Specifications

17 January 1997 – Subject to Change

System Address Mapping A–35

PCI-to-Physical Memory Addressing

A.4.3 Scatter-Gather Addressing

When Wn_BASE[Wn_BASE_SG] is set, the translated address is generated by

using a table lookup. The table is referred to as a scatter-gather map.

The incoming PCI address is compared to the PCI window addresses for a hit. The

Tn_BASE of the window that was hit is used to specify the starting address of the

scatter-gather map table in memory.

Part of the incoming PCI address is used as an offset from this starting address to

access the scatter-gather PTE. This PTE, together with the remaining least-

significant PCI address bits, forms the 21164 memory address.

Unused bits of Tn_BASE must be cleared because the hardware performs an OR operation for the

concatenation.

Table A–11 Direct-Mapped PCI Target Address Translation

Translated Address Source

W_MASK<31:20> Window Size T

_BASE

PCI Address

0000 0000 0000 1MB addr<32:20> addr<19:2>

0000 0000 0001 2MB addr<32:21> addr<20:2>

0000 0000 0011 4MB addr<32:22> addr<21:2>

0000 0000 0111 8MB addr<32:23> addr<22:2>

0000 0000 1111 16MB addr<32:24> addr<23:2>

0000 0001 1111 32MB addr<32:25> addr<24:2>

0000 0011 1111 64MB addr<32:26> addr<25:2>

0000 0111 1111 128MB addr<32:27> addr<26:2>

0000 1111 1111 256MB addr<32:28> addr<27:2>

0001 1111 1111 512MB addr<32:29> addr<28:2>

0011 1111 1111 1GB addr<32:30> addr<29:2>

0111 1111 1111 2GB addr<32:31> addr<30:2>

1111 1111 1111 4GB addr<32> addr<31:2>