A–6
System Address Space
PCI Address Space
Figure 1–2 Memory Remapping
1.2 PCI Address Space
The system generates 32-bit PCI addresses but accepts both 64-bit address (DAC
1
)
cycles and 32-bit PCI address (SAC
2
) cycles. Accessing main memory is as follows:
•
Window 4, the “Monster Window,” provides full access to main memory. It is
accessed by DAC only with ad<40> equal to 1. Memory address addr_h<33:0>
equals PCI address ad<33:0>.
•
Window 3 can be either DAC or SAC, but not both. If DAC, ad<63:40> must be
zero, ad<39:32> must match the DAC register, and ad<31:0> must hit in win-
dow 3.
•
Windows 0, 1, and 2 are SAC-only.
1 Dual-address cycle (PCI 64-bit address transfer) requires that address bits <63:32> con-
tain a nonzero value.
2 Single-address cycle (PCI 32-bit address transfer) requires that address bits <63:32> con-
tain a value of zero.
LJ-05396.AI4
21164 CPU
Cached Memory Space (8GB)
PCI Memory
Space
Scatter-Gather
Map
Direct Map
PCI Window
PCI Window
8KB
Page
