:10 -0700
                Re: Storage needed when there are bit-field members scott@slp53.sl.home (Scott Lurndal) - 2026-08-16 15:20 +0000
                Re: Storage needed when there are bit-field members Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-23 07:53 -0700
                Re: Storage needed when there are bit-field members David Brown <david.brown@hesbynett.no> - 2026-08-23 17:33 +0200
            Re: Storage needed when there are bit-field members antispam@fricas.org (Waldek Hebisch) - 2026-08-19 19:34 +0000
              Re: Storage needed when there are bit-field members Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-19 15:26 -0700
                Re: Storage needed when there are bit-field members David Brown <david.brown@hesbynett.no> - 2026-08-20 11:00 +0200
                Re: Storage needed when there are bit-field members Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-20 03:30 -0700
                Re: Storage needed when there are bit-field members David Brown <david.brown@hesbynett.no> - 2026-08-20 13:58 +0200
                Re: Storage needed when there are bit-field members Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-20 13:37 -0700
                Re: Storage needed when there are bit-field members Michael S <already5chosen@yahoo.com> - 2026-08-21 14:31 +0300
                Re: Storage needed when there are bit-field members David Brown <david.brown@hesbynett.no> - 2026-08-21 13:41 +0200
                Re: Storage needed when there are bit-field members scott@slp53.sl.home (Scott Lurndal) - 2026-08-21 15:41 +0000
                Re: Storage needed when there are bit-field members Michael S <already5chosen@yahoo.com> - 2026-08-21 14:58 +0300
                Re: Storage needed when there are bit-field members scott@slp53.sl.home (Scott Lurndal) - 2026-08-20 14:50 +0000
                Re: Storage needed when there are bit-field members "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-20 12:31 -0700
                Re: Storage needed when there are bit-field members antispam@fricas.org (Waldek Hebisch) - 2026-08-20 19:55 +0000
                Re: Storage needed when there are bit-field members David Brown <david.brown@hesbynett.no> - 2026-08-21 08:57 +0200
                Re: Storage needed when there are bit-field members scott@slp53.sl.home (Scott Lurndal) - 2026-08-21 14:59 +0000
                Re: Storage needed when there are bit-field members Michael S <already5chosen@yahoo.com> - 2026-08-20 22:15 +0300
          Re: Storage needed when there are bit-field members Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-14 14:19 -0700
  Re: Microcontroller software stacks (was Re: this girl calls c ugly) cross@spitfire.i.gajendra.net (Dan Cross) - 2026-06-22 10:45 +0000
    Re: Microcontroller software stacks (was Re: this girl calls c ugly) scott@slp53.sl.home (Scott Lurndal) - 2026-06-22 15:23 +0000
    Re: Microcontroller software stacks (was Re: this girl calls c ugly) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-14 13:23 -0700
      Re: Microcontroller software stacks (was Re: this girl calls c ugly) cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-18 20:32 +0000
  Re: Microcontroller software stacks (was Re: this girl calls c ugly) scott@slp53.sl.home (Scott Lurndal) - 2026-06-22 15:04 +0000
    Re: Microcontroller software stacks (was Re: this girl calls c ugly) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-06-22 13:02 -0700
    Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-14 12:51 -0700
      Re: Microcontroller software stacks Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-15 05:02 +0800
        Re: Microcontroller software stacks bart <bc@freeuk.com> - 2026-08-15 01:18 +0100
          Re: Microcontroller software stacks Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-16 13:52 +0800
      Re: Microcontroller software stacks Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-14 14:06 -0700
      Re: Microcontroller software stacks scott@slp53.sl.home (Scott Lurndal) - 2026-08-14 21:42 +0000
        Re: Microcontroller software stacks Michael S <already5chosen@yahoo.com> - 2026-08-15 22:13 +0300
          Re: Microcontroller software stacks scott@slp53.sl.home (Scott Lurndal) - 2026-08-15 19:39 +0000
            Re: Microcontroller software stacks Michael S <already5chosen@yahoo.com> - 2026-08-15 23:22 +0300
              Re: Microcontroller software stacks scott@slp53.sl.home (Scott Lurndal) - 2026-08-16 14:38 +0000
                Re: Microcontroller software stacks Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-08-16 16:11 -0700
                Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-23 07:56 -0700
                Re: Microcontroller software stacks David Brown <david.brown@hesbynett.no> - 2026-08-23 17:37 +0200
                Re: Microcontroller software stacks scott@slp53.sl.home (Scott Lurndal) - 2026-08-23 16:09 +0000
                Re: Microcontroller software stacks "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-08-23 19:42 -0700
                Re: Microcontroller software stacks scott@slp53.sl.home (Scott Lurndal) - 2026-08-23 16:08 +0000
        Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-15 16:16 -0700
          Re: Microcontroller software stacks cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-18 20:34 +0000
          Re: Microcontroller software stacks antispam@fricas.org (Waldek Hebisch) - 2026-08-19 19:57 +0000
            Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-23 10:54 -0700
              Re: Microcontroller software stacks antispam@fricas.org (Waldek Hebisch) - 2026-08-23 21:22 +0000
        Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-15 17:31 -0700
  Re: Microcontroller software stacks (was Re: this girl calls c ugly) Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-08-20 04:51 +0800

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