Jonathan, et al., Sorry guys - I've been completely snowed under. I have some thoughts but no time to annunciate. What I do have is confidence in all of you to do the right thing. I'll catch up later. Relationships between integration time and gain can be tricky due to other external factors (aperture, glass density, inking, etc.) and need to be balanced accordingly. Throw in some filtering (ie persistence) and offset calibrations and you have a sticky wicket. Fortunately, most of these devices provide the ability to set parameters independently. It's a blessing and it's a curse. I will be immersed in a wicked project for the next several weeks, after which I expect to come back on-line with some really cool devices coming to IIO. BR Jon ________________________________________ From: Jonathan Cameron [jic23@xxxxxxxxxx] Sent: Sunday, September 01, 2013 8:33 PM To: Peter Meerwald Cc: linux-iio@xxxxxxxxxxxxxxx; Jon Brenner; Lars-Peter Clausen Subject: Re: [PATCH 1/2] iio: add INT_TIME (integration time) channel info attribute 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
