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https://github.com/openbmc/dbus-sensors

D-Bus configurable sensor scanning applications
https://github.com/openbmc/dbus-sensors

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D-Bus configurable sensor scanning applications

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README 

        
# dbus-sensors



dbus-sensors is a collection of sensor applications that provide the

xyz.openbmc_project.Sensor collection of interfaces. They read sensor values

from hwmon, d-bus, or direct driver access to provide readings. Some advance

non-sensor features such as fan presence, pwm control, and automatic cpu

detection (x86) are also supported.



## key features



- runtime re-configurable from d-bus (entity-manager or the like)



- isolated: each sensor type is isolated into its own daemon, so a bug in one

  sensor is unlikely to affect another, and single sensor modifications are

  possible



- async single-threaded: uses sdbusplus/asio bindings



- multiple data inputs: hwmon, d-bus, direct driver access



## dbus interfaces



A typical dbus-sensors object support the following dbus interfaces:



```text

Path        /xyz/openbmc_project/sensors//



Interfaces  xyz.openbmc_project.Sensor.Value

            xyz.openbmc_project.Sensor.Threshold.Critical

            xyz.openbmc_project.Sensor.Threshold.Warning

            xyz.openbmc_project.State.Decorator.Availability

            xyz.openbmc_project.State.Decorator.OperationalStatus

            xyz.openbmc_project.Association.Definitions



```



Sensor interfaces collection are described

[here](https://github.com/openbmc/phosphor-dbus-interfaces/tree/master/yaml/xyz/openbmc_project/Sensor).



Consumer examples of these interfaces are

[Redfish](https://github.com/openbmc/bmcweb/blob/master/redfish-core/lib/sensors.hpp),

[Phosphor-Pid-Control](https://github.com/openbmc/phosphor-pid-control),

[IPMI SDR](https://github.com/openbmc/phosphor-host-ipmid/blob/master/dbus-sdr/sensorcommands.cpp).



## Reactor



dbus-sensor daemons are [reactors](https://github.com/openbmc/entity-manager)

that dynamically create and update sensors configuration when system

configuration gets updated.



Using asio timers and async calls, dbus-sensor daemons read sensor values and

check thresholds periodically. PropertiesChanged signals will be broadcasted for

other services to consume when value or threshold status change. OperationStatus

is set to false if the sensor is determined to be faulty.



A simple sensor example can be found

[here](https://github.com/openbmc/entity-manager/blob/master/docs/my_first_sensors.md).



## configuration



Sensor devices are described using Exposes records in configuration file. Name

and Type fields are required. Different sensor types have different fields.

Refer to entity manager

[schema](https://github.com/openbmc/entity-manager/blob/master/schemas/legacy.json)

for complete list.



## sensor documentation



- [ExternalSensor](https://github.com/openbmc/docs/blob/master/designs/external-sensor.md)

  virtual sensor



## Sensor Type Documentation



### ADC Sensors



ADC sensors are sensors based on an Analog to Digital Converter. They are read

via the Linux kernel Industrial I/O subsystem (IIO).



One of the more common use cases within OpenBMC is for reading these sensors

from the ADC on the Aspeed ASTXX cards.



To utilize ADC sensors feature within OpenBMC you must first define and enable

it within the kernel device tree.



When using a common OpenBMC device like the AST2600 you will find a "adc0" and

"adc1" section in the aspeed-g6.dtsi file. These are disabled by default so in

your system-specific dts you would enable and configure what you want with

something like this:



```text

iio-hwmon {

    compatible = "iio-hwmon";

    io-channels = <&adc0 0>;

    ...

}



&adc0 {

    status = "okay";

    ...

};



&adc1 {

    status = "okay";

    ...

};

```



**Note** that this is not meant to be an exhaustive list on the nuances of

configuring a device tree but really to point users in the general direction.



You will then create an entity-manager configuration file that is of type "ADC"

A very simple example would like look this:



```text

            "Index": 0,

            "Name": "P12V",

            "PowerState": "Always",

            "ScaleFactor": 1.0,

            "Type": "ADC"

```



When your system is booted, a "in0_input" file will be created within the hwmon

subsystem (/sys/class/hwmon/hwmonX). The adcsensor application will scan d-bus

for any ADC entity-manager objects, look up their "Index" value, and try to

match that with the hwmon inY_input files. When it finds a match it will create

a d-bus sensor under the xyz.openbmc_project.ADCSensor service. The sensor will

be periodically updated based on readings from the hwmon file.