linux-kernel - Re: [PATCH] iio: light: as73211: Increase measurement timeout

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Date:   Sun, 13 Sep 2020 10:39:30 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Christian Eggers <ceggers@...i.de>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: light: as73211: Increase measurement timeout

On Wed, 9 Sep 2020 20:04:24 +0200
Christian Eggers <ceggers@...i.de> wrote:

> On Wednesday, 9 September 2020, 18:58:39 CEST, Andy Shevchenko wrote:
> > On Wed, Sep 9, 2020 at 6:45 PM Christian Eggers <ceggers@...i.de> 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.
Applied to the togreg branch of iio.git and added a fixes tag to the patch
that introduced the driver.  Note, please try to provide me with one of those
even if the patch hasn't yet gotten into mainline.  It makes life a little
easier for the stable maintainers etc.  I don't always remember to add one
at point of applying the patch.

Thanks,

Jonathan

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