This version (21 Nov 2023 14:58) was approved by Marcelo Schmitt.

AD7091R-2/-4/-8 ADC Linux Driver

Supported Devices

Evaluation Boards

EVAL-AD7091R-2

Status

Source	Mainlined?
git	[Not yet]

Files

Function	File
header	master/drivers/iio/adc/ad7091r-base.h
base driver	master/drivers/iio/adc/ad7091r-base.c
chip driver	master/drivers/iio/adc/ad7091r8.c
devicetree bindings	Documentation/devicetree/bindings/iio/adc/adi,ad7091r8.yaml

Overview

The ad7091r-2, ad7091r-4, and AD7091r-8 are 2-/4-/8-channel, ultra lowpower power dissipation, 1 MSPS successive approximation register (SAR) analog-to-digital converter (ADC). The AD7091R-2/-4/-8 ADCs are multichannel versions of AD7091r. The AD7091R-2/AD7091R-4/AD7091R-8 operates from a single 2.7 V to 5.25 V power supply and is capable of achieving a sampling rate of 1 MSPS.

The AD7091R-2/AD7091R-4/AD7091R-8 family offers up to eight single-ended analog input channels with a channel sequencer that allows a preprogrammed selection of channels to be converted sequentially. Program the channel sequencer by writing to the channel register (address 0x01) through direct register access. AD7091R-2/-4/-8 devices can be fully configured by writing to the desired device registers through direct register access.

The conversion process and data acquisition are controlled using the CONVST pin, which is pulsed on every read to the conversion result register. Writing and reading to registers other than the conversion result register will not trigger a pulse on the CONVST line.

Hardware configuration

Use the test points for interfacing the EVAL-AD7091R-xSDZ with a machine running Linux.

The instructions below describe how to set up EVAL-AD7091R-xSDZ with RPI-4.

The evaluation board default configuration is intended to work with EVAL-SDP-CB1Z so it must be adapted to connect to a different platform.

For the jumper links, use the following configuration:

Link	Link Position
LK1	B
LK2	B
LK3	B
LK8	A
LK9	B
LK11	A

Use a soldering iron to change a few soldering links.

Unsolder R126 (enable drive CS through CS test point)
Unsolder R127 (enable drive SDI through SDI test point)
Unsolder R128 (enable drive CONVST through CONVST test point)
Unsolder SL19 (enable drive SCLK through SCLK test point)
Unsolder SL20 (enable drive SDO through SDO test point)
Power VDD and Vdrive supplied with RPI-4 3.3V pins.
Solder R68 points together (enable drive the RESET pin through RESET test point)
Unsolder LK13 and LK14 from position A and solder them in position C (tie MUX_OUT with ADC_IN).
Unsolder SL09 and SL10 from position A and solder each of them to position B to allow the VIN7 signal to bypass the input buffer.

After the changes in the link positions and soldering links, the EVAL-AD7091R-xSDZ evaluation board should look like the following.

There are a number of connections to make between the ADC evaluation board and the Linux machine.

EVAL-AD7091R-xSDZ test point	Pin Function	RPI-4 Pin function (Pin number)
CS	Chip Select	CE0 (pin 24)
SCLK	Serial Clock	SCLK (pin 23)
SDO	Serial Data Out	MISO (pin 21)
SDI	Serial Data In	MOSI (pin 19)
RESET	ADC Reset	GPIO 27 (pin 13)
CONVST	Conversion Start Signal	GPIO 25 (pin 22)
VDRIVE (J4)	Digital Supply Voltage Input	3.3V (pin 17
GND (J4)	Digital Supply Voltage Ground	GND (pin 20)
VDD (J9)	Power Supply Input	3.3V (pin 1)
GND (J9)	Power Supply Ground	GND (pin 6)

Where J4 is the external VDRIVE and GND power connector and J9 is the external VDD and GND power connector.

Here is how it looks after everything is connected.

The collection of jumpers looks messy and hard to follow so review the textual description in case of doubt.

Adding Linux driver support

Enabling the driver

Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)

The AD7091R8 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Analog to digital converters  ---> 
                ...
                <*>   Analog Devices AD7091R8 ADC driver
                ...
            ...
        ...

Adding a device tree entry

Required properties

compatible: Must be one of “adi,ad7091r2”, “adi,ad7091r4”, “adi,ad7091r8”.
reg: number of SPI chip select id for the device.
adi,conversion-start-gpios: Device tree identifier of the CONVST pin.
reset-gpios: Device tree identifier of the RESET pin.

Optional properties

vref-supply: phandle + specifier to a regulator for the external VREF supply. If no external VREF is supplied this attribute should be omitted.
see: Documentation/devicetree/bindings/regulator/regulator.txt

Device tree generic example

    #include <dt-bindings/interrupt-controller/irq.h>
    #include <dt-bindings/gpio/gpio.h>
    spi {
        #address-cells = <1>;
        #size-cells = <0>;

        adc@0 {
                compatible = "adi,ad7091r8";
                reg = <0x0>;
                spi-max-frequency = <45454545>;
                vref-supply = <&adc_vref>;
                adi,conversion-start-gpios = <&gpio 25 GPIO_ACTIVE_LOW>;
                reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
                interrupts = <22 IRQ_TYPE_EDGE_FALLING>;
                interrupt-parent = <&gpio>;
        };
    };

Device tree overlay example

// SPDX-License-Identifier: GPL-2.0

/dts-v1/;
/plugin/;

#include <dt-bindings/interrupt-controller/irq.h>
#include <dt-bindings/gpio/gpio.h>

/ {
	compatible = "brcm,bcm2835", "brcm,bcm2711";
};

&gpio {
	ad7091r8_pins: ad7091r8_pins {
		brcm,pins = <22>; // interrupt
		brcm,function = <0>; // input
	};
};

&spi0 {
	status = "okay";

	cs-gpios = <&gpio 8 GPIO_ACTIVE_LOW>;

	ad7091r8@0 {
		compatible = "adi,ad7091r8";
		reg = <0x0>;
		spi-max-frequency = <1000000>;
		adi,conversion-start-gpios = <&gpio 25 GPIO_ACTIVE_LOW>;
		reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
		pinctrl-names = "default";
		pinctrl-0 = <&ad7091r8_pins>;
		interrupt-parent = <&gpio>;
		interrupts = <22 IRQ_TYPE_EDGE_FALLING>;
	};
};

&spidev0 {
	status = "disabled";
};

&spidev1 {
	status = "disabled";
};

Driver testing

Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.

02 Mar 2011 15:16

TIP: An example program whiroot@analog:/sys/bus/iio/devices# ls -lch uses the interface can be found here:

IIO Oscilloscope