A–40
System Address Space
Scatter-Gather TLB
1.15 Scatter-Gather TLB
An eight-entry translation lookaside buffer (TLB) is provided in the 21174 for scat-
ter-gather map entries. The TLB is a fully associative cache and holds the eight
most-recent scatter-gather map lookup PTEs. Four of these entries can be locked to
prevent their being displaced by the hardware TLB-miss handler. Each of the eight
TLB entries holds a PCI address for the tag and four consecutive 8KB 21164 page
addresses as the TLB data, as shown in Figure 1–20.
1
Unused bits of the Translated Base Register must be zero for correct operation.
0000 0001 1111
32KB
Translated Base<33:15> : ad<24:13>
0000 0011 1111
64KB
Translated Base<33:16> : ad<25:13>
0000 0111 1111
128KB
Translated Base<33:17> : ad<26:13>
0000 1111 1111
256KB
Translated Base<33:18> : ad<27:13>
0001 1111 1111
512KB
Translated Base<33:19> : ad<28:13>
0011 1111 1111
1MB
Translated Base<33:20> : ad<29:13>
0111 1111 1111
2MB
Translated Base<33:21> : ad<30:13>
1111 1111 1111
4MB
Translated Base<33:22> : ad<31:13>
Table A–14 Scatter-Gather Mapped PCI Target Address Translation
(Sheet 2 of 2)
W_MASK<31:20>
Size of SG
Map Table
Translated Address <32:2>