OW_TEMP(4)             FreeBSD Kernel Interfaces Manual             OW_TEMP(4)

NAME
     ow_temp - Dallas Semiconductor 1-Wire Temperature sensor

SYNOPSIS
     device ow_temp

DESCRIPTION
     The ow_temp module supports many of the 1-Wire temperature sensors.

     The sensor is read periodically and the results returned via a sysctl(3)
     as described below.

HARDWARE
     These temperature sensors are supported by the ow_temp driver:
     DS1820    1-Wire Digital Thermometer
     DS18S20   High-Precision 1-Wire Digital Thermometer
     DS18B20   Programmable Resolution 1-Wire Digital Thermometer
     DS1822    Econo 1-Wire Digital Thermometer
     DS1825    Programmable Resolution 1-Wire Digital Thermometer with 4-bit
               ID
     MAX31820  1-Wire, Parasite-Power, Ambient Temperature Sensor

     The driver supports Family codes 0x10, 0x22, 0x28, and 0x3b.

SYSCTL
     The ow_temp driver reports data via sysctl(8) entries in the device's
     node in the sysctl(8) tree:

     temperature
                 The last temperature read, in milli-Kelvin.

     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.

     badread     The number of times a non-CRC error was encountered reading
                 the temperature from the card.  This type of error is very
                 rare.

     reading_interval
                 The time, in ticks, between successive reads of the sensor.

     parasite    This item is non-zero when the device is connected using its
                 parasitic power mode.  It can also indicate a wiring error.

     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
     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.

SEE ALSO
     ow(4), owc(4), sysctl(8), owll(9), own(9)

LEGAL
     1-Wire is a registered trademark of Maxim Integrated Products, Inc.

HISTORY
     The ow_temp driver first appeared in FreeBSD 11.0.

AUTHORS
     The ow_temp device driver and this manual page were written by Warner
     Losh.

BUGS
     The parasitic mode of the devices does not work.  It requires support
     from the owc(4) driver that is unimplemented.

     The ID bits from the DS1825 are not recognized or reported.

     The type of the device is not reported via sysctl(8).

     Alarm mode is not supported.  It is not possible to set the low and high
     alarm temperatures.

     There is no way to write to the EEPROM.

     "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.

     It is not possible to set the precision on those devices that support it.

     The time to convert is fixed at 1 second, even though some devices are
     faster.

     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.

FreeBSD 13.1-RELEASE-p6          July 20, 2015         FreeBSD 13.1-RELEASE-p6