The Advanced Telecommunications Architecture (ATCA) and MicroTCA specifications include hardware platform management capabilities because the target markets demand high reliability and maintainability. The specifications intentionally omit the implementation details of the hardware and firmware for the management devices. This allows the designer to consider all of the trade-offs and decide what is best.

From the external, management-oriented view (Figure 1), a shelf is a collection of field replaceable units (FRUs) and their associated sensors. When you look at the actual FRU designs you will find that they are often intelligent, incorporating a microprocessor or an FPGA with a microprocessor core running shelf manager or Intelligent Platform Management Controller (IPMC) firmware. An FRU can also be non-intelligent, but managed by an intelligent FRU. In either case, the external representation of the intelligent and non-intelligent FRUs and their sensors is the same.

The Intelligent Platform Management Interface (IPMI) architecture, substantially enhanced by the ATCA and MicroTCA specifications, is used as a standardized method of interacting with the FRUs. This architecture defines messages that travel on the Intelligent Platform Management Bus (IPMB), an I2C bus that interconnects the FRUs inside the shelf. Using IPMI abstracts the physical implementation of the FRU. The only requirement is that the FRU implementation must comply with the IPMI behavioral and I2C electrical specifications.

Approaches to Management Solution

ATCA supports both intelligent and non-intelligent FRUs. Non-intelligent FRUs are usually managed by an IPMC on another intelligent FRU or by the shelf manager (the managing controller). The managing controller represents itself and its own sensors (such as temperature or voltage sensors) to the shelf manager, as well as representing its managed FRUs and their sensors. A managing IPMC can represent AdvancedMC (AMC) modules to the shelf manager, using an architecture defined by the AdvancedMC specification.

An IPMC uses IPMI/I2C to communicate with the shelf manager over the IPMB, but the communication interface between the IPMC, its sensors and its managed FRUs is not defined. Each IPMC needs to implement I2C for the IPMB so it is natural to also use I2C-based voltage, current, temperature or presence sensor devices and I2C-based nonvolatile FRU data storage.

The I2C sensor devices that are on an FRU controlled by the IPMC are not directly connected to anything outside of that FRU. The I2C devices on the FRU are accessed in a standardized way via IPMI commands. For the purposes of hardware platform management, the devices in the IPMC are usually exposed as collections of sensors and FRU inventory devices.

For each supported sensor, the IPMC has an associated Sensor Data Record (SDR). IPMI commands are defined to read the contents of the SDR. The SDR contains all information about the sensor: its type, format of the analog reading, measurement units and parameters for conversion from the single-byte “raw” reading to the numeric “processed” reading. The processed reading is expressed in measurement units that make sense to the user like the number of RPMs for a fan tachometer sensor or the number of volts for a voltage sensor. The SDR also contains the human-readable name of the sensor, initial values of thresholds and hysteresis, and, for discrete sensors, the mask of supported states and assertion and deassertion state masks.

So, the IPMC normally represents I2C sensor devices as IPMI sensors, mapping the corresponding I2C device register value to the IPMI analog reading and describing the attributes of the device in the corresponding SDR. I2C devices and signals used as control inputs and outputs are represented as settable sensors. I2C-based EEPROMs are often used to store “FRU information.” The FRU information is a collection of structured records defined by the IPMI or PICMG specifications that describe an FRU and its properties (such as inventory information like serial and model numbers).

A key question for ATCA shelf developers is how to manage the auxiliary FRUs that make up the shelf infrastructure, such as fan trays, power entry modules and alarm panels. In one approach, as shown in Figure 1, each of these FRUs is represented by an IPMC. Some shelf vendors and their customers prefer that approach.