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NAME
ads111x — driver for ADS101x and ADS111x i2c analog to digital converters
SYNOPSIS
To compile this driver into the kernel, place the following line in your kernel
configuration file:
device ads111x
Alternatively, to load the driver as a module at boot time, place the following line in
loader.conf(5):
ads111x_load="YES"
DESCRIPTION
The ads111x 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 sysctl(8).
Sysctl(8) provides access to the voltage measurements made by the device. Each time the
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.
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
ads111x 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.
For devices that include an alert output pin, the ads111x 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.
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 loader(8)
tunables. Channel numbers in these sysctl variables range from 0 through 7.
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.
dev.ads111x.<unit>.lo_thresh
Sets the low threshold for activating the alert pin.
dev.ads111x.<unit>.hi_thresh
Sets the high threshold for activating the alert pin.
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.
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.
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.
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.
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.
HARDWARE
The ads111x driver provides support for the following devices:
ADS1013 ADS1113
ADS1014 ADS1114
ADS1015 ADS1115
FDT CONFIGURATION
On an fdt(4) based system, the ads111x device is defined as a slave device subnode of the
i2c bus controller node. All properties documented in the ads1015.txt bindings document can
be used with the ads111x device.
The following properties are required in the ads111x device subnode:
compatible
One of the following:
“ti,ads1013 “ti,ads1113””
“ti,ads1014 “ti,ads1114””
“ti,ads1015 “ti,ads1115””
reg I2c slave address of device.
Specific channels can be configured by adding child nodes to the ads111x 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.
Example including channel configuration
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>;
};
};
HINTS CONFIGURATION
On a device.hints(5) based system, such as MIPS, these values are configurable for ads111x:
hint.ads111x.<unit>.at
The iicbus instance the ads111x instance is attached to.
hint.ads111x.<unit>.<channel>.gain_index
The amplifier gain, as described above for the sysctl variable
dev.ads111x.<unit>.<channel>.gain_index.
hint.ads111x.<unit>.<channel>.rate_index
The sample rate, as described above for the sysctl variable
dev.ads111x.<unit>.<channel>.rate_index.
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.
SEE ALSO
fdt(4), sysctl(8)
HISTORY
The ads111x driver first appeared in FreeBSD 13.0.