Document SPI offload support for the ad7380 driver. Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx> --- Documentation/iio/ad7380.rst | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/Documentation/iio/ad7380.rst b/Documentation/iio/ad7380.rst index cff688bcc2d9601a9faf42d5e9c217486639ca66..12709ce051110e68b6f0c9b9a0baefcc954f2bc0 100644 --- a/Documentation/iio/ad7380.rst +++ b/Documentation/iio/ad7380.rst @@ -169,6 +169,42 @@ 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. + +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/ad738x_fmc/index.html + +When SPI offload is being used, some attributes will be different. + +* ``in_voltage-voltage_sampling_frequency`` attribute is added for setting the + sample rate. +* ``in_voltage-voltage_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 ``buffer0/in_voltage0-voltage1_type`` and the + ``buffer0/in_voltage2-voltage3_type`` attributes. + +Effective sample rate for buffered reads +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Using SPI offload, the PWM generator drives the starting of the conversion by +executing the pre-recorded SPI transfer at each PWM cycle, asserting CS and +reading the previous available sample values for all channels. +Default sample rate is set to a quite low frequency, to allow oversampling x32, +user is then responsible to adjust ``in_voltage-voltage_sampling_frequency`` for +the specific case. + +For single-ended chips where 2 banks of simultaneous inputs are available, as +ad7386, ad7387 and ad7388, if at least one channel from each bank is enabled in +a buffered read, the effective sample rate will be 1/2 of what is set as +``in_voltage-voltage_sampling_frequency``, this because a separate conversion +needs to be done for each bank. + Unimplemented features ---------------------- -- 2.48.1
