The management of CompactPCI boards has received much attention recently. Although the functionality has existed since early 2000, vendors and users have only just started to explore it's capabilities. Users of CompactPCI have started to look for ways to manage boards using an industry standard management mechanism. The PCI Industrial Computer Manufacturers Group (PICMG) developed PICMG 2.9 CompactPCI System Management Specification to address system management issues in CompactPCI. This article will look at the requirements for system management, how PICMG 2.9 can be used to solve some of the system management challenges as well as areas that need further work.

 System Management Requirements

Early CompactPCI boards had a self contained management architecture. That is, a board was responsible for managing itself. A board would determine if an over temperature condition existed, or if a watchdog event occurred and would take the appropriate action. In these systems, there was no single management entity responsible for managing all of the boards within a system. Early attempts might have used shared memory architecture or PCI based message passing scheme as a way to share management information between boards. As CompactPCI was applied to High Availability applications, the requirements for system management started to grow. In these applications it was no longer good enough to know if a board was operating properly. These applications needed to be able to check the health of all Field Replaceable Units (FRUs), reset FRUs, power FRUs on and off, and monitor the temperature of FRUs. The definition of a FRU was expanded beyond that of a board to include fans, power supplies, backplanes, alarm panels and internal temperature sensors. The ability to identify the revision and serial number of the FRUs in a system was an additional requirement placed on system management. As the demands on system management grew, it became apparent that a dedicated data transport would be required. The system management traffic was too important to mix with data traffic on the PCI bus. The ability to remotely monitor and control the system was also desirable as well as the need to leverage existing standards.

 PICMG 2.9

The PICMG 2.9 specification was created to as a companion to the PICMG 2.0 CompactPCI Core Specification. PICMG 2.9 Revision 1.0 was released February 2000 with a follow on ECR in May 2002. The Core specification defined the pins to be used for system management (IPMB_SCI, IPMB_SDA, IPMB_PWR), but did not define the electrical or protocol requirements for these pins. PICMG 2.0 defines the electrical characteristics, and protocol for system management messages for CompactPCI boards. In architecting a system management solution for CompactPCI the authors looked to other industry standards for existing solutions that could be leveraged. The obvious choice was IPMI (Intelligent Platform Management Interface). The IPMI specification was developed by Intel, Dell, Hewlett-Packard, and NEC in 1998 to provide a standard interface to be used for monitoring a server's physical characteristics such as temperature, voltage, fans, power supplies and chassis. IPMI is comprised of three specifications Intelligent Platform Management Interface, Intelligent Platform Management Bus (IPMB) and Intelligent Chassis Management Bus (ICMB). The IPMI specification defines the interface between management software and chassis management hardware. The IPMB specification defines the internal Intelligent Platform Management Bus. The ICMB specification defines an external bus for connecting additional IPMI enabled systems. By incorporating IPMI into CompactPCI, PICMG is able to leverage work done by the IPMI consortium.

 System Management Physical Link

The electrical interconnect for system management in CompactPCI is based on the inter-IC (I2C) bus. This bus is a two wire serial interface (clock, data) driven by open-collector drivers. Devices arbitrate for the bus based on a collision detection mechanism. Data rate of 100Kb/sec is currently defined and can be extended to 400Kb/sec. The I2C data and clock signals are referred to as an IPMB. The CompactPCI specification defines two IPMBs (IPMB0 and IPMB1). Use of the second IPMB is optional. The IPMB interconnects are located on the CompactPCI J1 and J2 connectors as defined in Table 1.

Table 1 CompactPCI Pin Assignments for IPMB

The system management interface on CompactPCI boards is powered by a dedicated system management power supply (Vsm). This separate supply allows the CompactPCI board's system management controller to be power and operational while the board is powered down. The IPMB can be extended to fans, power supplies and chassis thermal monitors. A typical IPMB backplane interconnect is shown in Figure 1.

Figure 1 IPMB Interconnect

In Figure 1, the System Management Controller has a connection to devices that are external to the backplane but internal to the chassis. An IPMB extension connector is defined in PICMG 2.9 to standardize the interconnect for non-CompactPCI board based IPMB connections. CompactPCI vendors have the option of connecting the IPMB in a bus configuration as shown in Figure 2 or a star configuration. The ability to use IPMB in a bussed environment requires that hot swap capabilities be added to the I2C specification. The IPMB needs to be able to support the insertion and removal of devices while power is applied and data is present. This requirement can be difficult to meet depending on the type of I2C interface used. This is one area where the PICMG 2.9 specification enhances existing standards.

 System Management Commands

The IPMB is used to transport commands between the System Management Controller and the Management Controller on CompactPCI boards. The format and definition of the commands sent over the IPMB is based on the IPMI v1.5 Specification. The IPMI specification was architected around the server motherboard environment. In a typical motherboard, the Management Controller connects to a variety of dumb sensors located on the motherboard and within the chassis. The command set contains commands tailored to this environment and are intended to handle sensors, data repositories, event logs and watchdog timers. Although the IPMI command set may be appropriate for motherboard environments, it is lacking in its ability to provide some data that is independent of the hardware. In May 2002, the PICMG 2.9 specification was enhanced with an Engineering Change Notice that addressed some of the shortcomings in the original 2.9 specification. The ECR was intended to define a hardware independent mechanism for software to determine the capabilities of a backplane and to determine what slot a CompactPCI board was plugged into. On a typical CompactPCI board, the Management Controller might connect to the Geographical Address lines, Hot Swap Switch located in the board's handle, Blue Hot Swap LED, and possibly HEALTHY# and ENUM#. The typical connections to the Management Controller on a CompactPCI Peripheral board and System Management Controller board are shown in Figure 3.

Figure 3 Management Controller Interconnects

One of the challenges not readily apparent is a consistent method that can be used to address the devices on the CompactPCI Peripheral Card. The IPMI addresses sensors by a sensor number. PICMG has yet to standardize the number for various sensors on a board. The resulting challenge is that the System Management Controller has no standard method to access features such as the Blue LED or Hot Swap switch on the board. Some of these shortcomings are expected to be addressed in a future specification currently under development called CompactTCA.

 Remotely Managing CompactPCI Boards

The management structure defined up to this point is intended to manage boards and other FRUs within a chassis. Some applications require the remote monitoring and management of CompactPCI systems. There is a standard for IP encapsulation of IPMI messages. This standard is Remote Management Protocol (RMCP). By using a System Management Controller with an Ethernet interface and support for RMCP, users of CompactPCI systems can remotely monitor and manage CompactPCI systems. The use of RMCP by the CompactPCI community is still in its infancy. It is likely that additional work will need to be done to allow interoperability among the various vendors of CompactPCI systems. This is another area that is likely to be address in CompactTCA

 Summary

The PICMG2.9 specification is intended to provide a management infrastructure and interface that leverages the existing IPMB and IPMI standards. This standard provides a way for users of CompactPCI to control and monitor the status of FRUs within a chassis and is independent of the PCI bus. It is likely that future CompactPCI architectures will rely on PICMG2.9 as the method for controlling Hot Swap as well as the monitoring of a board's health. These capabilities will require that enhancements be made in PICMG 2.9's ability to be more hardware independent. This work is likely to be done in the CompactTCA specification currently under development. Users of CompactPCI can also take advantage of RMCP as a way to manage systems that are remote over IP. The PICMG 2.9 specification is a separate and optional specification. Users requiring the management capabilities of PICMG2.9 will need to ensure that the products purchased comply with the specification. Although the management of CompactPCI boards and systems is in its infancy, standards do exist that will allow interoperability and can solve the management challenges that exist today.