On Tue, 13 Jun 2023 12:37:39 +0200 David Schiller <david.schiller@xxxxxx> wrote: > On Wed, 2023-06-07 at 15:52 +0100, Jonathan Cameron wrote: > > Not 'official' though it is fairly commonly used, but the documented > > ABI in > > Documentation/ABI/testing/sysfs-bus-iio* > > is and these aren't there either. > > > > I'm not 100% sure this is the right way to solve this ABI gap though > > so need to have a bit of a think about it. Using a modifier means we > > can't > > use them for anything else, so need to consider if there are other > > modifiers > > (or it has meaning for differential channels) when deciding if this is > > an ABI we want to add. > > The naming of the modifiers is also somewhat confusing. The HW registers > represent the DFT of the input signal, which together with a gain factor > is used to calculate the impedance. Dimensionally the quantities are > admittances. "voltage_real" and "voltage_imag" are therefore not quite > fitting. In that case, sounds like we need a new channel type to correctly reflect that they are admittance rather than pretending they are voltages. > > Also the sweep setup commands are only run once per buffer (in > ad5933_ring_preenable). This means a buffer can only be used for one > sweep and then has to be disabled and enabled again. As the driver does > not implement any triggers this is right now the only way to start a > measurement. This sounds a bit like the impact sensors - where an event triggers a series of measurements of 'something'. > > Do you think it would make sense to implement a user-space trigger to > start a measurement sweep? This would mean that a buffer can be reused. > Right now the "iio_readdev" test program from libiio does not work due > to this behavior. I don't know how this is handled on other IIO drivers. A single trigger normally results in the capture of a single set of channels measurements. Here that's sort of the case, but the set of channels is huge - because each one corresponds to a particular frequency. There can I think be up to 512 such points. It would be messy to represent so many channels (if nothing else some of the ways we store data in IIO - particularly events, are limited to 256 channels). My guess is that the calculations around a sweep are sufficiently complex that, if libiio handled the re setup of a sweep neatly, it would be fine to go through the disable / reenable of the buffer? I think bodging in trigger support where a trigger causes 'N' samples would be tricky. There is another option though I'm not sure how closely it fits. A channel can have a scan_type element of repeats which could be set to a fixed value of 512 (likely all scan_type things it's not runtime configurable) as this might be considered to be lots of repeated reads of a single channel. > > Lastly, should I CC the original author (Michael Hennerich) going > forward? Sure - +CC Michael. > > Thanks! > >
