On 26/05/17 03:58PM, Jonathan Cameron wrote: > On Fri, 08 May 2026 18:00:25 +0100 > Rodrigo Alencar via B4 Relay <[email protected]> > wrote: > > > From: Rodrigo Alencar <[email protected]> > > > > Add custom ABI documentation file for the DDS AD9910 with sysfs entries to > > control Parallel Port, Digital Ramp Generator and OSK parameters. > > > > Signed-off-by: Rodrigo Alencar <[email protected]> > I'm fine with phase and frequency as defined, but for the scaling it made me > wonder. > For outvoltage0 channels the assumption the value is the peak voltage so if > we know what input to be modulated by the ramp generator can we express them > in volts (well milivolts) rather than as a scaling multiplier?
The DAC output is current-based and differential. Voltage conversion would happen outside the device... using a resistor load or an op-amp transimpedance stage, and I am no expert on that, but that often requires impedance matching so voltage levels may depend on the frequency. Then, I suppose that voltage is not the right unit to use. The scale here controls the amplitude of the varying signal. Assuming the peak voltage (amplitude) is constant means we have a constant envelope, but that should not mean we can't control it or it should not mean that the hardware can have other ways to control it. That said, scale behaves as a "gain multiplier". > > That seems to me like it fits better with the overall ABI. > > > +What: > > /sys/bus/iio/devices/iio:deviceX/out_altvoltageY_scale_offset > > +KernelVersion: > > +Contact: [email protected] > > +Description: > > + For a channel that allows amplitude control through buffers, > > this > > + represents the value for a base amplitude scale. The actual > > output > > + amplitude scale is a result with the sum of this value. > > + > > > + > > +What: > > /sys/bus/iio/devices/iio:deviceX/out_altvoltageY_scale_roc > > Silly question perhaps but can work out how this related to millivolts/sec > That might make a more intuitive interface than scaling multiplier per sec > Perhaps the combination with offset makes this impossible though maybe that > could be a expressed as a voltage offset? Afterall if the amplitude being > scaled is 5V then 5 * (offset + scale) = 5 * offset + 5 * scale > > > +KernelVersion: > > +Contact: [email protected] > > +Description: > > + Amplitude scale rate of change in 1/s for channels that ramp > > + amplitude. This value may be influenced by the channel's > > + sampling_frequency setting. > > -- Kind regards, Rodrigo Alencar
