ads111x —
driver
for ADS101x and ADS111x i2c analog to digital converters
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):
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 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.
The
ads111x driver provides support for the
following devices:
| ADS1013 |
ADS1113 |
| ADS1014 |
ADS1114 |
| ADS1015 |
ADS1115 |
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.
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>;
};
};
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.
fdt(4),
sysctl(8)
The
ads111x driver first appeared in
FreeBSD 13.0.