On 11/7/24 10:13 AM, David Lechner wrote: > On 11/7/24 4:51 AM, Miclaus, Antoniu wrote: >>> I'm pretty sure that calibscale and calibbias also need to take into >>> account if resolution boost is enabled or not. >> >> Can you please detail a bit on this topic? I am not sure what I should do. >> > > We haven't implemented oversampling yet in ad4695 yet, so I don't know > exactly what we need to do either. ;-) > > But this is how I would test it to see if it is working correctly or > not. We will need to test this with a 20-bit chip since that is the > only one that will change the _scale attribute when oversampling is > enabled. > > First, with oversampling disabled (_oversampling_ratio = 1), generate > a constant voltage of 1V for the input. Read the _raw attribute. Let's > call this value raw0. Read the _scale attribute, call it scale0 and > the _offset attribute, call it offset0. > > Then we should have (raw0 + offset0) * scale0 = 1000 mV (+/- some > noise). > > Then change the offset calibrate to 100 mV. To do this, we reverse > the calculation 100 mV / scale0 = calibbias (raw units). Write the > raw value to the _calibbias attribute. Then read the _raw > attribute again, call it raw0_with_calibbias. > > This time, we should have (raw0_with_calibbias + offset0) * scale0 > = 1100 mV (+/- some noise). > > Then set _calibbias back to 0 and repeat the above by setting the > _calibscale attribute to 0.90909 (this is 1 / 1.1, which should Now that I have written this, this has me second-guessing if I implemented calibscale correctly on ad4695. It would seem more logical that if we have an actual input voltage of 1 V and a calibscale of 1.1, then the resulting processed value we read should be 1100 mV. Jonathan, can you set me straight? The sysfs ABI docs aren't clear on this point. > add 10% to the measured raw value). Read, the _raw attribute again, > call it raw0_with_caliscale. > > This time, we should have (raw0_with_caliscale + offset0) * scale0 > = 1100 mV (+/- some noise). > > Set _calibscale back to 0. Then set _oversampling_ratio to 2. Read > _scale and _offset again, call these scale1 and offset1. > > Then repeat the steps above using scale1 and offset1 in the > calculations. The raw values will be different but the resulting > processed values (mV) should all be the same if the attributes > are implemented correctly. >
