There's a lot that's not being said about the deal announced earlier this week by ARM and Xilinx. What is known is that Xilinx has licensed ARM's Cortex processor IP, and that the two companies are developing next-generation AMBA interconnect technology. But if you read between the lines, you can see where the partnership is likely headed.

First and foremost, what took so long? I wondered for years why Xilinx never adopted the ARM architecture like many of its competitors. The answer lies in the development of the next-generation AMBA bus specification, which Xilinx is calling "an optimized interconnect standard for FPGAs." Xilinx designers likely felt that without this new development, they couldn't get the maximum potential from the ARM architecture, and therefore had no desire to be a "me-too" FPGA vendor.

According to Xilinx, it became clear that at least one of the three main challenges of FPGAs—that they use too much power—figures prominently in the adoption of ARM. The potentially lower power spec came up repeatedly as a key feature that Xilinx wants to exploit.

What Xilinx wouldn't talk about in an interview is which of the ARM cores it plans to deploy in its FPGAs, or whether those cores will appear in its mainstream Spartan products or the high-end Virtex line. Those details won't be forthcoming for at least a few months. But, again, without the correct bus architecture, it wouldn't have mattered since the impact would not have been nearly as significant as it could have been with the proper topology in place.

While the new AMBA spec will likely benefit all ARM processor developers, it includes all the hooks required to maximize the connection within an FPGA architecture. We may eventually see AMBA pervade FPGAs that don't even contain an ARM core, but will be used as the interconnect structure within the FPGA to connect traditional FPGA IP, and replacing current interconnect structures.

Note also that Xilinx and ARM are not alone in the creation of the forthcoming AMBA spec. It also involves industry leaders, like Cadence, Denali, Mentor Graphics, and Synopsys.