AD7766

AD7766 24-Bit, 8.5 mW, 109 dB, 128 kSPS/64 kSPS/32 kSPS ADCs IIO Linux Driver.

Supported Devices

Evaluation Boards

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting single channel serial interface ADCs. 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/adc/ad7766.c

Example platform device initialization

For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.

For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.

Specifying reference voltage via the regulator framework

Tip

This driver supports also an alternative way of specifying the reference voltage, by using the Linux regulator framework.

Below example specifies a 5 Volt reference for the SPI device 3 on SPI-Bus 0. (spi0.3)

static struct regulator_consumer_supply ad7766_consumer_supplies[] = {
    REGULATOR_SUPPLY("vref", "spi0.3"),
};

static struct regulator_init_data stamp_avdd_reg_init_data = {
    .constraints    = {
        .name   = "5V0",
        .valid_ops_mask = REGULATOR_CHANGE_STATUS,
    },
    .consumer_supplies = ad7766_consumer_supplies,
    .num_consumer_supplies = ARRAY_SIZE(ad7766_consumer_supplies),
};

static struct fixed_voltage_config stamp_vdd_pdata = {
    .supply_name    = "vref-5V0",
    .microvolts = 5000000,
    .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 = {
    &brd_voltage_regulator
};

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 = {
    {
        /* the modalias must be the same as spi device driver name */
        .modalias = "ad7766", /* 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 */
        .irq = IRQ_PF6,
        .mode = SPI_MODE_3,
    },
};

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 AD7766 Driver depends on CONFIG_SPI_MASTER

Linux Kernel Configuration
    Device Drivers  --->
        -*- Industrial I/O support  --->
                --- Industrial I/O support
                -*-   Enable ring buffer support within IIO
                -*-     Industrial I/O lock free software ring
                -*-   Enable triggered sampling support

                      *** Analog to digital converters ***
                    [--snip--]
                        <*>   Analog Devices AD7766/AD7767 ADC driver
                    [--snip--]

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.

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

/sys/bus/iio/devices/iio:device0> ls -l
drwxrwxrwx 2 root root    0 Jan  1  1970 buffer
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_voltage_scale
-rw-rw-rw- 1 root root 4096 Jan  1  1970 name
-rw-rw-rw- 1 root root 4096 Jan  1  1970 sampling_frequency
drwxrwxrwx 2 root root    0 Jan  1  1970 scan_elements
drwxrwxrwx 2 root root    0 Jan  1  1970 trigger

/sys/bus/iio/devices/iio:device0> ls -l buffer
-rw-rw-rw- 1 root root 4096 Jan  1  1970 enable
-rw-rw-rw- 1 root root 4096 Jan  1  1970 length
-rw-rw-rw- 1 root root 4096 Jan  1  1970 watermark

/sys/bus/iio/devices/iio:device0> ls -l scan_elements
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_timestamp_en
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_timestamp_index
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_timestamp_type
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_voltage0_en
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_voltage0_index
-rw-rw-rw- 1 root root 4096 Jan  1  1970 in_voltage0_type

/sys/bus/iio/devices/iio:device0> ls -l trigger
-rw-rw-rw- 1 root root 4096 Jan  1  1970 current_trigger

Show device name

/sys/bus/iio/devices/iio:device0> cat name
ad7766

Show scale

Description: Scale to be applied to the captured sample data in order to obtain the measured voltage in millivolts.

/sys/bus/iio/devices/iio:device0> cat in_voltage_scale
0.000298023
Show data output rate

Description: Shows the data output rate of the converter in Hz.

/sys/bus/iio/devices/iio:device0> cat sampling_frequency
125000

More Information