This version (24 Mar 2021 13:52) was approved by Michael Hennerich.The Previously approved version (24 Mar 2021 09:20) is available.Diff

AD8366 Dual-Digital Variable Gain Amplifier Linux Driver

Supported Devices

Evaluation Boards


This is a Linux industrial I/O (IIO) subsystem driver, targeting serial interface VGA/PGA amplifiers. The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc). See IIO for more information.

Source Code


Source Mainlined?
git Yes


Declaring SPI slave devices

Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.

This method is appropriate when the SPI bus is a system bus, as in many embedded systems, wherein each SPI bus has a number which is known in advance. It is thus possible to pre-declare the SPI devices that inhabit this bus. This is done with an array of struct spi_board_info, which is registered by calling spi_register_board_info().

For more information see: Documentation/spi/spi-summary.rst

21 Oct 2010 16:10

Depending on the IC used, you may need to set the modalias accordingly, matching your part name. It may also required to adjust max_speed_hz. Please consult the datasheet, for maximum spi clock supported by the device in question.

static struct spi_board_info board_spi_board_info[] __initdata = {
#if defined(CONFIG_AD8366) || defined(CONFIG_AD8366_MODULE)
		.modalias = "ad8366",
		.max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0,
		.chip_select = 6,
		.platform_data = &ad8366_pdata_lpc, /* spi_driver specific config */
		.mode = SPI_MODE_0, /* optional set SPI_3WIRE */
static int __init board_init(void)
	spi_register_board_info(board_spi_board_info, ARRAY_SIZE(board_spi_board_info));
	return 0;

Example SPI device devicetree initialization

Analog Devices AD8366 (and similar) VGAs and DSAs

Required properties:

  • compatible: Must be one of:
    • “adi,ad8366”,
    • “adi,ada4961”,
    • “adi,adrf5720”,
    • “adi,adrf5730”,
    • “adi,adrf5731”,
    • “adi,adl5240”,
    • “adi,hmc271”,
    • “adi,hmc1018a”,
    • “adi,hmc1019a”,
    • “adi,hmc1119”,
  • reg: SPI chip select number for the device
  • #address-cells: Must be set to 1
  • #size-cells: Must be set to 0
  • spi-max-frequency: See Documentation/devicetree/bindings/spi/spi-bus.txt
  • spi-cpha: See Documentation/devicetree/bindings/spi/spi-bus.txt
  • spi-cpol: See Documentation/devicetree/bindings/spi/spi-bus.txt

Optional properties:

  • reset-gpio: a GPIO spec for the RESET pin (if available).
  • enable-gpio: a GPIO spec for the ENABLE or serial interface select pin (S/A) (if available).


&spi0 {
	status = "okay";
        hmc1018a: hmc1018a@0 {
		#address-cells = <1>;
		#size-cells = <0>;
		compatible = "adi,hmc1018a";
		reg = <0>;
		spi-max-frequency = <1000000>;
        adrf5720: adrf5731@1 {
		#address-cells = <1>;
		#size-cells = <0>;
		compatible = "adi,adrf5731";
		reg = <1>;
		spi-max-frequency = <1000000>;
	vga0_ad8366: ad8366@6 {
		#address-cells = <1>;
		#size-cells = <0>;
		compatible = "adi,ad8366";
		reg = <6>;
		spi-max-frequency = <10000000>;

Adding Linux driver support

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

The AD8366 Driver depends on CONFIG_SPI

Linux Kernel Configuration
	Device Drivers  --->
		<*>     Industrial I/O support --->
		    --- Industrial I/O support
				Amplifiers  --->
					<*> Analog Devices AD8366 VGA

Hardware configuration

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

This specifies any shell prompt running on the target

root:/> cd /sys/bus/iio/devices/
root:/sys/bus/iio/devices> ls
root:/sys/bus/iio/devices> iio:device0

root:/> ls -l
drwxr-xr-x    2 root     root             0 Jan  1 00:00 .
drwxr-xr-x    3 root     root             0 Jan  1 00:00 ..
-r--r--r--    1 root     root          4096 Jan  1 00:00 dev
-r--r--r--    1 root     root          4096 Jan  1 00:00 name
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage0_hardwaregain
-rw-r--r--    1 root     root          4096 Jan  1 00:00 out_voltage1_hardwaregain
lrwxrwxrwx    1 root     root             0 Jan  1 00:00 subsystem -> ../../../../../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  1 00:00 uevent

Show device name

This specifies any shell prompt running on the target

root:/> cd /sys/bus/iio/devices/iio\:device0/
root:/> cat name

Set ChannelY Gain


Hardware applied gain factor. If shared across all channels, <type>_hardwaregain is used.

This specifies any shell prompt running on the target

root:/> cat out_voltage0_hardwaregain
4.500000 dB

root:/> echo 10 > out_voltage0_hardwaregain
root:/> cat out_voltage0_hardwaregain
9.813000 dB

More Information

resources/tools-software/linux-drivers/iio-amplifiers/ad8366.txt · Last modified: 24 Mar 2021 13:52 by Michael Hennerich