Intelligent Platform Management Interface (IPMI) explained
The I2C bus is used for system management functions in larger systems. Hot-swap bus buffers may be used to buffer higher capacitances and to provide hot swap capability. One system management architecture is the Intelligent Platform Management Interface (IPMI), an Intel initiative in conjunction with HP, NEC, and Dell for server applications. It consists of three specifications:
IPMI software extensions provide a self-monitoring capability that increases the reliability of the system and monitors the platform physical health characteristics such as: temperatures, voltages, fans, and chassis intrusion. The extensions provide general system management functions such as: automatic alerting, automatic system shutdown and re-start, remote re-start, and power control.
IPMB provide intra-chassis (dark green line inside the box in the figure below) connections using I2C/SMBus as the physical means to transfer information.
ICMB provides inter-chassis (light green line outside the box in the figure below) connections using various different means like RS-485, CAN, or I2C to transfer information.
This new standard is needed because, as the complexity of systems increase, MTBF decreases, and there needs to be a way to monitor and control platform components outside of the normal system operation loop so that failures can be detected and corrected to keep the system operating. IPMI uses the proven capabilities of the I2C bus to provide a self-monitoring capability that increases system reliability. IPMI is a standardized bus/protocol for extending management control, monitoring, and event delivery within the chassis.
IPMI is an I2C-based, multi-master capable, simple Request/Response Protocol. It uses IPMI Command sets, supports non-IPMI devices, is physically I2C, but is write only (master capable devices). For IPMI, hot swap is not required since servers can be powered down to insert or remove cards.
IPMI extensions enable the Baseboard Management Controller (BMC) to accept IPMI request messages from other management controllers in the system. This allows non-intelligent devices as well as management controllers on the bus. The BMC serves as a controller to give system software access to the IPMB.
Hot-swappable bus buffers can be used on the various boards that plug into the motherboard in order to isolate the bus capacitance to each board. The Private Management Buses (green lines on boards in figure above) are local I2C buses for communication with the various slave devices (e.g., temperature sensors and EEPROMs) using normal I2C protocols.
See www.intel.com/design/servers/ipmi/ipmi.htm for additional information.
Use of IPMI in PICMG Architectures
The PICMG (PCI Industrial Computer Manufacturers Group) is a consortium of over 600 companies, which collaboratively develops open interconnection specifications for high performance telecommunications and industrial computing platforms. PICMG specifications that use IPMI include PICMG 2.9 for CompactPCI® applications and the recently announced PICMG 3.x for AdvancedTCATM. AdvancedTCA is a new, larger form factor rack mount board for next-generation telecommunications equipment and is based on switched fabric architectures. Dual redundant IPMBs are mandatory. PICMG requires the hot-swap features of hot-swappable bus buffers since telecom/computing equipment can't be powered down to insert or remove cards. Our NXP PCA9511A or the Linear Technology LTC4300A-1 are the devices normally used.
See www.picmg.org for additional information.
Use of IPMI in VME Architectures
The new VME draft standard indirectly calls for IPMI as the system management protocol by using the PICMG 2.9 system management specification with pin configuration changes since the VME backplane connectors are different from CompactPCI and maximum capacitance changes since CompactPCI can have a maximum of 8 slots while VME can have a maximum of 21 slots.
See the VME Draft Standard VITA 38 - 200x, Draft 0.5, 9 May 02 for additional information.
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