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Groups > comp.lang.c > #401311
| From | cross@spitfire.i.gajendra.net (Dan Cross) |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Microcontroller software stacks |
| Date | 2026-08-18 20:34 +0000 |
| Organization | PANIX Public Access Internet and UNIX, NYC |
| Message-ID | <1162fle$3a9$1@reader1.panix.com> (permalink) |
| References | <10v7b32$2u85v$1@dont-email.me> <865x1c7a63.fsf@linuxsc.com> <iZLfS.7962$oxY4.4420@fx09.iad> <868q673rft.fsf@linuxsc.com> |
In article <868q673rft.fsf@linuxsc.com>,
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>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.
You do not appear to actually write software that interfaces
directly with hardware in the manner that Scott and I (among
others) do.
- Dan C.
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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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