This version (11 Mar 2015 10:12) was approved by larsc.The Previously approved version (06 Feb 2014 12:10) is available.Diff

AD5449 IIO DAC Linux Driver

Supported Devices

Reference Circuits

Evaluation Boards


This is a Linux industrial I/O (IIO) subsystem driver, targeting single channel serial interface DACs. 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


Example platform device initialization

Specifying reference voltage via the regulator framework

Below example specifies a 2.5 Volt reference for the SPI device 3 on SPI-Bus 0. (spi0.3)

static struct regulator_consumer_supply ad5449_consumer_supplies[] = {
	REGULATOR_SUPPLY("vcc", "spi0.3"),
static struct regulator_init_data stamp_avdd_reg_init_data = {
	.constraints	= {
		.name	= "2V5",
		.valid_ops_mask = REGULATOR_CHANGE_STATUS,
	.consumer_supplies = ad5449_consumer_supplies,
	.num_consumer_supplies = ARRAY_SIZE(ad5449_consumer_supplies),
static struct fixed_voltage_config stamp_vdd_pdata = {
	.supply_name	= "board-2V5",
	.microvolts	= 2500000,
	.gpio		= -EINVAL,
	.enabled_at_boot = 0,
	.init_data	= &stamp_avdd_reg_init_data,
static struct platform_device brd_voltage_regulator = {
	.name		= "reg-fixed-voltage",
	.id		= -1,
	.num_resources	= 0,
	.dev		= {
		.platform_data	= &stamp_vdd_pdata,
static struct platform_device *board_devices[] __initdata = {
static int __init board_init(void)
	platform_add_devices(board_devices, ARRAY_SIZE(board_devices));
	return 0;

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

21 Oct 2010 16:10 · Michael Hennerich

Depending on the converter 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 = {
		/* the modalias must be the same as spi device driver name */
		.modalias = "ad5449", /* Name of spi_driver for this device */
		.max_speed_hz = 1000000,     /* max spi clock (SCK) speed in HZ */
		.bus_num = 0, /* Framework bus number */
		.chip_select = 3, /* Framework chip select */
		.mode = SPI_MODE_2,
static int __init board_init(void)
	spi_register_board_info(board_spi_board_info, ARRAY_SIZE(board_spi_board_info));
	return 0;

Adding Linux driver support

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

The AD5449 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
    <*>     Industrial I/O support --->
        --- Industrial I/O support
        Digital to analog converters  ---> 
            <*>  Analog Devices AD5449 and similar DACs drive

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 · Michael Hennerich

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> cd iio:device0

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> ls -l
-r--r--r--    1 root     root          4096 Jan  1 02:20 dev
-r--r--r--    1 root     root          4096 Jan  1 02:20 name
-rw-r--r--    1 root     root          4096 Jan  1 02:25 out_voltage0_raw
-rw-r--r--    1 root     root          4096 Jan  1 02:20 out_voltage0_scale
-rw-r--r--    1 root     root          4096 Jan  1 02:25 out_voltage1_raw
-rw-r--r--    1 root     root          4096 Jan  1 02:20 out_voltage1_scale
drwxr-xr-x    2 root     root             0 Jan  1 02:20 power
lrwxrwxrwx    1 root     root             0 Jan  1 02:20 subsystem -> ../../../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  1 02:20 uevent

For DACs with only one output channel there will be no out_voltage1_raw and out_voltage1_scale files

Show device name

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name

Show scale

scale to be applied to out_voltage0_raw in order to obtain the measured voltage in millivolts.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_scale

Set channel 0


Raw (unscaled, no bias etc.) output voltage for channel Y.

This specifies any shell prompt running on the target

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1234 > out_voltage0_raw

U = out_voltage0_raw * out_voltage_scale = 1234 * 0.152mV = 187.568 mV

More Information

resources/tools-software/linux-drivers/iio-dac/ad5449.txt · Last modified: 11 Mar 2015 10:12 by larsc