1.\" $NetBSD: cmos.4,v 1.7 2010/04/21 02:59:29 jruoho Exp $ 2.\" 3.\" Copyright (c) 2007 David Young. All rights reserved. 4.\" 5.\" This manual page was written by David Young. 6.\" 7.\" Redistribution and use in source and binary forms, with or 8.\" without modification, are permitted provided that the following 9.\" conditions are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above 13.\" copyright notice, this list of conditions and the following 14.\" disclaimer in the documentation and/or other materials 15.\" provided with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY DAVID YOUNG ``AS IS'' AND ANY 18.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 19.\" THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 20.\" PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DAVID 21.\" YOUNG BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 22.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 23.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 25.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 26.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd April 21, 2010 31.Dt CMOS 4 i386 32.Os 33.Sh NAME 34.Nm cmos 35.Nd Read/write access to IBM PC/AT CMOS RAM 36.Sh SYNOPSIS 37.Cd pseudo-device cmos 38.Sh DESCRIPTION 39The 40.Nm 41pseudo-device can be used to read the real-time clock and 42.Tn ISA 43configuration data from an ISA-compatible 44.Tn CMOS 45.Tn RAM , 46and to write the 47.Tn ISA 48configuration data. 49.Pp 50A program reads between 0 and 48 bytes from the 51.Tn CMOS 52.Tn RAM , starting at 53byte 0 of the 54.Tn RAM , 55using a single call to 56.Xr read 2 . 57Likewise, a program writes between 0 and 48 bytes to the CMOS RAM, 58starting at byte 0 of the RAM, using a single call to 59.Xr write 2 . 60.Pp 61.Nm 62does not allow programs to overwrite the real-time clock data 63(bytes 0 through 9), the status registers (10 through 13), 64the diagnostic status or 65.Tn CMOS 66shutdown status (bytes 14 and 15), 67or the 68.Tn CMOS 69checksum (bytes 46 and 47). 70Writes to those bytes are ignored. 71.Pp 72On writes, 73.Nm 74recomputes the 75.Tn CMOS 76checksum and writes it to the 77.Tn CMOS 78.Tn RAM . 79.Sh EXAMPLES 80Display entire contents of CMOS RAM: 81.Bd -literal -offset 2n 82# dd if=/dev/cmos bs=48 count=1 | od -t x1 830000000 37 00 09 00 22 00 06 13 04 80 26 02 50 80 00 00 840000020 00 51 f0 00 01 80 02 00 fc 0f 2f 00 00 00 00 00 850000040 00 80 81 f0 ff 00 00 00 00 00 00 00 00 00 05 ee 860000060 87.Ed 88.Pp 89Change boot order on Soekris net4521 to 90.Tn PXE 91.Tn ROM , 92Primary 93.Tn HDD , 94Secondary 95.Tn HDD : 96.Bd -literal -offset 2n 97# dd if=/dev/cmos of=/tmp/cmos0 bs=48 count=1 981+0 records in 991+0 records out 10048 bytes transferred in 0.001 secs (48000 bytes/sec) 101# cp /tmp/cmos0 /tmp/cmos 102# printf '\exf0\ex80\ex81\exff' | dd bs=1 seek=33 conv=notrunc of=/tmp/cmos 1034+0 records in 1044+0 records out 1054 bytes transferred in 0.001 secs (4000 bytes/sec) 106# dd if=/tmp/cmos of=/dev/cmos 1070+1 records in 1080+1 records out 10948 bytes transferred in 0.001 secs (48000 bytes/sec) 110.Ed 111.Sh ERRORS 112A program can read or write no more than 48 bytes to 113.Nm . 114Both 115.Xr read 2 116and 117.Xr write 2 118will return 119.Er EINVAL 120if more than 48 bytes are read or written at once. 121.Sh AUTHORS 122The original 123.Nm 124driver was written by 125.An Takahiro Kambe Aq taca@back-street.net . 126.An David Young Aq dyoung@NetBSD.org 127modified the original and added it to 128.Nx . 129.\" .Sh BUGS 130