ow_temp4

Usage

Overview

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

The ow_temp driver supports the following temperature sensors:

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 from 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.

Legal

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