Specifications

A–6 System Address Mapping
Subject to Change – 17 January 1997
21164 Address Space Configuration Supported by the CIA
The CIA generates 32-bit PCI addresses but accepts both 64-bit PCI address cycles
(DAC
1
) and 32-bit PCI address cycles (SAC
2
). The following window restrictions
apply to PCI main memory accesses:
•
Window 4, the “Monster Window,” provides full access to main memory. It is
accessed by DAC cycles only with PCI address bit <40>=1. Memory address
bits <33:0> equal PCI address bits <33:0>.
•
Window 3 can be accessed either by DAC or SAC cycles, but not both. If using
DAC cycles, the following three restrictions apply:
– PCI address bits <63:40> must be zero
– PCI address bits <39:32> must match the DAC register
– PCI address bits <31:0> must hit in window 3.
•
Windows 0, 1, and 2 accept only SAC cycles.
Figure A–5 shows how the 21164 address map translates to the PCI address space. It
also shows how PCI devices access 21164 memory space via DMAs. Notice that the
PCI memory space is double mapped using dense and sparse space.
1
Dual-address cycle (PCI 64-bit address transfer)-used only if address bits
ad<63:32>
are
nonzero.
2
Single-address cycle (PCI 32-bit address transfer).