.\" .\" Copyright (c) 2015 M. Warner Losh .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd July 20, 2015 .Dt OW_TEMP 4 .Os .Sh NAME .Nm ow_temp .Nd Dallas Semiconductor 1-Wire Temperature sensor .Sh SYNOPSIS .Cd device ow_temp .Sh DESCRIPTION The .Nm module supports many of the 1-Wire temperature sensors. .Pp The sensor is read periodically and the results returned via a .Xr sysctl 3 as described below. .Sh HARDWARE These temperature sensors are supported by the .Nm driver: .Bl -tag -width MAX31820 -compact .It DS1820 1-Wire Digital Thermometer .It DS18S20 High-Precision 1-Wire Digital Thermometer .It DS18B20 Programmable Resolution 1-Wire Digital Thermometer .It DS1822 Econo 1-Wire Digital Thermometer .It DS1825 Programmable Resolution 1-Wire Digital Thermometer with 4-bit ID .It MAX31820 1-Wire, Parasite-Power, Ambient Temperature Sensor .El .Pp The driver supports Family codes 0x10, 0x22, 0x28, and 0x3b. .Sh SYSCTL The .Nm driver reports data via .Xr sysctl 8 entries in the device's node in the .Xr sysctl 8 tree: .Bl -tag -width xxxxxxxxxx .It temperature The last temperature read, in milli-Kelvin. .It badcrc The number of CRC errors in reading the temperature form the device. Some CRC errors are to be expected. High rates of CRC errors, however, generally indicate a noisy environment, cabling issues, or too many devices on the bus. .It badread The number of times a non-CRC error was encountered reading the temperature from the card. This type of error is very rare. .It reading_interval The time, in ticks, between successive reads of the sensor. .It parasite This item is non-zero when the device is connected using its parasitic power mode. It can also indicate a wiring error. .El .Pp Temperatures are reported in milli-Kelvin, even though the absolute accuracy is around 0.2 degrees for the good devices and around 1 degree for cheaper devices. The devices report in steps of 0.0625 degrees. The driver preserves the precision of the device's measurements in its .Xr sysctl 8 reports. These devices often have a much higher relative accuracy and repeatability than their absolute accuracy. This makes them well suited for control loops that strive for stability and become possible if the full precision is preserved. .Sh SEE ALSO .Xr ow 4 , .Xr owc 4 , .Xr sysctl 8 , .Xr owll 9 , .Xr own 9 .Sh LEGAL .Tn 1-Wire is a registered trademark of Maxim Integrated Products, Inc. .Sh HISTORY The .Nm driver first appeared in .Fx 11.0 . .Sh AUTHORS The .Nm device driver and this manual page were written by .An Warner Losh . .Sh BUGS The parasitic mode of the devices does not work. It requires support from the .Xr owc 4 driver that is unimplemented. .Pp The ID bits from the .Em DS1825 are not recognized or reported. .Pp The type of the device is not reported via .Xr sysctl 8 . .Pp Alarm mode is not supported. It is not possible to set the low and high alarm temperatures. .Pp There is no way to write to the EEPROM. .Pp .Dq Convert Temperature requests are sent directly to the device. There is no way to use the broadcast ability of the 1-Wire bus to do all the conversions in parallel. .Pp It is not possible to set the precision on those devices that support it. .Pp The time to convert is fixed at 1 second, even though some devices are faster. .Pp There is no character device to supply a stream of readings to a program. Programs interested in the temperature must poll the sysctl to get the temperature.