Date: Sat, 14 Dec 2002 03:33:40 -0800 From: Wes Peters <wes@softweyr.com> To: "M. Warner Losh" <imp@bsdimp.com> Cc: langd-freebsd-hackers@leo.org, freebsd-hackers@FreeBSD.ORG Subject: Re: more kernel programming style questions Message-ID: <3DFB1714.C98D3F75@softweyr.com> References: <20021213115507.GE84493@atrbg11.informatik.tu-muenchen.de> <20021213.182741.39658511.imp@bsdimp.com>
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"M. Warner Losh" wrote:
>
> You are better off defining a series of macros that do proper
> bus_space_readN/bus_space_writeN for each of the fields in the
> register set. This will ensure that your driver works unaltered on
> other architectures.
>
> Directly accessing memory mapped devices is a bad idea. While it
> works on i386, there are some platforms that have special alignment
> constraints that the underlying hardware doesn't always follow.
As an example, I/O devices on the SPARC architecture are almost always
placed in an "alternate address space" which means they have to be
accessed using different instructions (LDA/STA) than those that access
memory (LD/ST). Attempting memory I/O to devices on SPARC is doomed
to failure. It's a whole new (portable) world, folks...
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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