Re: [PATCH v6 16/16] docs: iio: add documentation for ad9910 driver

On 03/07/26 19:30, Jonathan Cameron wrote:
> On Thu, 18 Jun 2026 14:27:32 +0100
> Rodrigo Alencar via B4 Relay <[email protected]> wrote:
> 
> > From: Rodrigo Alencar <[email protected]>
> > 
> > Add documentation for the AD9910 DDS IIO driver, which describes channels,
> > DDS modes, attributes and ABI usage examples.

...

> > +Digital ramp generator (DRG)
> > +----------------------------
> > +
> > +The DRG produces linear frequency, phase or amplitude sweeps using dedicated
> > +hardware. The active ramp target (destination) is selected by enabling the
> > +corresponding typed channel at channel number 130:
> > +
> > +- ``out_frequency130`` (label ``drg_frequency``) — ramp targets frequency
> > +- ``out_phase130`` (label ``drg_phase``) — ramp targets phase
> > +- ``out_altcurrent130`` (label ``drg_amplitude``) — ramp targets amplitude
> > +
> > +Writing ``en=1`` to one of these channels enables the DRG and switches its
> > +destination. Writing ``en=0`` disables the DRG if the channel is the current
> > +active destination; writing to an already-inactive destination is a no-op.
> > +
> > +Each destination channel also exposes a read-only ``scale`` attribute
> > +reporting the physical quantity per ramp register LSB, which allows converting
> > +raw limit codes to physical values.
> > +
> > +The two ramp channels ``out_altcurrent131`` (``drg_rising``) and
> > +``out_altcurrent132`` (``drg_falling``) configure ascending and descending
> > +ramp parameters independently.
> > +
> > +Destination channel attributes
> > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +
> > +.. flat-table::
> > +   :header-rows: 1
> > +
> > +   * - Attribute
> > +     - Unit
> > +     - Description
> > +
> > +   * - ``en``
> > +     - boolean
> > +     - Enable the DRG with this channel as the active destination. Only one
> > +       destination can be active at a time.
> > +
> > +   * - ``scale``
> > +     - Hz/LSB, rad/LSB or mA/LSB
> > +     - Read-only. Physical quantity per raw units. Multiply a ramp
> > +       rising/falling channel ``raw`` value by this scale to get the physical
> > +       ramp target.
> > +
> > +Ramp channel attributes
> > +^^^^^^^^^^^^^^^^^^^^^^^
> > +
> > +.. flat-table::
> > +   :header-rows: 1
> > +
> > +   * - Attribute
> > +     - Unit
> > +     - Description
> > +
> > +   * - ``dwell_en``
> > +     - boolean
> > +     - Enable dwell at the ramp limit. When disabled, the ramp
> > +       auto-transitions at this limit without waiting for the DRCTL pin.
> > +       Disabling both creates a bidirectional continuous ramp (triangular
> > +       pattern). Other combinations create single-shot ramps at the DRCTL
> > +       pin transition.
> > +
> > +   * - ``raw``
> > +     - integer (64-bit)
> > +     - Ramp limit expressed as a raw DRG register code in
> > +       :math:`[0, 2^{32}-1]`. The physical value is ``raw * scale`` where
> > +       ``scale`` is read from the active destination channel.
> > +
> > +   * - ``sampling_frequency``
> > +     - Hz
> > +     - Ramp clock rate. Controlled by an integer divider; the written value
> > +       is adjusted to the nearest supported rate.
> > +
> > +   * - ``raw_roc``
> > +     - /s
> > +     - Rate of change. Number of register codes advanced per second, computed
> > +       from the hardware step size and the current ramp clock. Writing
> > +       requires ``sampling_frequency`` to be configured first.
> > +
> > +Usage examples
> > +^^^^^^^^^^^^^^
> > +
> > +Configure a frequency sweep from 40 MHz to 60 MHz with a rate of change of
> > +25 GHz/s:
> > +
> > +.. code-block:: bash
> > +
> > +  # Disable dwell on both limits for a bidirectional continuous ramp
> > +  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_dwell_en
> > +  echo 0 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_dwell_en
> > +
> > +  # Set ramp rate at 250 MHz
> > +  echo 250000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_sampling_frequency
> > +  echo 250000000 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_sampling_frequency
> > +
> > +  # read the frequency scale to convert physical values to raw units
> > +  cat /sys/bus/iio/devices/iio\:device0/out_frequency130_scale
> > +  0.232830643650
> > +
> > +  # 40 MHz / 0.232830643650 = 171798692
> > +  echo 171798692 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_raw
> > +  # 60 MHz / 0.232830643650 = 257698038
> > +  echo 257698038 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_raw
> 
> Why is this writing frequencies to altcurrent channels? Shouldn't this be the
> frequency ones?

All the attributes for ramp up/down channels would do the same thing in separate
channel types: sampling_frequency, raw, raw_roc and dwell_en... do we need frequency
and phase ones? For the DRG, right now I have:

* out_frequency130: en, scale
* out_phase130: en, scale
* out_altcurrent130: en: scale
	* out_altcurrent131: raw, raw_roc, dwell_en, sampling_frequency
	* out_altcurrent132: raw, raw_roc, dwell_en, sampling_frequency
 
> > +
> > +  # 25 GHz/s / 0.232830643650 = 107374182402
> > +  echo 107374182402 > /sys/bus/iio/devices/iio\:device0/out_altcurrent131_raw_roc
> > +  echo 107374182402 > /sys/bus/iio/devices/iio\:device0/out_altcurrent132_raw_roc
> > +
> > +  # Enable the DRG with frequency as the destination
> > +  echo 1 > /sys/bus/iio/devices/iio\:device0/out_frequency130_en
> > +

...

-- 
Kind regards,

Rodrigo Alencar