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Sensor monitor something about an object. IPMI defines many types of sensors, but groups them into two main categories: Threshold and discrete. Threshold sensors are “analog”, they have continuous (or mostly continuous) readings. Things like fans speed, voltage, or temperature.

Discrete sensors have a set of binary readings that may each be independently zero or one. In some sensors, these may be independent. For instance, a power supply may have both an external power failure and a predictive failure at the same time. In other cases they may be mutually exclusive. For instance, each bit may represent the initialization state of a piece of software.


Controls are not part of the IPMI spec, but are necessary items in almost all systems. They are provided as part of OpenIPMI so that OEM code has a consistent way to represent these, and so OpenIPMI is ready when the IPMI team finally sees the light and adds controls. OpenIPMI defines many types of control: lights, relays, displays, alarms, reset, one-shot-reset, power, fan speed, general outputs, one-shot outputs, and identifiers.

For all controls except displays and identifiers, the control may actually control more than one device. With some controls, multiple device may be controlled together and individual ones cannot be set (ie, the same message sets all of them). For these types of controls, OpenIPMI represents them as a single control with multiple devices. All the devices are read and set at once.

Reset controls are reset settings that can be turned on and off. One-shot-reset controls cause a reset by setting the value to 1; they are not readable and setting them to zero returns an error.

Lights are on/off colored devices, like an LED. They may be multi-color, but can only show one color at a time. For instance, if you work for Kmart, or you are managing a CompactPCI system with hot-swap, you will have a blue light in your system. You can search through the controls to find a light that’s blue. Then, if a special is on, or you want the operator to remove a card, you can light the blue light. Lights may blink, too. Two types of lights are available. Transition lights can have a series of transitions; as series of transition is called a value. Each value describes a sequence of one or more transitions the light may go through. Setting lights allow direct setting of the color and on/off time of the light.

Relays are binary outputs. Most telephony systems have them; they are required by telephony specs. They are simple on/off devices.

Displays are two-dimensional arrays of characters. OpenIPMI allows you to change individual characters at will.

Alarms are bells, whistles, gongs, or anything to alert the user that something is wrong. Reset controls are used to reset the entity to which they are attached. Power controls can be used to control power to or from an entity. A power control on a power supply would generally control output power. A power control on a board would generally control input power to the board.

Fan speed controls can be used to set the speed of a fan. General outputs are outputs that don’t fall into one of the previous categories. One-shot outputs are like general outputs, but perform some action when set to one and are not readable. Setting them to zero returns an error.

Identifier controls hold identification information for a system, such as a chassis id, chassis type, geo- graphic address, or whatever.

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