.. SPDX-License-Identifier: GPL-2.0-only

=============
AD7380 driver
=============

ADC driver for Analog Devices Inc. AD7380 and similar devices. The module name
is ``ad7380``.


Supported devices
=================

The following chips are supported by this driver:

* `AD7380 <https://www.analog.com/en/products/ad7380.html>`_
* `AD7381 <https://www.analog.com/en/products/ad7381.html>`_
* `AD7383 <https://www.analog.com/en/products/ad7383.html>`_
* `AD7384 <https://www.analog.com/en/products/ad7384.html>`_
* `AD7386 <https://www.analog.com/en/products/ad7386.html>`_
* `AD7387 <https://www.analog.com/en/products/ad7387.html>`_
* `AD7388 <https://www.analog.com/en/products/ad7388.html>`_
* `AD7380-4 <https://www.analog.com/en/products/ad7380-4.html>`_
* `AD7381-4 <https://www.analog.com/en/products/ad7381-4.html>`_
* `AD7383-4 <https://www.analog.com/en/products/ad7383-4.html>`_
* `AD7384-4 <https://www.analog.com/en/products/ad7384-4.html>`_
* `AD7386-4 <https://www.analog.com/en/products/ad7386-4.html>`_
* `AD7387-4 <https://www.analog.com/en/products/ad7387-4.html>`_
* `AD7388-4 <https://www.analog.com/en/products/ad7388-4.html>`_
* `ADAQ4370-4 <https://www.analog.com/en/products/adaq4370-4.html>`_
* `ADAQ4380-4 <https://www.analog.com/en/products/adaq4380-4.html>`_
* `ADAQ4381-4 <https://www.analog.com/en/products/adaq4381-4.html>`_


Supported features
==================

SPI wiring modes
----------------

ad738x ADCs can output data on several SDO lines (1/2/4). The driver currently
supports only 1 SDO line.

Reference voltage
-----------------

ad7380-4
~~~~~~~~

ad7380-4 supports only an external reference voltage (2.5V to 3.3V). It must be
declared in the device tree as ``refin-supply``.

ADAQ devices
~~~~~~~~~~~~

ADAQ devices don't have an external reference, but use a 3.3V internal reference
derived from one of its supplies (``refin-supply``)

All other devices from ad738x family
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

All other devices from ad738x support 2 possible reference voltage sources:

- Internal reference (2.5V)
- External reference (2.5V to 3.3V)

The source is determined by the device tree. If ``refio-supply`` is present,
then it is used as external reference, else the internal reference is used.

Oversampling and resolution boost
---------------------------------

This family supports 2 types of oversampling: normal average and rolling
average. Only normal average is supported by the driver, as rolling average can
be achieved by processing a captured data buffer. The following ratios are
available: 1 (oversampling disabled)/2/4/8/16/32.

When the on-chip oversampling function is enabled the performance of the ADC can
exceed the default resolution. To accommodate the performance boost achievable,
it is possible to enable an additional two bits of resolution. Because the
resolution boost feature can only be enabled when oversampling is enabled and
oversampling is not as useful without the resolution boost, the driver
automatically enables the resolution boost if and only if oversampling is
enabled.

Since the resolution boost feature causes 16-bit chips to now have 18-bit data
which means the storagebits has to change from 16 to 32 bits, we use the new
ext_scan_type feature to allow changing the scan_type at runtime. Unfortunately
libiio does not support it. So when enabling or disabling oversampling, user
must restart iiod using the following command:

.. code-block:: bash

	root:~# systemctl restart iiod

Alert
-----

2 channels variants of the ad738x family, can use the SDOB line as an alert pin
when configured in 1 SDO line mode. 4 channels variants, can use SDOD as an
alert pin when configured in 1 or 2 SDO line(s) mode, although only 1 SDO line
mode is currently supported by the driver (see `SPI wiring modes`_).

At the end of a conversion the active-low alert pin gets asserted if the
conversion result exceeds the alert high limit or falls below the alert low
limit. It is cleared, on a falling edge of CS. The alert pin is common to all
channels.

User can enable alert using the regular iio events attribute:

.. code-block:: bash

	events/thresh_either_en

The high and low thresholds are common to all channels and can also be set using
regular iio events attributes:

.. code-block:: bash

	events/in_thresh_falling_value
	events/in_thresh_rising_value

If debugfs is available, user can read the ALERT register to determine the
faulty channel and direction.

In most use cases, user will hardwire the alert pin to trigger a shutdown.

Channel selection and sequencer (single-end chips only)
-------------------------------------------------------

Single-ended chips of this family (ad7386/7/8(-4)) have a 2:1 multiplexer in
front of each ADC. They also include additional configuration registers that
allow for either manual selection or automatic switching (sequencer mode), of
the multiplexer inputs.

From an IIO point of view, all inputs are exported, i.e ad7386/7/8
export 4 channels and ad7386-4/7-4/8-4 export 8 channels.

Inputs ``AinX0`` of multiplexers correspond to the first half of IIO channels (i.e
0-1 or 0-3) and inputs ``AinX1`` correspond to second half (i.e 2-3 or 4-7).
Example for AD7386/7/8 (2 channels parts):

.. code-block::

	   IIO   | AD7386/7/8
	         |         +----------------------------
	         |         |     _____        ______
	         |         |    |     |      |      |
	voltage0 | AinA0 --|--->|     |      |      |
	         |         |    | mux |----->| ADCA |---
	voltage2 | AinA1 --|--->|     |      |      |
	         |         |    |_____|      |_____ |
	         |         |     _____        ______
	         |         |    |     |      |      |
	voltage1 | AinB0 --|--->|     |      |      |
	         |         |    | mux |----->| ADCB |---
	voltage3 | AinB1 --|--->|     |      |      |
	         |         |    |_____|      |______|
	         |         |
	         |         +----------------------------


When enabling sequencer mode, the effective sampling rate is divided by two.

Gain (ADAQ devices only)
~~~~~~~~~~~~~~~~~~~~~~~~

ADAQ devices have a pin selectable gain in front of each ADC. The appropriate
gain is selectable from device tree using the ``adi,gain-milli`` property.
Refer to the typical connection diagrams section of the datasheet for pin
wiring.

Unimplemented features
----------------------

- 2/4 SDO lines
- Rolling average oversampling
- Power down mode
- CRC indication

SPI offload support
===================

To be able to achieve the maximum sample rate, the driver can be used with the
`AXI SPI Engine`_ to provide SPI offload support.

.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/pulsar_adc/index.html

When SPI offload is being used, some attributes will be different.

* ``trigger`` directory is removed.
* ``in_voltage0_sampling_frequency`` attribute is added for setting the sample
  rate.
* ``in_voltage0_sampling_frequency_available`` attribute is added for querying
  the max sample rate.
* ``timestamp`` channel is removed.
* Buffer data format may be different compared to when offload is not used,
  e.g. the ``in_voltage0_type`` attribute.

Device buffers
==============

This driver supports IIO triggered buffers.

See :doc:`iio_devbuf` for more information.
