We live in an era in which integrated circuits, whether in the form of several chips or in the form of a single one, are increasingly complex and composed of more and more parts that have to be interconnected with each other and this has become in one of the problems faced by engineers. The term NoC , which stands for Network on a Chip and translates to network on a chip, is one of the most common types of heterogeneous electronic circuits. But what is your organization, what do they consist of and what is the reason for its existence?
Clarification: in this article we refer to the different processors within a SoC or a NoC as processing elements or PE , and these can be any element within one of these infrastructures, so they can refer to a CPU, a GPU, a DSP, an NPU, etc.
Internal communication in an SoC and its limitations
We use SoCs continuously, and it is that in reality today all the processors that we use both in our PCs and in our smartphones are SoCs, but one thing that many people do not get to ask is: how do the different elements of communication communicate? processing on an SoC? In which part of an SoC does the communication of all its processing elements occur? Well, in the north bridge, which is the part that communicates the different processing elements with each other and these with the memory, the most common structures being the Crossbar Switch and the communication rings.
The Crossbar Switch is made up of a series of switches communicating between them in the form of a matrix, where each of the processing elements that make up the electronic circuit is connected to one of these switches and the data transmission is carried out by activating the different extreme switches. to extreme; For this, the Crossbar Switch has a small internal control system in charge of managing the different data shipments between the different parties.
The ring configuration, on the other hand, is a bit more complex and a simile to explain it in the simplest way possible is the roundabouts. In this organization, the data packets are those that circulate through the roundabout and go through a segment of it in each clock cycle, leaving the ring when they reach the segment where the destination element is connected.
The main problem in both cases is that when a new system derived from an existing one is created by changing a single element, even if it is under the same architecture, the communication infrastructure has to be rebuilt.
In addition, the problem is created that as we add processing elements to the infrastructure that communicates them, it grows more and more and exponentially, to the point where it ends up occupying more than the processing elements to communicate and at that point where it is necessary to adopt other communication infrastructures.
Intercom on a Network on a Chip
The NoC or Network on a Chip seek to solve the scalability problems of the SoCs, thus allowing more complex structures than the one they allow.
Instead of building a very complex communication infrastructure as occurs in SoCs, in the case of NoCs what is done is adding a router (R) and a network infrastructure (NI) connected to each element. The idea is that when a PE wants to communicate with another PE, it only has to “call the number” of the other processing element with which it wants to communicate, and then the routers located in each of the parties get in touch and data is transmitted between them.
The biggest advantage of this is that it allows creators of heterogeneous systems to create new structures without having to create a complex communication infrastructure, and it also allows them to create variations of their architectures much faster than using other communication systems thanks to that the communication structure is found not outside the different PEs but within each one of them, facilitating the creation of scalable architectures in terms of the amount of processing elements.
