1.\" 2.\" Copyright (c) 2015 M. Warner Losh 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. The name of the author may not be used to endorse or promote products 11.\" derived from this software without specific prior written permission. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd July 20, 2015 28.Dt OW_TEMP 4 29.Os 30.Sh NAME 31.Nm ow_temp 32.Nd Dallas Semiconductor 1-Wire Temperature sensor 33.Sh SYNOPSIS 34.Cd device ow_temp 35.Sh DESCRIPTION 36The 37.Nm 38module supports many of the 1-Wire temperature sensors. 39.Pp 40The sensor is read periodically and the results returned via a 41.Xr sysctl 3 42as described below. 43.Sh HARDWARE 44These temperature sensors are supported by the 45.Nm 46driver: 47.Bl -tag -width MAX31820 -compact 48.It DS1820 491-Wire Digital Thermometer 50.It DS18S20 51High-Precision 1-Wire Digital Thermometer 52.It DS18B20 53Programmable Resolution 1-Wire Digital Thermometer 54.It DS1822 55Econo 1-Wire Digital Thermometer 56.It DS1825 57Programmable Resolution 1-Wire Digital Thermometer with 4-bit ID 58.It MAX31820 591-Wire, Parasite-Power, Ambient Temperature Sensor 60.El 61.Pp 62The driver supports Family codes 0x10, 0x22, 0x28, and 0x3b. 63.Sh SYSCTL 64The 65.Nm 66driver reports data via 67.Xr sysctl 8 68entries in the device's node in the 69.Xr sysctl 8 70tree: 71.Bl -tag -width xxxxxxxxxx 72.It temperature 73The last temperature read, in milli-Kelvin. 74.It badcrc 75The number of CRC errors in reading the temperature form the 76device. 77Some CRC errors are to be expected. 78High rates of CRC errors, however, generally indicate a noisy 79environment, cabling issues, or too many devices on the bus. 80.It badread 81The number of times a non-CRC error was encountered reading the temperature 82from the card. 83This type of error is very rare. 84.It reading_interval 85The time, in ticks, between successive reads of the sensor. 86.It parasite 87This item is non-zero when the device is connected using its parasitic 88power mode. 89It can also indicate a wiring error. 90.El 91.Pp 92Temperatures are reported in milli-Kelvin, even though the absolute 93accuracy is around 0.2 degrees for the good devices and around 1 94degree for cheaper devices. 95The devices report in steps of 0.0625 degrees. 96The driver preserves the precision of the device's measurements 97in its 98.Xr sysctl 8 99reports. 100These devices often have a much higher relative accuracy and 101repeatability than their absolute accuracy. 102This makes them well suited for control loops that strive for 103stability and become possible if the full precision is preserved. 104.Sh SEE ALSO 105.Xr ow 4 , 106.Xr owc 4 , 107.Xr sysctl 8 , 108.Xr owll 9 , 109.Xr own 9 110.Sh LEGAL 111.Tn 1-Wire 112is a registered trademark of Maxim Integrated Products, Inc. 113.Sh HISTORY 114The 115.Nm 116driver first appeared in 117.Fx 11.0 . 118.Sh AUTHORS 119The 120.Nm 121device driver and this manual page were written by 122.An Warner Losh . 123.Sh BUGS 124The parasitic mode of the devices does not work. 125It requires support from the 126.Xr owc 4 127driver that is unimplemented. 128.Pp 129The ID bits from the 130.Em DS1825 131are not recognized or reported. 132.Pp 133The type of the device is not reported via 134.Xr sysctl 8 . 135.Pp 136Alarm mode is not supported. 137It is not possible to set the low and high alarm temperatures. 138.Pp 139There is no way to write to the EEPROM. 140.Pp 141.Dq Convert Temperature 142requests are sent directly to the device. 143There is no way to use the broadcast ability of the 1-Wire bus to do 144all the conversions in parallel. 145.Pp 146It is not possible to set the precision on those devices that support 147it. 148.Pp 149The time to convert is fixed at 1 second, even though some devices are 150faster. 151.Pp 152There is no character device to supply a stream of readings to a 153program. 154Programs interested in the temperature must poll the sysctl to get the 155temperature. 156