An industry perspective from Curtiss-Wright Controls Defense Solutions
Understanding FMC interoperability
maximum number of FPGA connections. Thus, the FMC’s I/O devices are very intimately connected to the host card’s FPGA. There are no buses such as PCI to contend with. But this flexibility requires more direct control. The exact FPGA connectivity – for example, which pins are utilized and FPGA type – needs to be considered. All FPGA hosts will be different, even within a family such as a Xilinx Virtex-5 SX95T and a Xilinx Virtex-5 SX240T.
LPC and HPC defined
The FPGA tools environment is also critical. When a single vendor supplies both the host processor and the FMC card, it will be easier to supply software/HDL optimized for the low-level connectivity of the host and its environment. Sometimes, though, it is preferable to use an FMC and a host card from different vendors. FMC allows for two sizes of connector, Low Pin Count (LPC) and High Pin Count (HPC), each offering different (maximum) levels of connectivity, analogous to how some PMC boards have a 32-bit interface while others have a 64-bit interface by using an additional connector. The LPC offers up to 68 differential pairs while HPC offers up to 80 differential pairs. Curtiss-Wright Controls Embedded Computing’s (CWCEC’s) FMC-516 (Figure 1) is a quad-channel, 250 MSps, 16-bit analog input card that enables I/O devices to be directly coupled to a host FPGA. By providing direct ADC connection to the host FPGA, this card ensures maximum throughput and enables multiple channels and boards to be synchronized.
FMCs with HPC connectors cannot usually be used on LPC FMC hosts. The LPC is a subset of HPC and so some combinations yield reduced functionality. But HPC FMCs will typically not work on LPC host boards. Also, not all HPC FMCs can be used on every HPC FMC host. And there are FMCs with more connectivity requirements than some hosts can provide, even if the host is identified as an “HPC FMC” host. As FMCs continue to increase in popularity, thanks to their high-bandwidth, low-latency interfaces, lower power, and increased I/O real estate, it is important to be familiar with the differences between different classes of FMC cards so that interoperability can be maximized and the benefits of these flexible, compact I/O cards are optimized.