Evolution of a small form factor

Highly integrated with low SWaP, VITA 73 fits perfectly on the small side of the rugged small form factor space.

2Computing systems used in rugged applications have traditionally been designed from scratch using
semiconductor-level components. As COTS system-level technology has increased in availability and popularity, the designers of these rugged systems have looked for more integrated levels of technology. These designers would like to leverage the cost effectiveness and time-to-market advantages of COTS boards and systems. Until recently, they have had few choices. That is rapidly changing as the list of possibilities grows. One of those compelling and emerging options in the small form factor arena is VITA 73 (Rugged Small Form Factor).

What began as a solution to a network attached storage problem soon turned into one of the newest small form factor system solutions for rugged embedded computing platforms. Struggling to find a suitable method to package a Solid State Disk (SSD) or a hard drive, PCI Systems CEO Claus Gross pondered a 2.5-inch “X-frame” carrier for SSDs that had been sitting on his desk for some time. Suddenly, on a Monday morning, it struck him that this was just the right size and form factor for a next-generation embedded computing platform.

Many customers over the previous months had commented that they could really use a small-sized system package that was conduction cooled and capable of using the latest in high-performance, processors. A set of requirements soon emerged that would inspire the design for a next-generation platform. The modules they required must:

  1. Be small yet high performance.
  2. Be rugged, conduction cooled, and completely closed for robust shielding.
  3. Be usable in blade configuration with a backplane or as a mezzanine on a carrier by simply replacing the interconnect connector.
  4. Be able to operate in a stand-alone mode if necessary, precluding the need for other modules.

These requirements expanded the thought process to include developing a platform with an industry leading function-to-size ratio. This ratio or functional density needed to be higher than anything currently on the market in this class of product. The higher functional density would be key to lowering total system costs because fewer modules would be needed.

These requirements led to the development of a specification for a new rugged embedded computing platform. And PCI Systems brought this specification to the VITA Standards Organization (VSO) to complete the work and turn it into an industry standard. A working group was formed in 2010 under VITA 73 to start the process. VITA 73 was submitted as a specification describing a small, rugged form factor for board modules and the associated backplane profiles. Also included was a specification for standard I/O using MIL-DTL- to make the standard even more desirable for rugged deployments.

VITA was chosen as the most appropriate place to conduct this work because of the dedication of the members to develop open standards for the critical embedded computing market. The experience of the members and the recent work on made the decision even easier. VPX was the impetus for the module interconnect methodology and is used as the basis for the interconnection portion of the VITA 73 specification.

Further requirements helped to guide the development of VITA 73. A complete system or box-level solution was highly desirable. Users of this new platform were not to be burdened with the worry of the integration challenges that other architectures often imposed. The combination of primary and secondary requirements quickly led to a box that did not require wedge locks to retain the modules, as those would have used too much of the premium board real estate defined in the small form factor. The box would instead completely enclose the modules, providing both cooling and secure confinement for rugged usage models.

VITA 73 features

How well does VITA 73 match up to its original design requirements? Let’s look at some of the key features of the specification to find out.

Size: VITA 73 modules are 3 inches wide by 4 inches deep. They are designed to be housed in an enclosure that can have from 4 to 16 slots. The total package for an eight-slot chassis is 4.5 inches wide by 4 inches high by 6 inches deep. This certainly puts VITA 73 firmly in the small end of small form factor platforms yet provides plenty of room for expansion when an application calls for a larger system. Also, the ties to VPX give an additional option to expand into a full VPX system if necessary.

Weight: Size, Weight, and Power (SWaP) are major concerns for many platforms in a multitude of industries. A VITA 73 chassis, when empty, is no more than 1.5 KG in weight (slightly more than 3 lbs). Fully loaded, with a typical payload of modules, results in a box less than 2.5 KG (5 lbs), making this a very lightweight contender. The clamshell packaging eliminates the need for heavy and bulky wedge locks on the printed circuit boards and saves board real estate for valuable functions (Figure 1).

21
Figure 1: The VITA 73 clamshell packaging eliminates the need for heavy and bulky wedge locks on the printed circuit boards and saves board real estate for valuable functions.
(Click graphic to zoom by 1.9x)

Power: VITA 73 is specified to disperse up to 120 W in an eight-slot cold-plate-cooled chassis. With its conduction-cooling packaging, it can handle most of today’s highest-performance processors, giving it an edge in both electrical and computing power. Computing performance is maintained between modules by using PCI Express as the module interconnect fabric. Modeled after the VPX specification, it can handle similar data speeds between modules. The connectors chosen for the standard are specified to handle 10 GHz signals. To keep the design simpler, interconnects between modules are limited to a star-only topology. This reduces latency, making the overall system faster. It also simplifies the fabric switching between modules, requiring no switching on the modules. VITA 73 uses PCIe Gen2 with a bus width of four lanes and a possibility for a bus width of eight lanes per slot.

Other advantages of VITA 73

Pin-in-socket connectors are used instead of blade-edge connectors, improving system reliability. Readily available straight connectors can be substituted for the right-angle connector to allow the creation of a family of mezzanine modules using the same exact design.

Zero cables and wires are used to interconnect the modules to the I/O connections. PCI Systems’ “No Wires” strategy is used throughout. Wires in rugged applications are not a solution. They will vibrate in the chassis and eventually break at the solder points. Small printed circuit boards are used instead to route signals between modules and I/O connectors, enabling high-speed differential signaling with carefully matched impedance for the high signal speeds. Additionally, assembly and maintenance are simplified because the interconnect modules prevent missed or wrong connections and reduce failures caused by vibration.

Six backplane profiles are defined to accept processing modules, two types of peripheral I/O modules (single-ended and differential), and RF input modules, SATA drives, and power supplies. Allowing for RF coax inputs provides a very reliable and readily available I/O connection.

There are several bonus features included in VITA 73. A 10 MHz single-ended frequency is defined to aid in systemwide and synchronize power supplies. Also a star trigger and other trigger functions are implemented. For next generations of PCI Express, the usage of the PCIe 100 MHz clock is defined for all boards used in the chassis and a separate instrumentation frequency of 100 MHz is part of the specification.

Market needs

The analysis of the current market for military computers has shown that the market interest in very small, ruggedized systems is very high, especially for unmanned aircraft with highly integrated electronic control systems. This has spurred interest in the military hardware community to push for development of a standard for a small form factor system.

A new market

Complimentary to VITA 73, there is also a new VITA 71 working group, which is creating a 3U/6U VPX mezzanine board standard that is also compatible with VITA 73.

The VITA 73 working group is on-time and on-track to position itself as “the standard” for unmanned systems, securing all members’ and interested parties’ early stakes in the new market.

Topics covered in this article