Documentation/iio/ad7380.rst

   1 .. SPDX-License-Identifier: GPL-2.0-only
   2
   3 =============
   4 AD7380 driver
   5 =============
   6
   7 ADC driver for Analog Devices Inc. AD7380 and similar devices. The module name
   8 is ``ad7380``.
   9
  10
  11 Supported devices
  12 =================
  13
  14 The following chips are supported by this driver:
  15
  16 * `AD7380 <https://www.analog.com/en/products/ad7380.html>`_
  17 * `AD7381 <https://www.analog.com/en/products/ad7381.html>`_
  18 * `AD7383 <https://www.analog.com/en/products/ad7383.html>`_
  19 * `AD7384 <https://www.analog.com/en/products/ad7384.html>`_
  20 * `AD7386 <https://www.analog.com/en/products/ad7386.html>`_
  21 * `AD7387 <https://www.analog.com/en/products/ad7387.html>`_
  22 * `AD7388 <https://www.analog.com/en/products/ad7388.html>`_
  23 * `AD7380-4 <https://www.analog.com/en/products/ad7380-4.html>`_
  24 * `AD7381-4 <https://www.analog.com/en/products/ad7381-4.html>`_
  25 * `AD7383-4 <https://www.analog.com/en/products/ad7383-4.html>`_
  26 * `AD7384-4 <https://www.analog.com/en/products/ad7384-4.html>`_
  27 * `AD7386-4 <https://www.analog.com/en/products/ad7386-4.html>`_
  28 * `AD7387-4 <https://www.analog.com/en/products/ad7387-4.html>`_
  29 * `AD7388-4 <https://www.analog.com/en/products/ad7388-4.html>`_
  30
  31
  32 Supported features
  33 ==================
  34
  35 SPI wiring modes
  36 ----------------
  37
  38 ad738x ADCs can output data on several SDO lines (1/2/4). The driver currently
  39 supports only 1 SDO line.
  40
  41 Reference voltage
  42 -----------------
  43
  44 2 possible reference voltage sources are supported:
  45
  46 - Internal reference (2.5V)
  47 - External reference (2.5V to 3.3V)
  48
  49 The source is determined by the device tree. If ``refio-supply`` is present,
  50 then the external reference is used, else the internal reference is used.
  51
  52 Oversampling and resolution boost
  53 ---------------------------------
  54
  55 This family supports 2 types of oversampling: normal average and rolling
  56 average. Only normal average is supported by the driver, as rolling average can
  57 be achieved by processing a captured data buffer. The following ratios are
  58 available: 1 (oversampling disabled)/2/4/8/16/32.
  59
  60 When the on-chip oversampling function is enabled the performance of the ADC can
  61 exceed the default resolution. To accommodate the performance boost achievable,
  62 it is possible to enable an additional two bits of resolution. Because the
  63 resolution boost feature can only be enabled when oversampling is enabled and
  64 oversampling is not as useful without the resolution boost, the driver
  65 automatically enables the resolution boost if and only if oversampling is
  66 enabled.
  67
  68 Since the resolution boost feature causes 16-bit chips to now have 18-bit data
  69 which means the storagebits has to change from 16 to 32 bits, we use the new
  70 ext_scan_type feature to allow changing the scan_type at runtime. Unfortunately
  71 libiio does not support it. So when enabling or disabling oversampling, user
  72 must restart iiod using the following command:
  73
  74 .. code-block:: bash
  75
  76         root:~# systemctl restart iiod
  77
  78 Channel selection and sequencer (single-end chips only)
  79 -------------------------------------------------------
  80
  81 Single-ended chips of this family (ad7386/7/8(-4)) have a 2:1 multiplexer in
  82 front of each ADC. They also include additional configuration registers that
  83 allow for either manual selection or automatic switching (sequencer mode), of
  84 the multiplexer inputs.
  85
  86 From an IIO point of view, all inputs are exported, i.e ad7386/7/8
  87 export 4 channels and ad7386-4/7-4/8-4 export 8 channels.
  88
  89 Inputs ``AinX0`` of multiplexers correspond to the first half of IIO channels (i.e
  90 0-1 or 0-3) and inputs ``AinX1`` correspond to second half (i.e 2-3 or 4-7).
  91 Example for AD7386/7/8 (2 channels parts):
  92
  93 .. code-block::
  94
  95            IIO   | AD7386/7/8
  96                  |         +----------------------------
  97                  |         |     _____        ______
  98                  |         |    |     |      |      |
  99         voltage0 | AinA0 --|--->|     |      |      |
 100                  |         |    | mux |----->| ADCA |---
 101         voltage2 | AinA1 --|--->|     |      |      |
 102                  |         |    |_____|      |_____ |
 103                  |         |     _____        ______
 104                  |         |    |     |      |      |
 105         voltage1 | AinB0 --|--->|     |      |      |
 106                  |         |    | mux |----->| ADCB |---
 107         voltage3 | AinB1 --|--->|     |      |      |
 108                  |         |    |_____|      |______|
 109                  |         |
 110                  |         +----------------------------
 111
 112
 113 When enabling sequencer mode, the effective sampling rate is divided by two.
 114
 115 Unimplemented features
 116 ----------------------
 117
 118 - 2/4 SDO lines
 119 - Rolling average oversampling
 120 - Power down mode
 121 - CRC indication
 122 - Alert
 123
 124
 125 Device buffers
 126 ==============
 127
 128 This driver supports IIO triggered buffers.
 129
 130 See :doc:`iio_devbuf` for more information.