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Reviewed-by: David Lechner Signed-off-by: Marcelo Schmitt --- Documentation/iio/ad4030.rst | 39 ++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/Documentation/iio/ad4030.rst b/Documentation/iio/ad4030.rst index b57424b650a8..9caafa4148b0 100644 --- a/Documentation/iio/ad4030.rst +++ b/Documentation/iio/ad4030.rst @@ -92,6 +92,45 @@ Interleaved mode In this mode, both channels conversion results are bit interleaved one SDO line. As such the wiring is the same as `One lane mode`_. +SPI offload wiring +^^^^^^^^^^^^^^^^^^ + +.. code-block:: + + +-------------+ +-------------+ + | CNV |<-----+--| GPIO | + | | +--| PWM0 | + | | | | + | | +--| PWM1 | + | | | +-------------+ + | | +->| TRIGGER | + | CS |<--------| CS | + | | | | + | ADC | | SPI | + | | | | + | SDI |<--------| SDO | + | SDO |-------->| SDI | + | SCLK |<--------| SCLK | + +-------------+ +-------------+ + +In this mode, both the ``cnv-gpios`` and a ``pwms`` properties are required. +The ``pwms`` property specifies the PWM that is connected to the ADC CNV pin. +The SPI offload will have a ``trigger-sources`` property to indicate the SPI +offload (PWM) trigger source. For AD4030 and similar ADCs, there are two +possible data transfer zones for sample N. One of them (zone 1) starts after the +data conversion for sample N is complete while the other one (zone 2) starts 9.8 +nanoseconds after the rising edge of CNV for sample N + 1. + +The configuration depicted in the above diagram is intended to perform data +transfer in zone 2. To achieve high sample rates while meeting ADC timing +requirements, an offset is added between the rising edges of PWM0 and PWM1 to +delay the SPI transfer until 9.8 nanoseconds after CNV rising edge. This +requires a specialized PWM controller that can provide such an offset. +The `AD4630-FMC HDL project`_, for example, can be configured to sample AD4030 +data during zone 2 data read window. + +.. _AD4630-FMC HDL project: https://analogdevicesinc.github.io/hdl/projects/ad4630_fmc/index.html + SPI Clock mode -------------- -- 2.39.2