I hear you NOCing, But Can You Close Timing?

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Network on Chip (NOC) IP has been around for a while. I wrote an article about academic research papers on NOCs presented at the seventh annual International Symposium on System-on-Chip conference held in Tampere, Finland in late 2005. NOCs were the conference's theme back then and the jury was out on using NOCs to interconnect large IP blocks, including processors, network controllers, and memory on SoCs. NOCs introduce overhead that wasn't particularly welcome back in 2005. Today, it's a different story. Interconnect complexity has risen with general SoC design complexity, as you can see in Figure 1.

www.eejournal.com/, Apr. 03, 2023 – 

Figure 1: Chip complexity has increased exponentially over the past 50 years, just as predicted by Gordon Moore in 1965.

The orange triangles in Figure 1 show the exponential rise in SoC transistor count in line with the original Moore's Law prediction from 1965. It's amazing how consistent this increase has been decade after decade. However, the blue circles and green squares tell a different story. This data, depicting single-thread processor performance and clock frequency graphically depict the death of Dennard scaling. The red triangles show a leveling off of power consumption at around 100 to 200 watts. That's more a function of the maximum thermal dissipation of the device package.

But the black diamonds in Figure 1 show that, since around the year 2005, the number of IP cores laid down on an SoC has risen dramatically. Consequently, and not shown by Figure 1, the interconnect complexity among these many on-chip cores has also risen dramatically. And that rise has not been just quantitative. It's not just that there are more interconnects. The role of on-chip interconnect has also grown more complex. It's no longer sufficient to connect two IP cores with a simple interface so that they can pass data between themselves. There are new considerations, including memory management, cache coherency, data security, encryption, compression, interface translation, and consistency checking to deal with as well.

Because of these changes, the NOC's time has come. In fact, according to Michal Siwinski and Frank Schirrmeister, respectively the CMO and the Vice President for Solutions & Business Development at Arteris, the inflection point for NOCs really began around 2010 or 2012 with the transition to the 28nm process node, which coincides nicely with the rise in the number of cores per chip shown in Figure 1. That's when complexity reached the point where NOCs really started to make sense.

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