Hi all,there were some sysfs userspace questions on linux-iio where we would like to get some more comments on.
First thing, there are some attributes describing the layout of a ring buffer that can be read out via a char device. The buffer contains several entries with each containing so called scan elements. All entries have the same layout. It is described in a directory scan_elements (see below) that contains three attributes per scan element.
OK, no packed buffers for now, but we should implement variable
> sample sizes for standard types. Indeed we already have this for > the timestamp, which is always 64 bit.
To be compatible with future extensions we could have: |- /sys/bus/iio/device0/buffer0/scan_elements/ |- accel_x_en (0 or 1) |- accel_x_type (i.e. s14/16, see *) |- accel_x_index (position inside the buffer entry) * s14/16 means signed 14 bits, stored in 16 bits, right aligned.
> If it's left aligned we can just modify the scale attribute and > give the 16 bit interpretation in <channel>_raw. Is the 's14/16' self explaining or should we use some other format? Is 'type' a good postfix for the attribute? Next question: how strictly we want to resamble the hwmon ABI? To sum up the discussion: Hwmon has files with the postfix _input to read values scaled to reasonable units for fixed point representation. So the units are sometimes scaled down to 'millis' e.g. millivolt, millidegree Celsius. We agreed that we want to keep this, whenever we use the _input postfix. For IIO there is also the postfix triple _raw, _scale and _offset, where the final value is calculated by (_raw + _offset) * _scale. Floating point values are allowed for any of these files. The question in place was: Do we want to resamble the 'milli' units or should we stick to standard SI units (radians, kelvin, etc.) as floating point math is necessary anyway. Regards, -- Dipl.-Inf. Manuel Stahl Fraunhofer-Institut für Integrierte Schaltungen IIS - Leistungsoptimierte Systeme - Nordostpark 93 Telefon +49 (0)911/58061-6419 90411 Nürnberg Fax +49 (0)911/58061-6398 http://www.iis.fraunhofer.de manuel.stahl@xxxxxxxxxxxxxxxxx
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