From 899d90bdf4d4ef4c3ac0b33cd337c9b3e999ec2d Mon Sep 17 00:00:00 2001 From: Peter Meerwald Date: Sun, 8 Sep 2013 16:20:00 +0100 Subject: iio: Add INT_TIME (integration time) channel info attribute 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: Peter Meerwald Cc: Jon Brenner Signed-off-by: Jonathan Cameron --- include/linux/iio/sysfs.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/linux/iio/sysfs.h') diff --git a/include/linux/iio/sysfs.h b/include/linux/iio/sysfs.h index 2958c960003a..8a1d18640ab9 100644 --- a/include/linux/iio/sysfs.h +++ b/include/linux/iio/sysfs.h @@ -100,6 +100,21 @@ struct iio_const_attr { #define IIO_CONST_ATTR_SAMP_FREQ_AVAIL(_string) \ IIO_CONST_ATTR(sampling_frequency_available, _string) +/** + * IIO_DEV_ATTR_INT_TIME_AVAIL - list available integration times + * @_show: output method for the attribute + **/ +#define IIO_DEV_ATTR_INT_TIME_AVAIL(_show) \ + IIO_DEVICE_ATTR(integration_time_available, S_IRUGO, _show, NULL, 0) +/** + * IIO_CONST_ATTR_INT_TIME_AVAIL - list available integration times + * @_string: frequency string for the attribute + * + * Constant version + **/ +#define IIO_CONST_ATTR_INT_TIME_AVAIL(_string) \ + IIO_CONST_ATTR(integration_time_available, _string) + #define IIO_DEV_ATTR_TEMP_RAW(_show) \ IIO_DEVICE_ATTR(in_temp_raw, S_IRUGO, _show, NULL, 0) -- cgit v1.2.3