VITA 57.4: FMC+

Field-programmable gate arrays (FPGAs) are utilized in many applications, with the range expanding as new variations of FPGAs emerge. By design, FPGAs are easily reconfigured as application needs change. But sometimes a change to the front-end hardware connecting the FPGA to a real-world application must also change. Until the advent of the FPGA Mezzanine Card (FMC), there was no universally accepted way to modularize the I/O. FMC must now continue to improve in order to meet the latest wave of performance requirements.

, ANSI/VITA 57.1, is a very popular mezzanine card standard used in many different applications. It is host form factor independent, so you will find it used in everything from motherboards to . The standard was driven and developed by the community to modularize I/O into an FPGA. As a result, it has established itself as the go-to mezzanine when using an FPGA.

However, the original standard, ratified in 2008, needed a performance boost to keep up with today’s faster . Gigabit serial interfaces at speeds approaching 32Gbps [Gigabits per second] necessitated an update to the standard.

Efforts under the VITA 57.4 working group were started in 2014 to make improvements to FMC. The primary goal of the working group was to extend the Gigabit transceiver support specified in the VITA 57.1 standard. A basic premise of the working group was to maintain backward compatibility between new VITA 57.4 carrier cards and existing VITA 57.1 mezzanine modules. VITA 57.4 was quickly dubbed FMC+ by the working group.

After a few false starts by the working group, the team at Samtec stepped up to take on the daunting task of bringing the efforts to a conclusion (See Figure 1). It took well over two years, but the efforts were rewarded in July with the final accreditation of the ANSI/VITA 57.4-2018 “FPGA Mezzanine Card Plus (FMC+) Standard” both by ANSI and VITA.

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Figure 1: Samtec SeaRay Connector.

FMC+ extends the original FMC standard by specifying two new connectors that enable additional Gigabit transceiver interfaces that run at up to 28Gbps. It also describes FMC+ I/O modules which support this enhanced version of the FMC electro-mechanical standard. Additional signals to support a backplane reference clock and synchronization have been added. The VITA 57.4 standard is backwards compatible in that a VITA 57.4 carrier card can still support a VITA 57.1 FMC.

Two new connectors provide FMC+ capability. The High Serial Pin Count (HSPC) connector is in a 14 x 40 configuration yielding 560 pins. This increases the number of multigigabit interfaces from 10 to 24, capable of data rates up to 28Gbaud in each direction.

FMC+ also specifies an optional High Serial Pin Count extension (HSPCe) connector in a 4 x 20 array yielding an additional 80 pins. This supports up to eight additional multigigabit interfaces. Utilizing both HSPC and HSPCe connectors presents 32 links capable of data rates up to 28Gbaud in each direction.

The standard defines air-cooled versions, which extend to cover a ruggedized conduction-cooled variant, making FMC+ ideal for a broad spectrum of operating environments.

Up to triple width modules are specified to facilitate applications requiring additional carrier card bandwidth, greater space on the front panel, or a larger PCB area.

A large ecosystem of FMC+ host and module suppliers have been expanding the market beyond Converter ()/ Converter () products. Several optical, Radio-Frequency (RF), and () configurations have been released or are currently in development.

The work is not done. VITA 57.1 is open for some updates by the working group. The team is also anxious to provide better tools and guidance to both host and mezzanine developers in the form of additional standards under VITA 57.5 “Physical Tool to Aid FMC+ Development.” Their project list includes:

  • Loopback Cards – development tool for FPGA designers looking to test and confirm signal integrity between mezzanines and carriers.
  • Jumper Cables – appropriate for users looking to extend FMC+ signals over distances greater than the defined 8.5mm and 10mm stack heights.
  • Jackscrew Standoffs – useful to ease separation of FMC configurations with high-pin counts (i.e. double and triple wide FMC+ cards utilizing HSPCe).

Even this is not the end of efforts. The team is also looking at analysis and simulation tools that would make selecting compatible hosts and modules much easier for integrators.

Companies interested in the development of the FMC standards are encouraged to contact VITA (www.vita.com) to learn how become involved in the evolution of FMC.