On Tue, Mar 4, 2025 at 10:39 AM Angelo Dureghello <adureghello@xxxxxxxxxxxx> wrote: > > Document SPI offload support for the ad7380 driver. > > Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx> > --- > Documentation/iio/ad7380.rst | 54 +++++++++++++++++++++++++++++++++++--------- > 1 file changed, 43 insertions(+), 11 deletions(-) > > diff --git a/Documentation/iio/ad7380.rst b/Documentation/iio/ad7380.rst > index cff688bcc2d9601a9faf42d5e9c217486639ca66..e593ab6037b0da4cebfad148313f21cca7f00fd4 100644 > --- a/Documentation/iio/ad7380.rst > +++ b/Documentation/iio/ad7380.rst > @@ -142,21 +142,21 @@ Example for AD7386/7/8 (2 channels parts): > .. code-block:: > > IIO | AD7386/7/8 > - | +---------------------------- > - | | _____ ______ > - | | | | | | > + | +---------------------------- > + | | _____ ______ > + | | | | | | > voltage0 | AinA0 --|--->| | | | > - | | | mux |----->| ADCA |--- > + | | | mux |----->| ADCA |--- > voltage2 | AinA1 --|--->| | | | > - | | |_____| |_____ | > - | | _____ ______ > - | | | | | | > + | | |_____| |_____ | > + | | _____ ______ > + | | | | | | > voltage1 | AinB0 --|--->| | | | > - | | | mux |----->| ADCB |--- > + | | | mux |----->| ADCB |--- > voltage3 | AinB1 --|--->| | | | > - | | |_____| |______| > - | | > - | +---------------------------- > + | | |_____| |______| > + | | > + | +---------------------------- > It looks like this is just cleaning up whitespace, so should be in a separate patch. > > When enabling sequencer mode, the effective sampling rate is divided by two. > @@ -169,6 +169,38 @@ 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. > + > +.. seealso:: `SPI offload support`_ This is referring to the same section, so doesn't make sense here. > + > +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 reponsible to adjust ``in_voltage-voltage_sampling_frequency`` for s/reponsible/responsible/ > +the specific case. Another important thing to mention here is that for single-ended chips where we have 2 banks of simultaneous inputs, if at least one channel from each bank is enabled in a buffered read, the effective sample rate will be 1/2 of what ``in_voltage-voltage_sampling_frequency`` says because a separate conversion needs to be done for each bank. > + > Unimplemented features > ---------------------- > > > -- > 2.48.1 >
