Chapter 15. Clocking

The Previous Chapter

The high speed signaling performed by HT devices is based on point-to-point differential signaling and source synchronous clocking. Details associated with link power requirements and the driver and receiver characteristics are discussed in this chapter. Also, the characteristics of the system- related signals, including RESET#, PWROK, LDTSTOP#, and LDTREQ# are discussed.

This Chapter

This chapter focuses on the source synchronous clocking environment within HT. This involves the use of the source synchronous transmit clock to load data into a receive FIFO and the transfer of data into the receiver time domain with a receive clock that unloads data from the FIFO. Additionally, the specification defines three clocking modes that require different levels of support for passing packets between these two clock domains.

The Next Chapter

The next chapter describes the configuration of devices which use the HyperTransport technology type 1 configuration header for bridges. Such devices include HyperTransport-to-HyperTransport bridges and bridges to other PCI compatible protocols (e.g. HyperTransport-to-PCI or PCI-X). In this chapter, the basic architecture of a HyperTransport-to-HyperTransport bridge is reviewed and the configuration header fields are described. Differences in usage of bit fields by HyperTransport bridge interfaces vs. PCI bridge interfaces are emphasized . The format of PCI compatible bridge headers is formally defined in the PCI-to-PCI Bridge Architecture Specification, Revision 1.1 .