Making its debut in 1994 as IEEE standard P1386, the PMC (PCI mezzanine card) was successfully adopted for both commercial and government electronic systems. This standard used parallel PCI interfaces. Later, the XMC specification, defined under PICMG VITA 42, extended the PMC card by adding new connectors to support gigabit serial interfaces, including PCIe, and other high-speed serial I/O.
The XMC (Switched Mezzanine Card) is popular for industrial, transportation, and mission-critical systems. It works with industry standard architectures including VME, VXS, OpenVPX, CompactPCI, and CompactPCI Serial in both 3U and 6U form factors. The card is used for special functions, such as signal processing or communications, or as the main processor card in a system. OpenVPX modules are popular SBCs to pair with XMC modules. An XMC processor module can also be used as a standalone processor node. The VITA 42 standard document is still designated as a draft document, but it was released for trial use in 2005. The 42.2 for SRIO and 42.3 for PCI Express are approved.
The XMC standard uses a layered architecture, defining the common mechanical, power and interconnect requirements in the base standard while allowing a number of choices for switched fabrics (PC Express, SeriaRapidIO), as well as application-specific options. The 3U XMC card has one or two 114-pin connectors called the primary (P15) and secondary (P16). Each connector can handle eight bidirectional serial lanes, using a differential pair of pins for each direction. The VITA 42.3 sub-specification defines pin assignments for PCIe, while VITA 42.2 covers Serial RapidIO.
The XMC format has open standards configuration, long-term availability, and ruggedness as well as reliability on its side, but as of yet, there are not a lot of vendors—especially for the processor cards. Keep an eye out, as there will be more coming and they are worth a look.
Kontron Ethernet
The Kontron XMC402 is a dual 10-Gigabit Ethernet communications XMC module. It has PCIExpress x8 and two RJ45 10GBASE-T Ethernet interfaces (copper). The card uses the Intel X540 Ethernet controller IC and has an 8-Mbit serial flash device for boot and a 128 kbit serial EEPROM for configuration data. It takes just 7.5 W, typical and is 74 x 149 mm in size. Operating temperature is 0° to 55°C.
Extreme Engineering Solution Processor
Extreme Engineering Solutions (X-ES) offers the XPedite8101 XMC processor card that uses an Atom E3800 processor with up to four cores and has up to 8 Gbytes of DDR3L-1333 ECC SDRAM and up to 32 Gbytes of SLC NAND flash. It has two Gigabit Ethernet ports, a DisplayPort video interface, four USB 2.0 ports, two RS-485 ports, and up to two SATA interfaces. Wind River VxWorks and Linux board support packages, as well as Microsoft Windows drivers, are available for the XPedite8101. Operating temperatures as high as -40° to 85°C are optional, and the board is rated for shock and vibration. The board is also available as the XPedite8150 rugged COM Express module.