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
