On Tue, 14 Jan 2025 16:26:16 +0200 Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote: > On 14/01/2025 15:02, Javier Carrasco wrote: > > On Tue Jan 14, 2025 at 7:43 AM CET, Matti Vaittinen wrote: > > ... > >>> I will give you a simple example, so you can tell me where my reasoning > >>> fails: > >>> > >>> raw = 100 counts > >>> scale = 2.1504 lux/count (when IT=25ms and GAIN=1/8) > >>> processed = 215.04 lux (raw * scale, ABI compliant for IIO_LIGHT) > >> > >> Your reasoning does not fail. But, the scale = 1 / (N * total_gain), > >> right? (N here depends on how we choose the scale/gain values) Here, > >> the total_gain means the effect of both the hardware_gain and the > >> integration time. > >> > >> Hence, > >> processed = X * (raw * scale) > >> > >> => processed = X * (raw * (1 / (N * total_gain)) > >> => processed = X * raw / (N * total_gain); > >> > >> Hence I thought you might be able to get rid of this 64bit division by > >> using the total_gain from the iio_gts_get_total_gain() instead of > >> using the scale. Or, am I missing something? > >> > > > > I am not sure by X you mean the maximum resolution, but if that is the > > case, the following would work (pseudo-code): > > Yes. X denoted the value by which the count needs to be multiplied to > get the lux (when total gain "in the terms of gts" is x1. I think in > this particular case the "gain is x1" is a bit confusing as it appears > this really means the hardware gain is 1/8, right?). Anyways, lux/count > it is, so in short - yes. :) > > > > > /* Maximum resolution (2.1504 lux/count) * 10000 */ > > #define VEML6030_MAX_RES 21504 > > > > total_gain = iio_gts_get_total_gain(); > > processed_int = raw * VEML6030_MAX_RES / total_gain / 10000; > > Yes. This is what I was thinking of. > > > processed_micro = ((raw * VEML6030_MAX_RES / total_gain) % 10000) * 100; > > gah. I didn't consider representing the micro portion. Staring this > makes me feel dizzy :) Well, it looks correct, and I guess the precision > is not lost by the division(?) But yes, you did perfectly get what I was > after! > > Jonathan, do you think I am just guiding Javier to make a mess? :) This is an area you've thought about a lot more than me. Whether it is worth avoiding the 64 bit maths is an interesting question and I guess depends where this part is typically showing up. Jonathan > > If not, then this might be the way to go. > > Yours, > -- Matti
