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Adding documentation for adaq4370-4 and adaq4380-4 supported devices. In particular, document the reference voltage mechanism and the gain parameter that are specific to adaq devices. Signed-off-by: Julien Stephan <jstephan@baylibre.com> Reviewed-by: David Lechner <dlechner@baylibre.com> Link: https://patch.msgid.link/20241030-ad7380-add-adaq4380-4-support-v4-5-864ff02babae@baylibre.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
156 lines
5.4 KiB
ReStructuredText
156 lines
5.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
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=============
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AD7380 driver
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=============
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ADC driver for Analog Devices Inc. AD7380 and similar devices. The module name
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is ``ad7380``.
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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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* `AD7380 <https://www.analog.com/en/products/ad7380.html>`_
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* `AD7381 <https://www.analog.com/en/products/ad7381.html>`_
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* `AD7383 <https://www.analog.com/en/products/ad7383.html>`_
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* `AD7384 <https://www.analog.com/en/products/ad7384.html>`_
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* `AD7386 <https://www.analog.com/en/products/ad7386.html>`_
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* `AD7387 <https://www.analog.com/en/products/ad7387.html>`_
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* `AD7388 <https://www.analog.com/en/products/ad7388.html>`_
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* `AD7380-4 <https://www.analog.com/en/products/ad7380-4.html>`_
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* `AD7381-4 <https://www.analog.com/en/products/ad7381-4.html>`_
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* `AD7383-4 <https://www.analog.com/en/products/ad7383-4.html>`_
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* `AD7384-4 <https://www.analog.com/en/products/ad7384-4.html>`_
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* `AD7386-4 <https://www.analog.com/en/products/ad7386-4.html>`_
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* `AD7387-4 <https://www.analog.com/en/products/ad7387-4.html>`_
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* `AD7388-4 <https://www.analog.com/en/products/ad7388-4.html>`_
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* `ADAQ4370-4 <https://www.analog.com/en/products/adaq4370-4.html>`_
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* `ADAQ4380-4 <https://www.analog.com/en/products/adaq4380-4.html>`_
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Supported features
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==================
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SPI wiring modes
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----------------
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ad738x ADCs can output data on several SDO lines (1/2/4). The driver currently
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supports only 1 SDO line.
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Reference voltage
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-----------------
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ad7380-4
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~~~~~~~~
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ad7380-4 supports only an external reference voltage (2.5V to 3.3V). It must be
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declared in the device tree as ``refin-supply``.
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ADAQ devices
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~~~~~~~~~~~~
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adaq4370-4 and adaq4380-4 don't have an external reference, but use a 3.3V
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internal reference derived from one of its supplies (``refin-supply``)
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All other devices from ad738x family
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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All other devices from ad738x support 2 possible reference voltage sources:
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- Internal reference (2.5V)
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- External reference (2.5V to 3.3V)
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The source is determined by the device tree. If ``refio-supply`` is present,
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then it is used as external reference, else the internal reference is used.
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Oversampling and resolution boost
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---------------------------------
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This family supports 2 types of oversampling: normal average and rolling
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average. Only normal average is supported by the driver, as rolling average can
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be achieved by processing a captured data buffer. The following ratios are
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available: 1 (oversampling disabled)/2/4/8/16/32.
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When the on-chip oversampling function is enabled the performance of the ADC can
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exceed the default resolution. To accommodate the performance boost achievable,
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it is possible to enable an additional two bits of resolution. Because the
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resolution boost feature can only be enabled when oversampling is enabled and
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oversampling is not as useful without the resolution boost, the driver
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automatically enables the resolution boost if and only if oversampling is
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enabled.
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Since the resolution boost feature causes 16-bit chips to now have 18-bit data
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which means the storagebits has to change from 16 to 32 bits, we use the new
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ext_scan_type feature to allow changing the scan_type at runtime. Unfortunately
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libiio does not support it. So when enabling or disabling oversampling, user
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must restart iiod using the following command:
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.. code-block:: bash
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root:~# systemctl restart iiod
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Channel selection and sequencer (single-end chips only)
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-------------------------------------------------------
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Single-ended chips of this family (ad7386/7/8(-4)) have a 2:1 multiplexer in
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front of each ADC. They also include additional configuration registers that
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allow for either manual selection or automatic switching (sequencer mode), of
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the multiplexer inputs.
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From an IIO point of view, all inputs are exported, i.e ad7386/7/8
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export 4 channels and ad7386-4/7-4/8-4 export 8 channels.
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Inputs ``AinX0`` of multiplexers correspond to the first half of IIO channels (i.e
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0-1 or 0-3) and inputs ``AinX1`` correspond to second half (i.e 2-3 or 4-7).
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Example for AD7386/7/8 (2 channels parts):
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.. code-block::
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IIO | AD7386/7/8
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| +----------------------------
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| | _____ ______
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| | | | | |
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voltage0 | AinA0 --|--->| | | |
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| | | mux |----->| ADCA |---
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voltage2 | AinA1 --|--->| | | |
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| | |_____| |_____ |
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| | _____ ______
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| | | | | |
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voltage1 | AinB0 --|--->| | | |
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| | | mux |----->| ADCB |---
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voltage3 | AinB1 --|--->| | | |
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| | |_____| |______|
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| |
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| +----------------------------
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When enabling sequencer mode, the effective sampling rate is divided by two.
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Gain (ADAQ devices only)
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~~~~~~~~~~~~~~~~~~~~~~~~
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ADAQ devices have a pin selectable gain in front of each ADC. The appropriate
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gain is selectable from device tree using the ``adi,gain-milli`` property.
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Refer to the typical connection diagrams section of the datasheet for pin
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wiring.
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Unimplemented features
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----------------------
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- 2/4 SDO lines
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- Rolling average oversampling
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- Power down mode
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- CRC indication
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- Alert
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Device buffers
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==============
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This driver supports IIO triggered buffers.
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See :doc:`iio_devbuf` for more information.
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