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Groups > comp.lang.c > #401310
| From | cross@spitfire.i.gajendra.net (Dan Cross) |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Microcontroller software stacks (was Re: this girl calls c ugly) |
| Date | 2026-08-18 20:32 +0000 |
| Organization | PANIX Public Access Internet and UNIX, NYC |
| Message-ID | <1162fgr$dv8$1@reader1.panix.com> (permalink) |
| References | <10v7b32$2u85v$1@dont-email.me> <86h5mv8umk.fsf@linuxsc.com> <111b3ni$s5m$1@reader1.panix.com> <861pc078pc.fsf@linuxsc.com> |
In article <861pc078pc.fsf@linuxsc.com>,
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>cross@spitfire.i.gajendra.net (Dan Cross) writes:
>
>> In article <86h5mv8umk.fsf@linuxsc.com>,
>> Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
>>
>>> 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?
>>
>> No. There are issues of alignment and padding one must consider
>> when using bitfields to model hardware registers, particularly
>> if (say) a device driver is meant to be shared across ISAs.
>>
>> Using the exact width types really does make a difference; it's
>> IB what those properties are, though we're usually at the mercy
>> of the target platform's ABI anyway at that point.
>
>The motivation for my query was not to ask an abstract theoretical
>question but a specific and pragmatic one.
My response was practical and pragmatic, and arises in code that
is written by real-world systems programmers.
I understand that is not your domain of expertise.
- 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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