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4 .\" Copyright (c) 2019 Ian Lepore <ian@freebsd.org>
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34 .Nd driver for DHTxx and AM320x temperature and humidity sensors
36 To compile this driver into the kernel,
37 place the following line in your
38 kernel configuration file:
39 .Bd -ragged -offset indent
43 Alternatively, to load the driver as a
44 module at boot time, place the following line in
46 .Bd -literal -offset indent
52 driver supports the DHTxx and AM320x family of
53 temperature and humidity sensors.
54 The driver automatically reads the values from the sensor
55 once every 5 seconds, and makes the results available via
61 driver provides support for the following devices:
63 .Bl -column -compact -offset indent "XXXXXXXX" "XXXXXXXX"
69 The supported devices are all similar to each other, varying
70 primarily in accuracy and resolution.
71 The devices require a single wire for data communications, using a
72 custom protocol which is not compatible with Maxim's 1-wire(tm).
73 The AM320x devices also support connection to an i2c bus,
74 but this driver supports only the single-wire connection option.
76 Sysctl variables are used to access the most recent temperature and
77 humidity measurements.
78 .Bl -tag -width indent
79 .It Va dev.gpioths.<unit>.temp
80 The current temperature in integer deciKelvins.
83 will convert those units to display in decimal degrees Celcius.
84 .It Va dev.gpioths.<unit>.hum
85 The current relative humidity, as an integer percentage.
86 .It Va dev.gpioths.<unit>.fails
87 The number of failed attempts to communicate with the sensor since
89 Cleared whenever a set of measurements is successfully retrieved.
96 device node is typically defined directly under the root node, or under
97 a simplebus node that represents a collection of devices on a board.
99 The following properties are required in the
102 .Bl -tag -width indent
106 A reference to the gpio device and pin for data communications.
108 .Ss Example of adding a sensor with an overlay
109 .Bd -unfilled -offset indent
112 #include <dt-bindings/gpio/gpio.h>
115 compatible = "wand,imx6q-wandboard";
120 compatible = "dht11";
121 gpios = <&gpio5 15 GPIO_ACTIVE_HIGH>;
125 .Sh HINTS CONFIGURATION
128 based system, such as
130 these values are configurable for
132 .Bl -tag -width indent
133 .It Va hint.gpioths.<unit>.at
138 instance is attached to.
139 .It Va hint.gpioths.pins
140 A bitmask with a single bit set to indicate which gpio pin on the
142 to use for data communications.
151 driver first appeared in