DECchip 21171

This document is the DECchip 21171 Core Logic Chipset Technical Reference Manual, a preliminary edition from September 1995. It serves as a support and reference guide for engineers designing uniprocessor systems using the Alpha 21164 microprocessor.

The chipset (DECchip 21171) is composed of two main types of integrated circuits:

1. DECchip 21171-CA (CIA - Control, I/O Interface, and Address chip):

   • Functions as the host bridge to the 64-bit Peripheral Component Interconnect (PCI) bus.
   • Provides control functions for main memory, the Data Switch (DSW) chips, and parts of the I/O data path.
   • Manages various system transactions, including CPU read/write operations (to cacheable and non-cacheable space), and Direct Memory Access (DMA) read/write transactions.
   • Handles address mapping for memory and I/O, supporting both direct and scatter-gather translation via a Translation Lookaside Buffer (TLB).
   • Implements system data coherency protocols.
   • Features a comprehensive set of Control and Status Registers (CSRs) for programming memory timing, system configuration, error handling, and performance monitoring.
   • Details power-up and initialization procedures.

2. DECchip 21171-BA (DSW - Data Switch chip):

   • Four DSW chips are typically required to implement the full data path.
   • Provides bidirectional data paths between the Alpha 21164 microprocessor, main memory arrays, and the CIA.
   • Primarily consists of data buffers (including victim, I/O read, I/O write, and DMA buffer sets) and multiplexers to manage data flow.
   • Supports various ECC-protected data path widths: 64-bit between CIA and DSW, 128-bit between the 21164 and DSW, and 256-bit between DSW and memory.
   • Its operations are controlled by commands and signals from the CIA.

In essence, the document provides detailed information on the architecture, pin descriptions, functional units, transaction mechanisms, address mapping, and register definitions necessary for integrating the DECchip 21171 core logic chipset into high-performance Alpha 21164-based computer systems, supporting up to 8GB of ECC-protected physical memory and high-performance PCI.