Chapter 11
254 MIPS R4000 Microprocessor User's Manual
Accessing the Secondary Cache
Figure 11-7 shows the physical address (PA) index into the secondary
cache. The secondary cache ranges in size from 128 Kbytes to 4 Mbytes,
and the number of physical address bits used to index the cache depends
upon the cache size. For instance, PA(16:4) accesses the tags in a 128-Kbyte
secondary cache with 4-word lines; PA(21:5) accesses the tags in a 4-Mbyte
secondary cache with 8-word lines.
The processor always uses PA(35:17) from the secondary cache, regardless
of the S-cache size. This makes it important to initialize all secondary
cache tag address bits with a valid physical address, regardless of the size
of the S-cache.
Figure 11-7 Secondary Cache Data and Tag Organization
Tags
PA(16:n*) for 128 Kbyte
to
PA(21:n*) for 4 Mbyte
PA(16:n*)
to
PA(21:n*)
Data
ECC CS PIdx Tag
Data
Tag line
Data line
*n = 4 for 4-word lines
n = 5 for 8-word lines
n = 6 for 16-word lines
n = 7 for 32-word lines
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