Chapter 19. Networking Extensions Overview

The Previous Chapter

HT provides a variety of mechanisms to support power management. These mechanisms include LDTSTOP#, LDTREQ#, STPCLK messages, and STOP_GRANT messages. While these mechanism are optional for HT devices, the specification requires this support for x86-based platforms. Note also that functions other than power management may make use of these signals and messages. The previous chapter discusses the strategy employed by HT for implementing power management and how a given platform can use these mechanisms to support power management.

This Chapter

This chapter summarizes some of the major additions to the HyperTransport protocol which will be forthcoming in Release 1.05 and Release 1.1 of the specification. Collectively, these additions are referred the HyperTransport Networking Extensions, and target some of the special requirements of communications processing. Key features include a message passing protocol for larger packets, a formal definition for switch devices, a link-level error recovery method, sixteen optional additional posted write virtual channels with defined arbitration and bandwidth allocation, direct peer-peer transfers, an increase in the number of outstanding transactions for host bridges, and a 64-bit addressing option.

The Next Chapter

HT is designed to support a variety of I/O and processor buses via bridges. The specification defines specific requirements for supporting PCI, PIC-X, AGP, and processor buses. The next chapter discusses these support requirements.