Over the past five years, CompactPCI has gained wide acceptance as the architecture of choice for equipment manufacturers developing high-availability embedded systems. Its powerful, standards-based computing solutions, hot-swap functionality and high-availability capabilities make it ideal for applications such as communication. AdvancedTCA (ATCA) is also emerging as a standards-based solution in the communications market. For both form-factors, intelligent power management and the power distribution architecture are critical to the success of high service availability for the complete system. System designers considering the use of advanced managed platforms in their applications must consider several power architecture issues.

Intelligent Power Management

CompactPCI power supplies can be fickle components in high-availability systems. Since today’s embedded systems demand higher performance and compute power, power supplies have been stepped up to deliver twice as much power as they did just a few years ago. However, they must deliver that increased power within the same form-factor. These denser power supplies require ample cooling and management, hence the need for intelligent power management.

In the past, power supplies offered simple management information. The two most typical management signals are the Degrade signal, which provides warning when power supply temperature is within 20°C of derating point, and the Power Fail signal, which indicates any output below 90% and/or a low input <36 VDC.

Recently, power supplies have begun implementing the industry standard Intelligent Platform Management Interface (IPMI). IPMI offers a comprehensive set of information to fully manage and predict failures for each power supply. It allows subcomponents from multiple vendors to be monitored by a system’s single shelf manager or redundant shelf managers.

The Intelligent Platform Management Bus (IPMB) is a logical bus that was specified to use the I2C control bus as the physical interface. Power supplies implementing IPMI contain a satellite IPMI/(IPMB) controller. This controller provides an interface to sensors and attaches to the IPMB/I2C bus as the physical interface.

It processes IPMI commands communicated via the IPMB bus protocol. IPMI is a request-response protocol: the shelf manager, also considered the master or baseboard management controller, issues a request message to an intelligent power supply, also considered the slave or satellite management controller. The supply then responds with a separate response message. Request messages and response messages are transmitted on the bus using I2C master write transfers. The sensor data record (SDR) is the sensor information stored on the power supply.

Many shelf management modules provide an in-band and/or out-of-band Ethernet interface so that the shelf can be remotely accessed with a common interface by operations, administration and maintenance (OA&M) managers. The shelf manager then communicates to all intelligent components via IPMI.

A power supply that supports IPMI provides five distinct classes of commands (Figure 1). The main commands are: (1) application commands, (2) sensor/event commands, (3) field replaceable unit (FRU) commands, (4) firmware commands and (5) OEM commands.

Application commands initiate operation with the controller, including controller resets and enabling self-tests. The device ID field allows controller-specific software to identify the unique functionality provided by a particular controller. Since multiple power supplies with the same device ID can operate in a system, power supplies can be standardized, yet, at the same time, maintain different geographic locations and FRU information. The Cold Reset command makes the controller reset, while the Warm Reset command makes it start at the beginning of the program, causing the initialization and startup function to be executed.

Sensor/event commands provide the information read from the power supply’s sensor data record. Typical SDR information for a power supply includes temperature, voltage and current. The Set Sensor Threshold command lets the user establish different threshold levels for each sensor: minor, major and critical. Each threshold on each sensor can be enabled to generate event messages if that threshold is crossed. For controllers that support the generation of event messages, the Set Event Receiver and Get Event Receiver commands must be implemented. When a significant event occurs, such as a power supply failure, that event must be communicated to the shelf manager as soon as possible, rather than the shelf manager being required to wait to respond to a command. In this case, an event message is initiated by the satellite controller.