Re: [PATCH] iio: light: as73211: Increase measurement timeout

From: Christian Eggers
Date: Wed Sep 09 2020 - 14:05:54 EST

On Wednesday, 9 September 2020, 18:58:39 CEST, Andy Shevchenko wrote:
> On Wed, Sep 9, 2020 at 6:45 PM Christian Eggers <ceggers@xxxxxxx> wrote:
> > We found some sensors which are much slower (20% at room temperature)
> > than nominal. According to the data sheet, up to 27% is possible. Now I
> > add 33% to the nominal time out, hopefully this is enough.
> I'm wondering if this is a function of temperature.
> And if that has an actual thermistor inside...
I haven't designed the hardware, but I guess that clock generation is done
using an RC oscillator which depends on temperature. Temperature measurement
is possible, but I think the recommended way is to externally control the
integration time using the SYN pin and to get the actual number of RC cycles
from a register. But generating the required waveform for the SYN pin using a
uC general purpose timer seems challenging.

I wouldn't be surprised if the measurement results also depend on the exact
value of the supply voltage.