Messages in this thread | | | Subject | Re: [PATCH v3 1/2] dt-bindings: iio: afe: add current-sense-shunt and voltage-divider | From | Peter Rosin <> | Date | Mon, 16 Apr 2018 16:00:44 +0200 |
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On 2018-04-10 17:28, Peter Rosin wrote: > +Example: > +The system voltage is circa 12V, but divided down with a 22/200 > +voltage divider to adjust it to the ADC range. > + > +SYSV ADC GND > + + + + > + | .-----. | .----. | > + '--| 200 |-+-| 22 |--' > + '-----' '----' > + > +sysv { > + compatible = "voltage-divider"; > + io-channels = <&maxadc 1>; > + > + /* Multiply the ADC voltage by 222/22 to get the system voltage. */ > + numerator = <222>; /* 200 + 22 */ > + denominator = <22>; > +};
While I already got a reviewed-by from Rob, and maybe I shouldn't be stirring the pot, but I had an umpteenth look and I now think this one looks a bit odd. It shows a bit that it originates from when the compatible was the very generic "io-channel-unit-converter" in v1 of the series. What I mean is that a voltage divider presumable always gets you a lower voltage. Therefore, one would assume that the denominator should be larger than the numerator. The fact that this translates into the inverted fraction when calculating backwards through the voltage divider should probably not affect the binding.
So, in the above example, I think it would make more sense to have
numerator = <22>; denominator = <222>; /* 200 + 22 */
(and then, naturally, adjust the driver to invert the fraction)
Comments?
Cheers, Peter
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