OW_TEMP(4)

✨ ow_temp(4) — the 1-Wire temperature sensor girlies ✨

okay so this is ow_temp(4), straight outta the Kernel Interfaces Manual, and she is the manual page for the Dallas Semiconductor 1-Wire Temperature sensor. buckle up bestie, we're reading temps 💖

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🌡️ NAME 🌡️

ow_temp — Dallas Semiconductor 1-Wire Temperature sensor

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✨ SYNOPSIS ✨

device ow_temp

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💅 DESCRIPTION 💅

The ow_temp module supports many of the 1-Wire temperature sensors. no cap, it's versatile like that 🦋

The sensor is read periodically and the results come back to you via a sysctl(3) — all the deets are down below 👇

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🎀 HARDWARE 🎀

These temperature sensors are supported by the ow_temp driver, and honestly? iconic lineup:

• 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. periodt 💅

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📊 SYSCTL 📊

The ow_temp driver reports data via sysctl(8) entries in the device's node in the sysctl(8) tree. here's the whole menu, no gatekeeping 🫶

• temperature — the last temperature read, in milli-Kelvin. that's the vibe check result right there 🔥
• badcrc — the number of CRC errors in reading the temperature from the device. ngl, some CRC errors are to be expected — she's just a little glitchy sometimes 😭. High rates of CRC errors, however, generally indicate a noisy environment, cabling issues, or too many devices on the bus. so if it's screaming, check your setup bestie 💀
• badread — the number of times a non-CRC error was encountered reading the temperature from the card. this type of error is very rare — like, main character of a rarity ✨
• reading_interval — the time, in ticks, between successive reads of the sensor. the gap between her little check-ins 🕐
• parasite — this item is non-zero when the device is connected using its parasitic power mode. it can also indicate a wiring error. so… not always what it looks like 👀

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 — which makes them so well suited for control loops that strive for stability, and that becomes possible if the full precision is preserved. ate and left no crumbs 🍓

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👀 SEE ALSO 👀

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

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⚖️ LEGAL ⚖️

1-Wire is a registered trademark of Maxim Integrated Products, Inc. gotta give credit where it's due bestie 💜

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📜 HISTORY 📜

The ow_temp driver first appeared in FreeBSD 11.0. she's been here a minute, and she's thriving 🌸

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👑 AUTHORS 👑

The ow_temp device driver and this manual page were written by Warner Losh. thank you for your service king 🫶✨

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💀 BUGS 💀

okay so this is the part where we keep it real. there are some things she cannot do, and pretending otherwise would be lying to you:

• The parasitic mode of the devices does not work. It requires support from the owc(4) driver that is unimplemented. so yeah, that one's just not happening 😭
• The ID bits from the DS1825 are not recognized or reported. the 4-bit ID is giving mysterious, unread ✨
• 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. no alarm girlies here 🙈
• 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. so no parallel slay, one at a time bestie 💅
• 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. she's on her own schedule 🕐
• 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. no push notifications, you gotta go ask her yourself 📲

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and that's the whole page babes 💖 this one came to you from Debian, dated July 20, 2015 — vintage but still serving. stay cozy, keep your bus quiet, and don't forget to poll 🎀✨💜