One of the main problems when designing large ASICs today is to distribute a low power synchronous clock over the whole chip and a lot of remedies to this problem has been proposed over the years. For Networks-on-Chip (NoC), where computational Resources are organised in a 2-D mesh connected together through Switches in an on-chip interconnection network, another possibility exists: Globally Pseudochronous Locally Synchronous clock distribution.In this paper, we present a clocking scheme for NoCs that we call Globally Pseudochronous Locally Synchronous, in which we distribute a clock with a constant phase difference between the switches. As a consequence of the phase difference, some paths along the NoC switch network become faster than the others. We call these paths Data Motorways. By adapting the switching policy in the switches to prefer data to use the motorways, we show that the latency within the network is reduced with up to 40% compared to a synchronous reference case.The phase difference between the resources also makes the circuit more tolerant to clock skew. It also distributes the current peaks more evenly across the clock period, which lead to a reduction in peak power, which in turn further reduces the clock skew and the jitter in the clock network.
Power consumption in clock of large high performance VLSIs can be reduced by adopting Globally Asynchronous, Locally Synchronous design style (GALS). GALS has small overheads for the global asynchronous communication and local clock generation. We propose methods to a) evaluate the benefits of GALS and account for its overheads, which can be used as the basis for partitioning the system into optimal number/size of synchronous blocks, and b) automate the synthesis of the global asynchronous communication. Three realistic ASICs, ranging in complexity from 1 to 3 million gates, were used to evaluate GALS benefits and overheads. The results show an average power saving of about 70% in clock with negligible overheads.
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