On Mon Jul 12, 2021 at 12:11 PM EDT, Rob Herring wrote: > On Tue, Jul 06, 2021 at 12:09:42PM -0400, Liam Beguin wrote: > > From: Liam Beguin <lvb@xxxxxxxxxx> > > > > An ADC is often used to measure other quantities indirectly. > > This binding describe one case, the measurement of a temperature > > through a temperature transducer (either voltage or current). > > > > Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx> > > --- > > .../iio/afe/temperature-transducer.yaml | 111 ++++++++++++++++++ > > 1 file changed, 111 insertions(+) > > create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > > > > diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > > new file mode 100644 > > index 000000000000..b5a4fbfe75e4 > > --- /dev/null > > +++ b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > > @@ -0,0 +1,111 @@ > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > > +%YAML 1.2 > > +--- > > +$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml# > > +$schema: http://devicetree.org/meta-schemas/core.yaml# > > + > > +title: Temperature Transducer > > + > > +maintainers: > > + - Liam Beguin <lvb@xxxxxxxxxx> > > + > > +description: | > > + A temperature transducer is a device that converts a thermal quantity > > + into any other physical quantity. This binding applies to temperature to > > + voltage (like the LTC2997), and temperature to current (like the AD590) > > + linear transducers. > > + In both cases these are assumed to be connected to a voltage ADC. > > + > > + When an io-channel measures the output voltage of a temperature analog front > > + end such as a temperature transducer, the interesting measurement is almost > > + always the corresponding temperature, not the voltage output. This binding > > + describes such a circuit. > > + > > + The general transfer function here is (using SI units) > > + V(T) = Rsense * Isense(T) > > + T = (Isense(T) / alpha) + offset > > + T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha) > > + > > + When using a temperature to voltage transducer, Rsense is set to 1. > > + > > + The following circuits show a temperature to current and a temperature to > > + voltage transducer that can be used with this binding. > > + > > + VCC > > + ----- > > + | > > + +---+---+ > > + | AD590 | VCC > > + +---+---+ ----- > > + | | > > + V proportional to T +----+----+ > > + | D+ --+ | > > + +---- Vout | LTC2997 +--- Vout > > + | D- --+ | > > + +---+----+ +---------+ > > + | Rsense | | > > + +---+----+ ----- > > + | GND > > + ----- > > + GND > > + > > +properties: > > + compatible: > > + const: temperature-transducer > > + > > + io-channels: > > + maxItems: 1 > > + description: | > > + Channel node of a voltage io-channel. > > + > > + '#io-channel-cells': > > + const: 0 Hi Rob, > > This is a io-channel consumer and producer? > Yes, this is a consumer and a producer. It consumes a single ADC channel and can be fed to something like hwmon. > > + > > + sense-offset-millicelsius: > > + description: | > > + Temperature offset. The default is <0>. > > + This offset is commonly used to convert from Kelvins to degrees Celsius. > > + In that case, sense-offset-millicelsius would be set to <(-273150)>. > > default: 0 > > > + > > + sense-resistor-ohms: > > + description: | > > + The sense resistor. Defaults to <1>. > > + Set sense-resistor-ohms to <1> when using a temperature to voltage > > + transducer. > > default: 1 > > Though why would we set the value to 1 if the default is 1? > I can rephrase this. I meant to say that the default will make this behave like a temperature to voltage transducer. Liam > > + > > + alpha-ppm-per-celsius: > > + description: | > > + Sometimes referred to as output gain, slope, or temperature coefficient. > > + > > + alpha is expressed in parts per million which can be micro-amps per > > + degrees Celsius or micro-volts per degrees Celsius. The is the main > > + characteristic of a temperature transducer and should be stated in the > > + datasheet. > > + > > +additionalProperties: false > > Blank line here. > > > +required: > > + - compatible > > + - io-channels > > + - alpha-ppm-per-celsius > > + > > +examples: > > + - | > > + ad950: temperature-sensor-0 { > > + compatible = "temperature-transducer"; > > + #io-channel-cells = <0>; > > + io-channels = <&temp_adc 3>; > > + > > + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ > > + sense-resistor-ohms = <8060>; > > + alpha-ppm-per-celsius = <1>; /* 1 uA/K */ > > + }; > > + - | > > + znq_tmp: temperature-sensor-1 { > > + compatible = "temperature-transducer"; > > + #io-channel-cells = <0>; > > + io-channels = <&temp_adc 2>; > > + > > + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ > > + alpha-ppm-per-celsius = <4000>; /* 4 mV/K */ > > + }; > > +... > > -- > > 2.30.1.489.g328c10930387 > > > >
