Low-Level SCI Protocols and Their Application to Flexible Switches

The purpose of SCI is to provide a fast interconnection technology for up to thousands of components. This chapter discusses several aspects of the protocols used in SCI, especially regarding requirements and possibilities for their implementation in hardware. One motivation behind the SCI standardization effort was to enable SCI as interconnect for peripherals or memory subsystems. Therefore, we discuss how the protocols can be implemented efficiently and in a small chip area. The first part deals with the data format of SCI packets (Section 5.2), the protocols for allocating buffer space (Section 5.3) and bandwidth (Section 5.4). In the second part, the architecture of current switches is taken as a starting point for elaborating further demands and consequences for switch architectures. One particular design question (strip-off decision) is discussed in detail and an implementation option is given. A major issue of this chapter is the introduction of the rule-based description method for routing algorithms in Section 5.7. It is not only used to describe the examples of the strip-off decision but it reveals a general approach to implementing routing methods for high-speed networks.