1.\" $NetBSD: cmos.4,v 1.6 2009/10/19 23:19:38 rmind 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 February 5, 2007 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 39Use 40.Nm 41to read the real-time clock and ISA configuration data from an 42ISA-compatible CMOS RAM, and to write the ISA configuration data. 43.Pp 44A program reads between 0 and 48 bytes from the CMOS RAM, starting at 45byte 0 of the RAM, using a single call to 46.Xr read 2 . 47Likewise, a program writes between 0 and 48 bytes to the CMOS RAM, 48starting at byte 0 of the RAM, using a single call to 49.Xr write 2 . 50.Pp 51.Nm 52does not allow programs to overwrite the real-time clock data 53(bytes 0 through 9), the status registers (10 through 13), 54the diagnostic status or CMOS shutdown status (bytes 14 and 15), 55or the CMOS checksum (bytes 46 and 47). 56Writes to those bytes are ignored. 57.Pp 58On writes, 59.Nm 60recomputes the CMOS checksum and writes it to the CMOS RAM. 61.Sh EXAMPLES 62Display entire contents of CMOS RAM: 63.Bd -literal -offset indent 64# dd if=/dev/cmos bs=48 count=1 | od -t x1 650000000 37 00 09 00 22 00 06 13 04 80 26 02 50 80 00 00 660000020 00 51 f0 00 01 80 02 00 fc 0f 2f 00 00 00 00 00 670000040 00 80 81 f0 ff 00 00 00 00 00 00 00 00 00 05 ee 680000060 69.Ed 70.Pp 71Change boot order on Soekris net4521 to PXE ROM, Primary HDD, 72Secondary HDD: 73.Bd -literal -offset indent 74# dd if=/dev/cmos of=/tmp/cmos0 bs=48 count=1 751+0 records in 761+0 records out 7748 bytes transferred in 0.001 secs (48000 bytes/sec) 78# cp /tmp/cmos0 /tmp/cmos 79# printf '\exf0\ex80\ex81\exff' | dd bs=1 seek=33 conv=notrunc of=/tmp/cmos 804+0 records in 814+0 records out 824 bytes transferred in 0.001 secs (4000 bytes/sec) 83# dd if=/tmp/cmos of=/dev/cmos 840+1 records in 850+1 records out 8648 bytes transferred in 0.001 secs (48000 bytes/sec) 87.Ed 88.Sh ERRORS 89A program can read or write no more than 48 bytes to 90.Nm . 91.Xr read 2 92/ 93.Xr write 2 94will return 95.Er EINVAL 96if more than 48 bytes are read / written at once. 97.Sh AUTHORS 98The original 99.Nm 100driver was written by 101.An Takahiro Kambe Aq taca@back-street.net . 102.An David Young Aq dyoung@NetBSD.org 103modified the original and added it to 104.Nx . 105.\" .Sh BUGS 106