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Documentation: iio: ad4000: Describe offload support

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When SPI offloading is supported, the IIO device provides different sysfs
interfaces to allow using the adjusting the sample rate. Document SPI
offload support for AD4000 and similar devices.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Link: https://patch.msgid.link/eb94013b1a4d66a8492cf094aef3e4410f81d22b.1743110188.git.marcelo.schmitt@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
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Marcelo Schmitt 2025-03-27 18:25:29 -03:00 committed by Jonathan Cameron
parent d66b2c84fb
commit 8c411d4b96
1 changed files with 27 additions and 0 deletions
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Documentation/iio/ad4000.rst
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@ -191,3 +191,30 @@ Typical voltage channel attributes of a differential AD4000 series device:
+-------------------------------------------+------------------------------------------+
| ``in_voltage0-voltage1_scale_available`` | Toggles input span compression |
+-------------------------------------------+------------------------------------------+
SPI offload support
-------------------
To be able to achieve the maximum sample rate, the driver can be used with SPI
offload engines such as the one usually present in `AXI SPI Engine`_, to provide
SPI offload support.
.. _AXI SPI Engine: http://analogdevicesinc.github.io/hdl/projects/pulsar_adc/index.html
To keep up with SPI offloading transfer speeds, the ADC must be connected either
in 3-wire turbo mode or in 3-wire without busy indicator mode and have SPI
controller CS line connected to the CNV pin.
When set for SPI offload support, the IIO device will provide different
interfaces.
* Either ``in_voltage0_sampling_frequency`` or
``in_voltage0-voltage1_sampling_frequency`` file is provided to allow setting
the sample rate.
* IIO trigger device is not provided (no ``trigger`` directory).
* ``timestamp`` channel is not provided.
Also, because the ADC output has a one sample latency (delay) when the device is
wired in "3-wire" mode and only one transfer per sample is done when using SPI
offloading, the first data sample in the buffer is not valid because it contains
the output of an earlier conversion result.