• Peter Meerwald's avatar
    iio: Add INT_TIME (integration time) channel info attribute · 899d90bd
    Peter Meerwald authored
    Integration time is in seconds; it controls the measurement
    time and influences the gain of a sensor.
    
    There are two typical ways that scaling is implemented in a device:
    1) input amplifier,
    2) reference to the ADC is changed.
    These both result in the accuracy of the ADC varying (by applying its
    sampling over a more relevant range).
    
    Integration time is a way of dealing with noise inherent in the analog
    sensor itself.  In the case of a light sensor, a mixture of photon noise
    and device specific noise.  Photon noise is dealt with by either improving
    the efficiency of the sensor, (more photons actually captured) which is not
    easily varied dynamically, or by integrating the measurement over a longer
    time period.  Note that this can also be thought of as an averaging of a
    number of individual samples and is infact sometimes implemented this way.
    Altering integration time implies that the duration of a measurement changes,
    a fact the device's user may be interested in.
    
    Hence it makes sense to distinguish between integration time and simple
    scale. In some devices both types of control are present and whilst they
    will have similar effects on the amplitude of the reading, their effect
    on the noise of the measurements will differ considerably.
    
    Used by adjd_s311, tsl4531, tcs3472
    The following drivers have similar controls (and could be adapted):
    * tsl2563 (integration time is controlled via CALIBSCALE among other things)
    * tsl2583 (has integration_time device_attr, but driver doesn't use channels yet)
    * tsl2x7x (has integration_time attr)
    Signed-off-by: default avatarPeter Meerwald <pmeerw@pmeerw.net>
    Cc: Jon Brenner <jon.brenner@ams.com>
    Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
    899d90bd
sysfs-bus-iio 37.3 KB