Date: Thu, 17 Apr 1997 13:05:40 -0700 From: Julian Elischer <julian@whistle.com> To: Brett Glass <brett@lariat.org> Cc: dk+@ua.net, freebsd-hardware@FreeBSD.org Subject: Re: talk to I/O Devices. Message-ID: <33568294.2781E494@whistle.com> References: <3.0.1.32.19970417092103.0070f97c@lariat.org>
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Brett Glass wrote: > > At 11:54 PM 4/16/97 -0700, Dmitry Kohmanyuk wrote: > > >> Fascinating. What does opening this "file" actually do? (I can't find it > >> in the source.) > > > >look at /sys/i386/i386/mem.c:mmopen() and others in that file. > > Just looked at it, and it appears that this file opens the I/O space > as a random-access device. But accessing ports this way would slow > code down so dramatically that it could be useless for many > control applications! Also, the sample code in previous messages in > this thread seems to indicate that one can read and write directly. > How is this done? > > --Brett no, openning /dev/io doesn't do anything except set a bit on your process descriptor that allows your process to do IO instructions directly.. otherwise inb() and outb() are priveleged instructions and will cause an access fault.
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