1.\" $NetBSD: cmos.4,v 1.3 2007/02/07 07:28:29 dyoung 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.\" 3. David Young's name may not be used to endorse or promote 17.\" products derived from this software without specific prior 18.\" written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY DAVID YOUNG ``AS IS'' AND ANY 21.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 22.\" THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 23.\" PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DAVID 24.\" YOUNG BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 25.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 26.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 28.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 29.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 31.\" POSSIBILITY OF SUCH DAMAGE. 32.\" 33.Dd February 5, 2007 34.Os 35.Dt CMOS 4 i386 36.Sh NAME 37.Nm cmos 38.Nd Read/write access to IBM PC/AT CMOS RAM 39.Sh SYNOPSIS 40.Cd pseudo-device cmos 41.Sh DESCRIPTION 42Use 43.Nm 44to read the real-time clock and ISA configuration data from an 45ISA-compatible CMOS RAM, and to write the ISA configuration data. 46.Pp 47A program reads between 0 and 48 bytes from the CMOS RAM, starting at 48byte 0 of the RAM, using a single call to 49.Xr read 2 . 50Likewise, a program writes between 0 and 48 bytes to the CMOS RAM, 51starting at byte 0 of the RAM, using a single call to 52.Xr write 2 . 53.Pp 54.Nm 55does not allow programs to overwrite the real-time clock data 56(bytes 0 through 9), the status registers (10 through 13), 57the diagnostic status or CMOS shutdown status (bytes 14 and 15), 58or the CMOS checksum (bytes 46 and 47). 59Writes to those bytes are ignored. 60.Pp 61On writes, 62.Nm 63recomputes the CMOS checksum and writes it to the CMOS RAM. 64.Sh EXAMPLES 65Display entire contents of CMOS RAM: 66.Bd -literal -offset indent 67# dd if=/dev/cmos bs=48 count=1 | od -t x1 680000000 37 00 09 00 22 00 06 13 04 80 26 02 50 80 00 00 690000020 00 51 f0 00 01 80 02 00 fc 0f 2f 00 00 00 00 00 700000040 00 80 81 f0 ff 00 00 00 00 00 00 00 00 00 05 ee 710000060 72.Ed 73.Pp 74Change boot order on Soekris net4521 to PXE ROM, Primary HDD, 75Secondary HDD: 76.Bd -literal -offset indent 77# dd if=/dev/cmos of=/tmp/cmos0 bs=48 count=1 781+0 records in 791+0 records out 8048 bytes transferred in 0.001 secs (48000 bytes/sec) 81# cp /tmp/cmos0 /tmp/cmos 82# printf '\exf0\ex80\ex81\exff' | dd bs=1 seek=33 conv=notrunc of=/tmp/cmos 834+0 records in 844+0 records out 854 bytes transferred in 0.001 secs (4000 bytes/sec) 86# dd if=/tmp/cmos of=/dev/cmos 870+1 records in 880+1 records out 8948 bytes transferred in 0.001 secs (48000 bytes/sec) 90.Ed 91.Sh ERRORS 92A program can read or write no more than 48 bytes to 93.Nm . 94.Xr read 2 / 95.Xr write 2 96will return 97.Er EINVAL 98if more than 48 bytes are read / written at once. 99.Sh AUTHORS 100The original 101.Nm 102driver was written by 103.An Takahiro Kambe Aq taca@back-street.net . 104.An David Young Aq dyoung@NetBSD.org 105modified the original and added it to 106.Nx . 107.\" .Sh BUGS 108