A Legacy and a Bright Future for the VMEbus
VME remains the bus of choice for critical applications.
by Ray Alderman, Executive Director, VITA
In October of 1981, three semiconductor companies announced the open-architecture VMEbus, spawned by the introduction of the Motorola 68000 microprocessor. After 27 years, the VMEbus still holds the largest market share of all buses and boards. Today's bus technologies have lives measured in months, so why has the VMEbus survived and prospered while other buses have rapidly gone by the wayside? (Engineers use the terms VMEbus and VME interchangeably.)
Technical reasons explain the success and longevity of VME: First, VME uses an asynchronous bus not tied to a specific clock frequency. That lets VME boards adapt to and adopt newer and faster processors, memories, and I/O devices without making existing boards obsolete. Second, the ability to keep up with technological change was designed into the original bus specifications. Finally, the VME community has continually refreshed the bus technology as companies have offered new silicon chips.
VME products were originally used to replace relay-ladder logic in many industrial applications. Later, when complex applications became event-driven, the bus' interrupt structure provided the only hard real-time deterministic architecture on the market. The VMEbus still offers the only architecture that can handle event-driven, data-driven, and sequencing applications without obsoleting older VME boards. The first VME board, made in 1981, will still operate flawlessly in a VME system designed with the latest silicon.
Because newer silicon devices consume more power, cooling became a major problem. The original VME specification defined and standardized convection, or forced-air, cooling methods. But because many applications--particularly those in military equipment--could not use air cooling, the VME community created the IEEE 1101.2 conduction-cooling spec in the late 1980's. We now face more demanding cooling requirements, so VME vendors and users created the first industry specifications for liquid cooling of electronic circuit boards and chassis.
In the early 1990's, the military adopted VME as its primary architecture in many critical systems, from weapons to aircraft. This decision was based on the technical capabilities of VME, its stable of vendors, and its ability to resist obsolescence. Thus, the VME community had to develop products to operate at extreme temperatures, survive under high shock and vibration conditions, resist dust, dirt, and contaminants, and still offer a long life that approaches 15 years. These demands made VME the highest-performance architecture and the most reliable and survivable open computer standard in the world. No other architecture has come close to the level of reliability and performance of VME.
Over the past ten years, the VME ecosystem has focused on one market segment: critical embedded systems that must work predictably and reliably over very long times. The failure of a critical embedded systems could result in death or serious injury to people, loss of or severe damage to equipment and expensive materials, or environmental harm.
If you analyze the "autopsies" of many dead buses from the past, such as Multibus I and II, STDbus, EISA, and others, you find they all have the same two lethal defects: A synchronous architecture and commodity desktop-PC technologies.
Instead of chasing after each new PC-type bus technology, the VME Industry Trade Association (VITA) and the VME community focus on critical embedded systems. As a group, we now have optical and RF architectures design work underway. We are developing a new Analog Signal Mezzanine Card (ASMC) specifications for software-defined radio cards. And we're developing standards for insertable liquid-cooled power supplies. We continue to develop standards for even more extreme environmental conditions found at high altitudes and space (HAS) applications.
We are developing new standards for FPGA-based mezzanine cards, high-speed serial interconnections (10 GHz and above), revising methods to calculate mean-time between failure (MTBF) specs for electronics, and working on many other system-level specifications. All the equipment sitting on the surface of Mars today is VME-based. You should have no doubts about why NASA chose the VMEbus as the first computer architecture to visit another planet in our solar system. NASA scientists and engineers expected those computer systems to operate for only five or six months. But they continue to work today, some after nearly five years spent in the most inhospitable environment electronics have ever experienced.
So, if you plan to design and build mission-critical embedded systems and they must have extreme capabilities for performance and survivability, the VMEbus is the one to be on.
About the author
Ray Alderman has served as the executive director of the VME Industry Trade Association (VITA) since 1998. Before joining VITA, Alderman served as CEO of PEP Modular Computers, the technical director of VITA, and as a partner in two startup companies that built computer systems for communications, military, industrial controls, transportation, and medical applications.