xref: /freebsd-src/share/man/man4/gpioths.4 (revision fa9896e082a1046ff4fbc75fcba4d18d1f2efc19)

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.\" Copyright (c) 2019 Ian Lepore <ian@freebsd.org>
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.Dd December 8, 2019
.Dt GPIOTHS 4
.Os
.Sh NAME
.Nm gpioths
.Nd driver for DHTxx and AM320x temperature and humidity sensors
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device gpioths"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
gpioths_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver supports the DHTxx and AM320x family of
temperature and humidity sensors.
The driver automatically reads the values from the sensor
once every 5 seconds, and makes the results available via
.Xr sysctl 8
variables.
.Sh HARDWARE
The
.Nm
driver provides support for the following devices:
.Pp
.Bl -column -compact -offset indent "XXXXXXXX" "XXXXXXXX"
.It DHT11  Ta DHT12
.It DHT21  Ta DHT22
.It AM3201 Ta AM3202
.El
.Pp
The supported devices are all similar to each other, varying
primarily in accuracy and resolution.
The devices require a single wire for data communications, using a
custom protocol which is not compatible with Maxim's 1-wire(tm).
The AM320x devices also support connection to an i2c bus,
but this driver supports only the single-wire connection option.
.Sh SYSCTL VARIABLES
Sysctl variables are used to access the most recent temperature and
humidity measurements.
.Bl -tag -width indent
.It Va dev.gpioths.<unit>.temperature
The current temperature in integer deciKelvins.
Note that
.Xr sysctl 8
will convert those units to display in decimal degrees Celsius.
.It Va dev.gpioths.<unit>.humidity
The current relative humidity, as an integer percentage.
.It Va dev.gpioths.<unit>.fails
The number of failed attempts to communicate with the sensor since
the last good access.
Cleared whenever a set of measurements is successfully retrieved.
.El
.Sh FDT CONFIGURATION
On an
.Xr fdt 4
based system, a
.Nm
device node is typically defined directly under the root node, or under
a simplebus node that represents a collection of devices on a board.
.Pp
The following properties are required in the
.Nm
device subnode:
.Bl -tag -width indent
.It Va compatible
Must be "dht11".
.It Va gpios
A reference to the gpio device and pin for data communications.
.El
.Ss Example of adding a sensor with an overlay
.Bd -unfilled -offset indent
/dts-v1/;
/plugin/;
#include <dt-bindings/gpio/gpio.h>

/ {
    compatible = "wand,imx6q-wandboard";
};

&{/} {
    dht0 {
        compatible = "dht11";
        gpios = <&gpio5 15 GPIO_ACTIVE_HIGH>;
    };
};
.Ed
.Sh HINTS CONFIGURATION
On a
.Xr device.hints 5
based system, such as
.Li MIPS ,
these values are configurable for
.Nm :
.Bl -tag -width indent
.It Va hint.gpioths.<unit>.at
The
.Xr gpiobus 4
instance the
.Nm
instance is attached to.
.It Va hint.gpioths.pins
A bitmask with a single bit set to indicate which gpio pin on the
.Xr gpiobus 4
to use for data communications.
.El
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr gpiobus 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 11.1 .