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Documentation: iio: Add AD7768 Documentation
Add driver documentation for AD7768 Signed-off-by: Janani Sunil <janani.sunil@analog.com>
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‎Documentation/iio/ad7768.rst‎

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.. SPDX-License-Identifier: GPL-2.0-only
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=============
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AD7768 driver
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=============
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ADC driver for Analog Devices Inc. AD7768 and AD7768-4 devices. The module name
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is ``ad7768``.
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Supported devices
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=================
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The following chips are supported by this driver:
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* `AD7768 <https://www.analog.com/en/products/ad7768.html>`_ - 8-channel, 24-bit simultaneous sampling ADC
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* `AD7768-4 <https://www.analog.com/en/products/ad7768-4.html>`_ - 4-channel, 24-bit simultaneous sampling ADC
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Supported features
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==================
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Power modes
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-----------
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The AD7768 family supports three configurable power and performance modes:
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* **Low power mode** - Optimized for lowest power consumption
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* **Median mode** - Balanced power and performance
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* **Fast mode** - Highest performance with maximum sampling rates
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The power mode affects the available sampling frequencies and power consumption.
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Set via the ``adi,power-mode`` device tree property.
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Data output configuration
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-------------------------
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The devices support flexible serial data output configurations:
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AD7768 data lines
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^^^^^^^^^^^^^^^^^
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* 1 data line (DOUT0) - Standard single-lane output
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* 2 data lines (DOUT0, DOUT1) - Dual-lane output for higher throughput
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* 8 data lines (DOUT0-DOUT7) - Maximum throughput, one line per channel
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AD7768-4 data lines
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^^^^^^^^^^^^^^^^^^^
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* 1 data line (DOUT0) - Standard single-lane output
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* 4 data lines (DOUT0-DOUT3) - Maximum throughput, one line per channel
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The number of data lines is configured via the ``adi,data-lines-number``
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device tree property.
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Channel configuration
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---------------------
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Each channel can be individually configured with:
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Channel modes
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^^^^^^^^^^^^^
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* **Mode A** - First set of filter and decimation settings
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* **Mode B** - Second set of filter and decimation settings
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Each channel can be assigned to either Mode A or Mode B via the
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``adi,ch-mode`` device tree property.
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Precharge and reference buffers
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Per-channel buffer control for optimal signal integrity:
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* Positive input precharge buffer (``adi,prebuf-pos-en``)
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* Negative input precharge buffer (``adi,prebuf-neg-en``)
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* Positive reference buffer (``adi,refbuf-pos-en``)
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* Negative reference buffer (``adi,refbuf-neg-en``)
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Common mode voltage
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-------------------
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Configurable common mode output voltage levels:
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* (AVDD - AVSS) / 2V
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* 1.65V
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* 2.5V
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* 2.14V
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Set via the ``adi,common-mode-output-v`` device tree property.
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The common mode buffer can be powered down using ``adi,vcm-power-down``.
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Filter types
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------------
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Two digital filter types are available:
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* **Wideband** - Optimized for wide bandwidth applications
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* **Sinc5** - Fifth-order sinc filter for high rejection of out-of-band noise
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IIO backend support
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-------------------
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The driver integrates with IIO backends (e.g., AXI ADC) for high-speed data
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capture and DMA operations. Features include:
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* Automatic channel enable/disable based on scan mask
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* CRC on data interface. CRC replaces the header every 4th output sample.
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* High-throughput buffered data acquisition
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GPIO controller
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---------------
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The AD7768 includes a 5-pin GPIO controller for auxiliary digital I/O
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operations. The GPIO pins can be configured as inputs or outputs.
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Device attributes
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=================
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The following IIO attributes are available for each enabled channel:
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Channel data
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------------
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage<N>_raw`` | Raw ADC voltage value for channel N. |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage<N>_scale`` | Scale factor to convert raw value to mV. |
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+---------------------------------------+--------------------------------------------------------------+
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Sampling frequency
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------------------
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage<N>_sampling_frequency`` | Current sampling frequency in Hz for channel N. |
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+---------------------------------------+--------------------------------------------------------------+
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Filter configuration
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---------------------
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage<N>_filter_type`` | Current filter type for channel N: "wideband" or "sinc5". |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage<N>_filter_type_ | Available filter types for channel N: "wideband sinc5". |
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| available`` | |
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+---------------------------------------+--------------------------------------------------------------+
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Per-channel calibration
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-----------------------
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+---------------------------------------+--------------------------------------------------------------+
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| Attribute | Description |
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+=======================================+==============================================================+
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| ``in_voltage<N>_calibbias`` | Channel offset calibration value |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage<N>_calibscale`` | Channel gain calibration value |
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+---------------------------------------+--------------------------------------------------------------+
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| ``in_voltage<N>_phase`` | Channel phase calibration value. |
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+---------------------------------------+--------------------------------------------------------------+
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Device buffers
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==============
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This driver supports IIO buffered data acquisition through IIO backends.
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When used with compatible backends like the AXI ADC, it provides:
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* High-speed simultaneous sampling across all enabled channels
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* Hardware-triggered data capture
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* DMA-based data transfer for minimal CPU overhead
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* CRC error detection and correction
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See :doc:`iio_devbuf` for more information about IIO device buffers.
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Example usage
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=============
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.. code-block:: bash
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# Read current sampling frequency for channel 0
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cat /sys/bus/iio/devices/iio:device0/in_voltage0_sampling_frequency
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# Update sampling frequency for channel 0
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echo 8000 > /sys/bus/iio/devices/iio:device0/in_voltage0_sampling_frequency
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# Read current filter type for channel 0
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cat /sys/bus/iio/devices/iio:device0/in_voltage0_filter_type
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# List available filter types for channel 0
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cat /sys/bus/iio/devices/iio:device0/in_voltage0_filter_type_available
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# Update filter type for channel 0 to wideband
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echo wideband > /sys/bus/iio/devices/iio:device0/in_voltage0_filter_type
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# Read calibration scale for channel 0
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cat /sys/bus/iio/devices/iio:device0/in_voltage0_calibscale
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# Read phase calibration for channel 0
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cat /sys/bus/iio/devices/iio:device0/in_voltage0_phase
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Unimplemented features
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======================
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* CRC message every 16 samples (CRC_SEL configuration) - currently only supports CRC every 4 samples

‎Documentation/iio/index.rst‎

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