Adding NoCs To FPGA SoCs 

June 28th,  2018 – By Ann Steffora Mutschuler

As complexity and device sizes rise, so does the need for an on-chip network.

So are today’s FPGA SoCs enough like traditional, digital SoCs that all the same rules apply for a network on chip? The answer appears to be somewhat, but not completely.

“Both of the main FPGA vendors have proprietary network-on-chip tools, and if a user chooses to use one of those, they can hook up their functions using a form of network on chip,” said Ty Garibay, CTO of Arteris IP. “It is more of a conceptual approach to the system. Does it look enough like a standard SoC that it makes more sense to think of it as having a NoC as the connectivity backbone? Many FPGA applications do not. They look a lot more like a networking chips or backbone chips that are fundamentally data flow. Data comes in the left, you have a whole bunch of a munging units, and data goes out the right. That is not a traditional SoC. That’s a normal network processor or baseband modem or something like that, where it’s a data flow chip. So in those types of FPGA soft designs, there’s no need for a network on chip.”

But if it conceptually looks like a bunch of independent functional units that communicate with each other and are controlled generally by a central point, then it does make sense to have those connected with a soft network on chip, he said. “The next generation of high-performance of FPGAs are expected to contain hard NoCs built into the chip because they are getting to the point where the data flow is at such a high rate—especially when you have 100-gigabit SerDes and HBM2, where trying to pipe a terabit or two per channel through soft logic essentially uses all the soft logic and you’ve got nothing left to be processing with.”

As a result, that bandwidth is going to require a hardening of the data movement that is enforced in much the same way that processing enforces hard DSPs or hard memory controllers. Successive generations of FPGAs may be expected to look like a checkerboard of streets, where the streets are hard 128, 256, 512 12-bit buses that go from end to end in one or two cycles and don’t use up any soft logic to do it.

“Along with this would be the synthesis function that allocates on-ramps and off-ramps to those channels as part of hardening the function onto the FPGAs, because we’re moving so much data around I just don’t see how they can continue to do that in soft logic,” Garibay said. “That will be the coming of real NoCs onto FPGAs, because NoCs are always a good idea.”

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https://semiengineering.com/adding-nocs-to-fpga-socs