Date: Sat, 13 Mar 1999 15:55:06 -0700 From: Wes Peters <wes@softweyr.com> To: Dennis <dennis@etinc.com> Cc: hackers@FreeBSD.ORG Subject: Re: 'C' language question Message-ID: <36EAECCA.42F5C549@softweyr.com> References: <199903132232.RAA19255@etinc.com>
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Dennis wrote:
>
> I have a memory mapped controller that requires that all of its
> register reads and writes be 32 bits....the follow code:
>
> *reg |= 0x80000000;
>
> generates a byte OR (ORB instruction) which trashes the register with
> gcc 2.9.2....a stupid "optimization" that happens to be wrong in this
> case.
>
> is there a declaration that will force the compiler to generate a 32bit
> OR (ORL instruction) on this?
No. Read the register into a word in memory (or a register in asm code),
set/clear bits in the word, then write the word back.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
http://www.softweyr.com/~softweyr wes@softweyr.com
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