Global interconnect analysis

• The rapid development in deep submicron (DSM) technology makes possible to design complex billion-transistor chips. To take full advantage of increased integration density and cope with the difficulties in designing such complex systems, the emphasis of design methodology has changed from gate-level design to the exploitation of intellectual property (IP) blocks. This IP-based design is rapidly becoming the dominating design paradigm in System-on-Chip (SoC) era. IP blocks themselves are usually verified by the supplier for some technology node but the problem is how to ensure the correct performance when the IP block is integrated in the SoC or even in Network-on-Chip (NoC) environment. The problems occur in adapting the block interface into the used communication frame. The main objective is to make computation (IP blocks) and communication independent on each other. Due to increasing integration density and diminishing wire dimensions, communication using traditional SoC interconnect schemes (such as buses) does not scale up properly compared with system complexity. This leads to the communication scheme where traditional buses and their arbitration are replaced with network switches connecting various IP blocks in different network nodes to each other. Thus, a shift from SoC to NoC is predicted when system complexity scales up on chip level. Network nodes bring inherent pipelining and buffering onto system level which is important when dealing with global wires that have more resistive and inductive nature in current and future DSM technologies. Additionally, undesired transmission errors can be reduced with errorchecking, e.g. in each network node. In this case, latency may increase as a result of increased reliability. In this chapter, we first discuss parasitic modeling in the presence of crosstalk and delay modeling of global wires. Inductance issues are discussed in more detail in chapter 5 and thus we omit them here. Some possible interconnect schemes in SoC and NoC are shortly discussed. In section 3.3 we evaluate cost functions (e.g. power consumption and area) that IP blocks set for the global communication network. We present a method how to evaluate those costs in the early phase of design. By evaluating costs of those resources we can better optimize global interconnects to meet both signal and power distribution challenges. We present one case study example on the cost evaluation. Finally, in section 3.4 we apply methods and theories presented in earlier sections and optimize global interconnects to meet different constraints. The delay in global wires is optimized using repeaters that are sized properly and placed in proper distances so that the overall delay is optimized. Then we present optimal signaling having maximum throughput as a constraint. Last, we present a case study in which both power and signal distribution are simultaneously optimized. This is done by using a method called interconnect partitioning and the design constraint in this case is the maximum allowed variation of power supply levels in the power distribution network. The variation depends on the grain size of the power distribution grid and power consumption taking place in IP (or functional) blocks due to simultaneous switching of large amount of logic gates in a very short time interval.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

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