Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
OW_TEMP(4)		 BSD 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 accu-
     racy 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 accu-
     racy and repeatability than their absolute	accuracy.  This	makes them
     well suited for control loops that	strive for stability and become	possi-
     ble 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 con-
     versions 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.

BSD				 July 20, 2015				   BSD

NAME | SYNOPSIS | DESCRIPTION | HARDWARE | SYSCTL | SEE ALSO | LEGAL | HISTORY | AUTHORS | BUGS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=ow_temp&sektion=4&manpath=FreeBSD+12.0-RELEASE+and+Ports>

home | help