Upcoming AdvancedTCA Base Extensions specification benefits current and future systems - including for cloud
The AdvancedTCA (ATCA) Base Extensions (PICMG 3.7) specification supports larger systems with the horsepower to handle deployment in cloud and datacenter applications, while also emphasizing compatibility with original AdvancedTCA (PICMG 3.0) platforms and boards. In addition to extended blade and shelf area, PICMG 3.7 includes enhanced Hardware Platform Management (HPM) capabilities, such as a complete description of the system power geography, much of which can be integrated into existing ATCA systems.
As the ATCA initiative pushes into its second decade, a significant set of extensions is nearing completion in PICMG 3.7 – the ATCA Base Extensions specification. This new specification emphasizes compatibility with the existing billion-dollar ATCA ecosystem based on PICMG 3.0, but also enables larger and more powerful ATCA shelves and boards, as well as a further strengthened HPM layer.
Regarding larger and more powerful ATCA shelves, PICMG 3.7 defines shelves that can accommodate 16 double-wide ATCA boards, 8 on the front and 8 on the rear of a dual-sided shelf, with each board drawing up to 800 W. An alternate dual-sided shelf could support 32 single-wide 400 W ATCA boards, half on each side. The PICMG 3.7 HPM layer adds support for such configurations, but also includes extensions that can benefit already shipping ATCA systems.
What HPM measures are needed for large PICMG 3.7-based systems?
Figure 1 shows two example shelves – supervised by a single System Manager – of the sort that PICMG 3.7 enables.
The shelf on the left has up to 16 single-wide front boards, each paired with a PICMG 3.7 defined Extended Transition Module (ETM), which is like a normal ATCA Rear Transition Module (RTM), except that it is the size of an ATCA front board. Just like ATCA RTMs, ETMs mate with their corresponding front boards via implementation-defined connectors, are powered from that front board, and are represented in the HPM layer by the front board Intelligent Platform Management Controller (IPMC). Using front board-sized ETMs dramatically increases the board real estate available compared to a front board plus RTM pair in PICMG 3.0. Furthermore, both front boards and ETMs could be double-wide (with a maximum of eight each), further increasing the implementation envelope for a front board plus ETM pair. Finally, note that the Ethernet-based Base Interface in a PICMG 3.7 shelf optionally supports 10 Gbps, not just 1 Gbps, communications.
The shelf on the right in Figure 1 has up to 32 single-wide front boards, half on the front (side A) and half on the rear (side B). Alternatively, a shelf like this could accommodate 16 double-wide boards, half on each side. The key thing to understand about these dual-sided shelves is that many existing cabinets are already deep enough for them; the floor area for the unused portion of those cabinets is essentially wasted. Of course, there are cooling challenges associated with filling that space with active electronic components.
The HPM layer extensions needed for PICMG 3.7 shelves like Figure 1 depicts include support for dual-sided shelves with up to 32 boards, thorough support for double-wide boards (which are allowed, but not strongly supported in PICMG 3.0), awareness of the 10 Gigabit Base Interface option, and support for new board types like ETMs. It has been challenging to cover these extensions while maintaining maximum compatibility with the original ATCA conventions for operators, management applications, and specification-defined HPM data structures and commands.
Are larger, more powerful systems like those shown in Figure 1 actually needed? ATCA-derived but OEM-specific platforms being developed and/or delivered in 2013 suggest that the answer is “yes.” One of these platforms, the BTI 7800 Series from BTI Systems, summarized in Sidebar 1 (Page 16), creates a fabric for cloud-based service delivery that links inter-datacenter networking facilities and cloud services customers. Another such platform (which is not yet public) has 28 single-wide ATCA slots: 14 on the front and 14 on the rear of a dual-sided shelf. Neither of these platforms is based on PICMG 3.7 since the specification was not far enough along at the time these platforms were designed, but future platforms could certainly benefit from a standardized framework for such advanced platforms.
How can PICMG 3.7 improve the HPM layer for existing AdvancedTCA systems?
Figure 2 shows the power architecture for an example AC-powered ATCA shelf with annotations showing one type of HPM information that PICMG 3.7 enables. There are several notable aspects in the example, which could show one side of a dual-sided horizontal slot shelf supporting four double-wide boards on each side:
- Only half the slot positions have connections to the backplane for power (signified by blue connector blocks in Figure 2) because this shelf has been designed to support only double-wide boards. Slots without power connectors are called void slots in PICMG 3.7 (see slot ØA6 in Figure 2); a PICMG 3.0 board cannot be installed in such a slot because it cannot be powered there. Similarly, a void slot takes up no management or fabric resources, optimizing the shelf for double-wide boards. Nevertheless, a void slot gets the full cooling allotment of a normal slot position, so a double-wide PICMG 3.7 board can draw up to 800 W.
- With PICMG 3.7, the entire power path feeding a given board input (such as the blue input or the green input to slot A7 in Figure 2) is described by HPM data structures, including the relevant PSUs and PEMs. In contrast, PICMG 3.0 has no provisions for identifying the PEM and PEM output that feeds a particular board input, or identifying any information at all regarding PSUs.
PICMG 3.7 allows the complete “power geography” of a shelf to be described (that is, the entire power supply path for each power input for Field Replaceable Units (FRUs), including boards) in the shelf. As shown in Figure 2, if the fuse on one of the inputs to the double-wide board in slot A7 blows for some reason, the HPM layer (and its clients at the higher level) can know that power to that board now depends entirely on PEM B and PSUs 4-6. Any request by an operator to remove PEM B must be declined unless it is acceptable for that board to lose power. Similarly, if the PSUs are organized on an N+1 redundancy basis, only one of them can go down or be removed without impacting the power supply to all the green feeds, likely critically affecting the board in slot A7.
What if the example shelf of Figure 2 were installed in a non-redundant power configuration (say, with PEM B and PSUs 4-6 entirely missing)? In PICMG 3.0, voltage sensors on the green feeds of each of the boards could produce a continuing blizzard of alerts about an unpowered feed. With PICMG 3.7 facilities, a board can check the expected voltage on each of its feeds. If the expected voltage is zero, the board has no need to generate such alerts.
Are the facilities above useful for existing shelves designed to the base ATCA specification? The power geography extensions described previously can be directly relevant. Consider, for instance, the Schroff AC-powered shelf described in Sidebar 2. It has no void slots, but otherwise would directly benefit from the power geography facilities of PICMG 3.7, including PSU-awareness and a full description of the complete power path for each FRU input.
There is also another way that PICMG 3.7 HPM facilities can benefit existing shelves designed for standard ATCA: PICMG 3.7 enables extended sensors that can support wider range and/or more accurate sensor values than base ATCA.
How can PICMG 3.7’s extended sensors benefit existing ATCA shelves?
The Intelligent Platform Management Interface (IPMI), which is the foundation for ATCA’s HPM layer, limits physical sensor values, such as for voltage or current, to 8 bits in size. This limitation is fine for HPM purposes in many cases, such as for temperature sensors, which can easily be accommodated in 8 bits. In some power contexts, however, the limitation to 8-bit sensor values can be constraining. Consider the DC-powered Schroff shelf in Sidebar 2. The PEMs in that shelf include a current/power monitor device that can be configured to deliver 9- through 12-bit measurements, but with the current PICMG 3.0 HPM layer, precision must be sacrificed to fit these measurements in 8 bits. PICMG 3.7 allows 16-bit sensor values, eliminating this sacrifice.
Extending AdvancedTCA for today and tomorrow
PICMG 3.7, now nearing completion within PICMG, can benefit large systems, some of which may be proprietary architectures that simply leverage the HPM architecture of ATCA and potentially PICMG 3.7. This new specification can also benefit existing ATCA systems, especially with its strengthened HPM layer.
Pigeon Point Systems