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Re: Microcontroller software stacks

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: Microcontroller software stacks
Date 2026-08-15 16:16 -0700
Organization A noiseless patient Spider
Message-ID <868q673rft.fsf@linuxsc.com> (permalink)
References (5 earlier) <fkCTR.17300$_BG8.7520@fx24.iad> <86h5mv8umk.fsf@linuxsc.com> <oac_R.3743$Zhg2.1242@fx12.iad> <865x1c7a63.fsf@linuxsc.com> <iZLfS.7962$oxY4.4420@fx09.iad>

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scott@slp53.sl.home (Scott Lurndal) writes:

> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> scott@slp53.sl.home (Scott Lurndal) writes:
>>
>>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>>
>>>> scott@slp53.sl.home (Scott Lurndal) writes:
>>>>
>>>>> One might also define data structures for control and status
>>>>> registers using bitfield structs.
>>>>
>>>> Yeah.  This kind of application (among others) I consider one of
>>>> the motivating forces behind bitfields.
>>>>
>>>> [Some whitespace trimming done in the excerpt below.]
>>>>
>>>>> e.g. for the SATA UAHC_GLB_OOBR register:
>>>>>
>>>>> union UAHC_GBL_OOBR {
>>>>>   uint32_t u;
>>>>>   struct UAHC_GBL_OOBR_s {
>>>>> #if __BYTE_ORDER == __BIG_ENDIAN
>>>>>     uint32_t we     :  1; /**< R/W/H - Write enable. */
>>>>>     uint32_t cwmin  :  7; /**< R/W/H - COMWAKE minimum value [...] */
>>>>>     uint32_t cwmax  :  8; /**< R/W/H - COMWAKE maximum value [...] */
>>>>>     uint32_t cimin  :  8; /**< R/W/H - COMINIT minimum value [...] */
>>>>>     uint32_t cimax  :  8; /**< R/W/H - COMINIT maximum value [...] */
>>>>> #else
>>>>>     uint32_t cimax  :  8;
>>>>>     uint32_t cimin  :  8;
>>>>>     uint32_t cwmax  :  8;
>>>>>     uint32_t cwmin  :  7;
>>>>>     uint32_t we     :  1;
>>>>> #endif
>>>>>   } s;
>>>>> };
>>>>
>>>> To me it seems kind of goofy to use uint32_t for the bitfields type.
>>>> I would just use unsigned, which is just as sure to work as intended,
>>>> isn't it?
>>>
>>> The SATA hardware register is defined as a 32-bit register in the
>>> SATA specification.  Therefore we explicitly declare it as such.
>>
>> I understand the motivation for using uint32_t for the union member
>> u.  My question is only about the type used for the bitfields.  Do
>> you know of any platform, or even suspect that there might be a
>> platform, where using 'unsigned' rather than 'uint32_t' for the type
>> of the bitfields makes any difference at all?
>
> I haven't canvassed all the available platforms, and don't have
> any desire so to do.  In my opinion, using the same type for the
> bitfield members as was used for the corresponding union
> element is simply logical.   If we declare the integer part
> of the union as uint64_t,  we use the same time for the
> bitfields (and yes, we could have used unsigned long
> (or unsigned long long on the micky OS) - uint64_t
> is less typing.

To me it seems more logical to use the smallest basic type that
suffices for the width of the associated bit-field, assuming
the compiler allows it, or 'unsigned' for compilers that don't
provide those extensions.

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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> - 2026-08-14 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> - 2026-08-15 16:16 -0700
          Re: Microcontroller software stacks cross@spitfire.i.gajendra.net (Dan Cross) - 2026-08-18 20:34 +0000
        Re: Microcontroller software stacks Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-08-15 17:31 -0700

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