Serialization and asynchronous techniques for reliable network-on-chip communication

Abstract

The Network-on-Chip (NoC) paradigm has been proposed as a potentially viable onchip communication infrastructure for multiprocessor SoC. This thesis investigates the development and validation of efficient links that improve NoC performance, power consumption and reliability. There is emphasis on low-level simulation and validation of the NoC links throughout and gate level circuits are given to provide practical implementations.
The first part of the thesis investigates the use of compression in bit-serial point-to-point links as a means of increasing the available bandwidth of the links in NoC. A bit-serial link reduces the cost of interconnect by reducing the number of wires, but at the expense of reduced throughput. Compression is used to improve the throughput of the serial link by reducing the amount of data transmitted through unused significant bit removal. The compression is performed in real time and the overhead of the extra circuitry is small. The link is modelled in VHDL and simulated to check functionality and correct operation.
The second part of the thesis investigates the development of serial asynchronous links to overcome issues such as power and interconnect area overhead in NoC links. Serialization is used to reduce the interconnect cost of a link by reducing the number of wires needed. The combination of asynchronous circuitry and serialization allows for a lower wiring area and reduced power NoC link, in particular for increased link length. The serial asynchronous link is compared to a fully synchronous link of similar characteristics. Power, area and throughput is compared between the asynchronous and synchronous solutions. Validation is performed on FPGA to confirm the correct functionality of the serialized asynchronous link.
Unreliability due to soft errors is becoming an issue with scaling of technology. The third part of the thesis investigates a novel data coding technique for the asynchronous links developed earlier which offers resilience to soft errors. Resilience is achieved by coding the data using symbols for each bit and a common reference so that transient errors on the NoC link wires can be detected by comparing the symbols and reference to obtain validity of the data and the value of the data. Practical circuits are shown and simulated as well as the area and power estimates.

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