On 08/18/13 22:30, Peter Meerwald wrote: > Hello, > >>> integration time is in seconds; it controls the measurement >>> time and influences the gain of a sensor >>> >>> used by adjd_s311, tsl4531 >>> the following drivers have similar controls: >>> * 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) > >> I know this has come up before (and I'm not actually expressing oposition >> to this going into info_mask) but could you sumarise the arguments for why >> this property cannot be covered by calibscale or scale? >> I'd like to have a little stronger argument for the patch description in Git. > > sounds good; I'd add: > >> 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 it's >> sampling over ta more relevant range). >> >> Integration time is a way of dealing with noise inherent in the analog >> sensor itself. In this case 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 and the user of the device may be interested > >> 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 on the measurements will differ considerably. > > integration time may or may not have an impact on the range of values > measured > > both characteristics cannot be expressed with scale/calibscale in a > satisfying way > > let's see if further comments come up, and I'll repost Not much come out of the wood work so something like what you propose will do nicely! I would also like a short description in the documentation file so we don't have to keep refering people back to the original patch. Jon, you still out there? Not heard anything from you for a while and your input on this sort of thing is always valued! Jonathan > > please note that there is a fix for the adjd_s311 driver posted which you > may want to fast-feed to Greg > > thanks, regards, p. > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
