Intel SE7525GP2 Product Specification - Page 110

Platform Management Intel® Server Boards SE7320SP2 and SE7525GP2 5.1.3 IPMI Sensor Model An IPMI-compatible sensor model is used to unify the way that temperature, voltage, and other platform management status and control is represented and accessed. The implementation of this model is done according to command and data formats defined in the Intelligent Platform Management Interface Specification. Most of the monitored platform elements are accessed as logical sensors under this model. This access is accomplished using an abstracted, message-based interface (IPMI messages). Instead of having system software access the platform monitoring and control hardware registers directly, it sends commands, such as the Get Sensor Reading command, for sensor access. The message-based interface isolates software from the hardware implementation. System management software discovers the platform's sensor capabilities by reading the sensor data records from a sensor data record repository managed by the management controller. Sensor data records provide a list of the sensors, their characteristics, location, type, and associated sensor number, for sensors in a particular system. The sensor data records also hold default threshold values (if the sensor has threshold based events), factors for converting a sensor reading into the appropriate units (mV, rpm, degrees Celsius, etc.), and information on the types of events that a sensor can generate. Sensor data records also provide information on where field replaceable unit (FRU) information is located, and information to link sensors with the entity and/or FRU they are associated with. Information in the SDRs is also used for configuring and restoring sensor thresholds and event generation whenever the system powers up or is reset. This is accomplished via a process called the 'initialization agent'. The mBMC reads the SDRs and based on bit settings, writes the threshold data. Then it enables event generation for the various sensors it monitors and in management controllers on the IPMB for systems based on the management models. System management software uses the data contained in the sensor data record information to locate sensors in order to poll them, interpret, and present their data readings, adjust thresholds, interpret SEL entries, and alter event generation settings. 5.1.4 Private Management Buses A private management bus is a single-master I2C bus that is controlled by the management controller. Access to any of the devices on the private management bus is accomplished indirectly via commands to the management controller via the IPMB or system interfaces. Private Management busses are a common mechanism used for accessing temperature sensors, system processor information, and other server board monitoring devices that are located in various locations in the system. The devices on the private management bus are isolated from traffic on the IPMB. Since devices such as temperature sensors are polled by the management controller, this gets the polling traffic off the public IPMB bus. This also increases the reliability of access to the information, since issues with IPMB bus arbitration and message retries are avoided. Placing managed I2C devices on the private management bus frees the I2C addresses that those devices would have used on the IPMB. 98 Revision 4.0