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4.2.2 B-Cache Tags
Many locations in memory space can map onto one index in the cache. To
identify which of these memory locations is currently stored in the B-cache,
a tag for each block is stored in the tag address RAMs. This tag together
with the B-cache index uniquely identifies the stored block. The tag ad-
dress is stored in the tag RAMs with odd parity. Figure 4-1 shows the
mapping of block address to B-cache index (used to address the cache
RAMs) and B-cache tag (stored to identify which block is valid at that ad-
dress). For comparison, Figure 4-2 and Figure 4-3 show the mapping for 1-
Mbyte and 16-Mbyte configurations.
Figure 4-1
Cache Index and Tag Mapping to Block Address (4MB)
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38
0
38
Figure 4-2
Cache Index and Tag Mapping to Block Address (1MB)
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Processor Byte Address
Tag<38:22>
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Processor Byte Address
0
38
Tag<38:20>
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22
B-Cache Index<21:6>
Wrap Order
BXB0826.AI
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B-Cache Index<19:6>
Wrap Order
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BXB0823.AI
Memory Subsystem 4-3
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