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The Analog Devices Inc. AD7606 (and similar chips) are complex ADCs that will benefit from a detailed driver documentation. This documents the current features supported by the driver. Signed-off-by: Guillaume Stols <gstols@baylibre.com> Link: https://patch.msgid.link/20241015-ad7606_add_iio_backend_support-v5-3-654faf1ae08c@baylibre.com Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
145 lines
5.0 KiB
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145 lines
5.0 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
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=============
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AD7606 driver
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=============
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ADC driver for Analog Devices Inc. AD7606 and similar devices. The module name
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is ``ad7606``.
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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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* `AD7605 <https://www.analog.com/en/products/ad7605.html>`_
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* `AD7606 <https://www.analog.com/en/products/ad7606.html>`_
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* `AD7606B <https://www.analog.com/en/products/ad7606b.html>`_
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* `AD7616 <https://www.analog.com/en/products/ad7616.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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These ADCs can output data on several SDO lines (1/2/4/8). The driver
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currently supports only 1 SDO line.
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Parallel wiring mode
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--------------------
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There is also a parallel interface, with 16 lines (that can be reduced to 8 in
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byte mode). The parallel interface is selected by declaring the device as
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platform in the device tree (with no io-backends node defined, see below).
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IIO-backend mode
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----------------
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This mode allows to reach the best sample rates, but it requires an external
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hardware (eg HDL or APU) to handle the low level communication.
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The backend mode is enabled when through the definition of the "io-backends"
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property in the device tree.
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The reference configuration for the current implementation of IIO-backend mode
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is the HDL reference provided by ADI:
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https://wiki.analog.com/resources/eval/user-guides/ad7606x-fmc/hdl
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This implementation embeds an IIO-backend compatible IP (adi-axi-adc) and a PWM
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connected to the conversion trigger pin.
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.. code-block::
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+---+ +----------------------------
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| | +-------+ |AD76xx
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| A | controls | | |
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| D |-------------->| PWM |-------------->| cnvst
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| 7 | | | |
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| 6 | +-------+ |
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| 0 | controls +-----------+-----------+ |
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| 6 |---------->| | |<--| frstdata
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| | | Backend | Backend |<--| busy
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| D | | Driver | | |
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| R | | | |-->| clk
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| I | requests |+---------+| DMA | |
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| V |----------->| Buffer ||<---- |<=>| DATA
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| E | |+---------+| | |
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| R | +-----------+-----------+ |
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| |-------------------------------------->| reset/configuration gpios
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+---+ +-----------------------------
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Software and hardware modes
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---------------------------
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While all the AD7606/AD7616 series parts can be configured using GPIOs, some of
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them can be configured using register.
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The chips that support software mode have more values available for configuring
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the device, as well as more settings, and allow to control the range and
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calibration per channel.
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The following settings are available per channel in software mode:
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- Scale
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Also, there is a broader choice of oversampling ratios in software mode.
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Conversion triggering
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---------------------
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The conversion can be triggered by two distinct ways:
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- A GPIO is connected to the conversion trigger pin, and this GPIO is controlled
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by the driver directly. In this configuration, the driver sets back the
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conversion trigger pin to high as soon as it has read all the conversions.
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- An external source is connected to the conversion trigger pin. In the
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current implementation, it must be a PWM. In this configuration, the driver
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does not control directly the conversion trigger pin. Instead, it can
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control the PWM's frequency. This trigger is enabled only for iio-backend.
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Reference voltage
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-----------------
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2 possible reference voltage sources are supported:
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- Internal reference (2.5V)
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- External reference (2.5V)
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The source is determined by the device tree. If ``refin-supply`` is present,
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then the external reference is used, otherwise the internal reference is used.
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Oversampling
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------------
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This family supports oversampling to improve SNR.
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In software mode, the following ratios are available:
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1 (oversampling disabled)/2/4/8/16/32/64/128/256.
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Unimplemented features
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----------------------
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- 2/4/8 SDO lines
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- CRC indication
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- Calibration
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Device buffers
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==============
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IIO triggered buffer
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--------------------
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This driver supports IIO triggered buffers, with a "built in" trigger, i.e the
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trigger is allocated and linked by the driver, and a new conversion is triggered
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as soon as the samples are transferred, and a timestamp channel is added to make
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up for the potential jitter induced by the delays in the interrupt handling.
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IIO backend buffer
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------------------
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When IIO backend is used, the trigger is not needed, and the sample rate is
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considered as stable. There is no timestamp channel. The communication is
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delegated to an external logic, called a backend, and the backend's driver
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handles the buffer. When this mode is enabled, the driver cannot control the
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conversion pin, because the busy pin is bound to the backend.
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