AD5360

AD5360 IIO Multi-Channel DAC Linux Driver.

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting multi-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 Linux Industrial I/O Subsystem for more information.

Source Code

Status

Source

Mainlined?

git

Yes

Files

Function

File

driver

drivers/iio/dac/ad5360.c

Example device tree

fragment@0 {
    target-path = "/";
    __overlay__ {
        vref0: fixedregulator@0 {
            compatible = "regulator-fixed";
            regulator-name = "fixed-supply0";
            regulator-min-microvolt = <3000000>;
            regulator-max-microvolt = <3000000>;
            regulator-boot-on;
        };
        vref1: fixedregulator@1 {
            compatible = "regulator-fixed";
            regulator-name = "fixed-supply1";
            regulator-min-microvolt = <3000000>;
            regulator-max-microvolt = <3000000>;
            regulator-boot-on;
        };
    };
};

fragment@1 {
    target = <&spi0>;
    __overlay__ {
        #address-cells = <1>;
        #size-cells = <0>;
        status = "okay";

        ad5370@0{
            compatible = "adi,ad5370";
            reg = <0>;
            spi-max-frequency = <1000000>;
            spi-cpha;
            vref0-supply = <&vref0>;
            vref1-supply = <&vref1>;
        };
    };
};

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) In this example all 4 reference voltage are supplied by the same regulator.

Except for the AD5371 devices expect two supplies named vref0 and vref1. The AD5371 expects a third supply named vref2.

#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
static struct regulator_consumer_supply ad5360_consumer_supplies[] = {
    REGULATOR_SUPPLY("vref0", "spi0.3"),
    REGULATOR_SUPPLY("vref1", "spi0.3"),
    REGULATOR_SUPPLY("vref2", "spi0.3"),
};

static struct regulator_init_data stamp_avdd_reg_init_data = {
    .constraints    = {
        .name   = "2V5",
        .valid_ops_mask = REGULATOR_CHANGE_STATUS,
    },
    .consumer_supplies = ad5360_consumer_supplies,
    .num_consumer_supplies = ARRAY_SIZE(ad5360_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,
    },
};
#endif

static struct platform_device *board_devices[] __initdata = {
#if defined(CONFIG_REGULATOR_FIXED_VOLTAGE) || defined(CONFIG_REGULATOR_FIXED_VOLTAGE_MODULE)
    &brd_voltage_regulator
#endif
};

static int __init board_init(void)
{
    [--snip--]

    platform_add_devices(board_devices, ARRAY_SIZE(board_devices));

    [--snip--]

    return 0;
}
arch_initcall(board_init);

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: Overview of Linux kernel SPI support

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 = {
#if defined(CONFIG_AD5360_SPI) || \
    defined(CONFIG_AD5360_SPI_MODULE)
    {
        /* the modalias must be the same as spi device driver name */
        .modalias = "ad5360", /* 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_1,
    },
#endif
};

static int __init board_init(void)
{
    [--snip--]

    spi_register_board_info(board_spi_board_info, ARRAY_SIZE(board_spi_board_info));

    [--snip--]

    return 0;
}
arch_initcall(board_init);

Adding Linux driver support

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

Note

The AD5360 Driver depends on CONFIG_SPI

Linux Kernel Configuration
    Device Drivers  --->
        ...
        <*>     Industrial I/O support --->
            --- Industrial I/O support
            ...
            Digital to analog converters  --->
                ...
                <*>  Analog Devices Analog Devices AD5360/61/62/63/70/71/73 DAC driver
                ...
            ...
        ...

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.

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

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  2 21:54 dev
-r--r--r--    1 root     root          4096 Jan  2 21:54 name
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage0_scale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_calibbias
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_calibscale
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_offset
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_raw
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage10_scale
...
-rw-r--r--    1 root     root          4096 Jan  2 21:54 out_voltage_powerdown
drwxr-xr-x    2 root     root             0 Jan  2 21:54 power
lrwxrwxrwx    1 root     root             0 Jan  2 21:54 subsystem -> ../../../../../bus/iio
-rw-r--r--    1 root     root          4096 Jan  2 21:54 uevent

Show device name

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat name
ad5360

Show scale

Description:
/sys/bus/iio/devices/iio:deviceX/out_voltageY_scale

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

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage0_scale
0.038140
Set channel Y output voltage

Description: /sys/bus/iio/devices/iio:deviceX/out_voltageY_raw

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

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 10000 > out_voltage0_raw

U = out_voltage0_raw * out_voltage0_scale = 10000 * 0,038140 mV = 381,14 mV

Calibrate channel Y gain

Description: /sys/bus/iio/devices/iio:deviceX/out_voltageY_calibscale

Each channel has an adjustable gain which can be used to calibrate the channel’s scale and compensate for full-scale errors. The default value is 65535.

If scale calibration is used the following formula can be used calculate the output voltage: U = ( ( out_voltageY_raw * ( out_voltageY_calibscale + 1 ) ) / 2^16 - out_voltageY_calibbias ) * out_voltageY_scale

Calibrate channel Y offset

Description: /sys/bus/iio/devices/iio:deviceX/out_voltageY_calibbias

Each channel has an adjustable offset which can be used to calibrate the channel’s offset and compensate for zero-scale errors. The default value is 0.

If offset calibration is used the following formula can be used calculate the output voltage: U = ( ( out_voltageY_raw * ( out_voltageY_calibscale + 1 ) ) / 2^16 - out_voltageY_calibbias ) * out_voltageY_scale

Enable power down mode for the device

/sys/bus/iio/devices/iio:deviceX/out_voltage_powerdown

Description: Writing 1 causes the device to enter power down mode. Clearing returns to normal operation.

root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 1 > out_voltage_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown
1
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> echo 0 > out_voltage_powerdown
root:/sys/devices/platform/bfin-spi.0/spi0.3/iio:device0> cat out_voltage_powerdown
0

More Information