128 lines
4.0 KiB
Groff
128 lines
4.0 KiB
Groff
.\" Copyright (c) 1986, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mem.4 8.1 (Berkeley) 6/5/93
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.\"
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.Dd June 5, 1993
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.Dt MEM 4 tahoe
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.Os
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.Sh NAME
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.Nm mem ,
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.Nm kmem ,
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.Nm vmem
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.Nd main memory
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.Sh DESCRIPTION
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The special file
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.Nm /dev/mem
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is an interface to the physical memory of the computer.
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Byte offsets in this file are interpreted as physical memory addresses.
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Reading and writing this file is equivalent to reading and writing
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memory itself.
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Only offsets within the bounds of
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.Nm /dev/mem
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are allowed.
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.Pp
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Kernel virtual memory is accessed through the interface
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.Nm /dev/kmem
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in the same manner as
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.Nm /dev/mem .
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Only kernel virtual addresses that are currently mapped to memory are allowed.
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.Pp
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The file
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.Nm /dev/vmem
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allows access to the mapped portion of the
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.Tn VERSAbus
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.Tn I/O
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space. On the Tahoe the upper megabyte
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of the physical address space is accessible through
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this file (0xfff00000 through 0xffffffff).
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Accesses to the upper 64 kilobytes of
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the
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.Tn I/O
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space result in
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.Tn VERSAbus
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transfers with a
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16-bit address (the offset in this region) and a
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.Dq No non-privileged short Tn I/O
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.Tn VERSAbus
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address modifier.
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Accesses to the remainder of the mapped region,
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result in
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.Tn VERSAbus
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transfers with a 24-bit address
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and a ``non-privileged standard''
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.Tn VERSAbus
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address
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modifier. This region is actually part of the region
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between 0xfeff0000 and 0xffff0000
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which generates
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.Tn VERSAbus
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transfers with a 24-bit address.
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Accesses to the remainder of the one gigabyte
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.Tn I/O
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space
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generate transfers that utilize a 32-bit address with
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a ``non-privileged extended'' address modifier. Any
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32-bit address generated by a cpu access to this part
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of the
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.Tn I/O
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space have the upper two bits zero; thus,
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for example, an access to physical address 0xfe000000
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causes the address 0x3e000000 to be supplied in the
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resultant
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.Tn VERSAbus
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read/write cycle.
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.Pp
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On the Tahoe, the
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base address for the
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per-process data of the current process
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is virtual address 0xbffff000.
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.Sh FILES
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.Bl -tag -width Pa -compact
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.It Pa /dev/mem
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.It Pa /dev/kmem
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.It Pa /dev/vmm
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.El
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.Sh HISTORY
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The
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.Nm mem ,
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.Nm kmem
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files appeared in
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.At v6 .
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The file
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.Nm vmem
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appeared in
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.Bx 4.3 tahoe .
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.Sh BUGS
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Memory files are accessed one byte
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at a time, an inappropiate method for some
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device registers.
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