man/man4/ads111x.4

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.Dd September 2, 2019
.Dt ADS111x 4
.Os
.Sh NAME
.Nm ads111x
.Nd driver for ADS101x and ADS111x i2c analog to digital converters
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ads111x"
.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
ads111x_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for the ADS101x/ADS111x family of analog
to digital converter (ADC) devices.
The supported devices are all similar to each other, varying in
features such as resolution and number of input channels.
The devices offer a number of configuration options which can be
set via hints, FDT data, and
.Xr sysctl 8 .
.Pp
The
.Xr sysctl 8
utility provides access to the voltage measurements made by the device.
Each time the
.Va dev.ads111x.<unit>.<channel>.voltage
variable is accessed for a given channel, the driver switches the
chip's internal mux to choose the right input pins for that channel,
directs it to make a single measurement, and returns the measured value
in microvolts.
The amount of time required to make the measurement is a function
of the sampling rate configured for the device.
While device is directed to make a single measurement, it still averages
the input values for the same amount of time as it would to emit one
sample if it were in continuous mode.
For example, if the sample rate were configured as 125 samples per
second, a single measurement would require 8 milliseconds.
.Pp
For devices that support multiple input pins, the device datasheet
describes mux settings to control how those pins are interpeted when
making either single-ended or differential measurements.
There are eight possible ways to combine the inputs from the four pins.
The
.Nm
driver models that by creating a separate output channel for each of
the eight combinations.
To make a measurement on a given pin or pair of pins, you simply access
the voltage variable for the channel number that corresponds the mux
setting number (0 through 7) shown in the datasheet.
When the driver is configured with hints or FDT data, it creates
sysctl variables for just the channels specified in the config data.
When there is no channel config data, it creates all eight possible
channels so that you can access whichever one(s) you need.
.Pp
For devices that include an
.Va alert
output pin, the
.Nm
driver does not directly support the pin in terms of sensing or
acting on changes in the pin state.
However, you may connect the pin to a gpio input or fan controller
or other external device, and use the driver's sysctl variables to
configure behavior and threshold values for the pin.
The driver avoids perturbing your settings as it does other
manipulations to the config register.
.Sh SYSCTL VARIABLES
Sysctl variables are used to access the voltage measurements, and to
change the configuration of the channels.
All writeable variables may also be set as
.Xr loader 8
tunables.
Channel numbers in these sysctl variables range from 0 through 7.
.Bl -tag -width indent
.It Va dev.ads111x.<unit>.config
Provides access to the configuration register bits that control the
alert pin configuration.
Other bits which are controlled by the driver are masked out, and
cannot be viewed or changed using this variable.
.It Va dev.ads111x.<unit>.lo_thresh
Sets the low threshold for activating the alert pin.
.It Va dev.ads111x.<unit>.hi_thresh
Sets the high threshold for activating the alert pin.
.It Va dev.ads111x.<unit>.<channel>.rate_index
Sets the sample rate for the channel.
The device datasheet documents eight available sample rates, chosen
by setting a value of 0 through 7 into the corresponding control
register bits.
This variable sets the value used for those bits when making a
measurement on the given channel.
.Pp
Because measurements are always made in single-shot mode, think of
this variable as controlling the averaging time for a single sample;
the time to make a measurement is 1 / samplerate.
.It Va dev.ads111x.<unit>.<channel>.gain_index
Sets the programmable gain amplifier for the channel on devices
which have an internal amplifier.
The device datasheet documents eight available gain values, chosen
by setting a value of 0 through 7 into the corresponding control
register bits.
This variable sets the value used for those bits when making a
measurement on the given channel.
.It Va dev.ads111x.<unit>.<channel>.voltage
Reading this variable causes the device to make a measurement on
the corresponding input pin(s) and return the voltage in microvolts.
.Pp
Note that this variable does not appear when you list multiple
sysctl variables -- you must access it specifically by name, because
accessing it triggers device I/O.
.El
.Sh HARDWARE
The
.Nm
driver provides support for the following devices:
.Pp
.Bl -column -compact -offset indent "XXXXXXXX" "XXXXXXXX"
.It ADS1013 Ta ADS1113
.It ADS1014 Ta ADS1114
.It ADS1015 Ta ADS1115
.El
.Sh FDT CONFIGURATION
On an
.Xr fdt 4
based system, the
.Nm
device is defined as a slave device subnode
of the i2c bus controller node.
All properties documented in the
.Va ads1015.txt
bindings document can be used with the
.Nm
device.
.Pp
The following properties are required in the
.Nm
device subnode:
.Bl -tag -width indent
.It Va compatible
One of the following:
.Bl -column -compact -offset indent ".Dq ti,ads1013" ".Dq ti,ads1113"
.It Dq ti,ads1013 Ta Dq ti,ads1113
.It Dq ti,ads1014 Ta Dq ti,ads1114
.It Dq ti,ads1015 Ta Dq ti,ads1115
.El
.It Va reg
I2c slave address of device.
.El
.Pp
Specific channels can be configured by adding child nodes to the
.Nm
node, as described in the standard ads1015.txt bindings document.
If no channels are configured, sysctl variables will be created
for all possible channels supported by the device type, otherwise
only the specified channels are created.
.Ss Example including channel configuration
.Bd -unfilled -offset indent
adc@48 {
    compatible = "ti,ads1115";
    reg = <0x48>;
    status = "okay";
    #address-cells = <1>;
    #size-cells = <0>;

    channel@6 {
        reg = <6>;
        ti,gain = <3>;
        ti,datarate = <4>;
    };
    channel@7 {
        reg = <7>;
        ti,gain = <1>;
        ti,datarate = <7>;
    };
};
.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.ads111x.<unit>.at
The iicbus instance the
.Nm
instance is attached to.
.It Va hint.ads111x.<unit>.<channel>.gain_index
The amplifier gain, as described above for the sysctl variable
.Va dev.ads111x.<unit>.<channel>.gain_index .
.It Va hint.ads111x.<unit>.<channel>.rate_index
The sample rate, as described above for the sysctl variable
.Va dev.ads111x.<unit>.<channel>.rate_index .
.El
.Pp
If no channels are configured, sysctl variables will be created
for all possible channels supported by the device type, otherwise
only the specified channels are created.
.Sh SEE ALSO
.Xr fdt 4 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 13.0 .