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Developer’s Manual March, 2003 6-15
Intel
®
80200 Processor based on Intel
®
XScale
™
Microarchitecture
Data Cache
Tags can be locked into the data cache by enabling the data cache lock mode bit located in
coprocessor 15, register 9. (See Table 7-14, “Cache Lockdown Functions” on page 7-14 for the
exact command.) Once enabled, any new lines allocated into the data cache are locked down.
Note that the PLD instruction does not affect the cache contents if it encounters an error while
executing. For this reason, system software should ensure the memory address used in the PLD is
correct. If this cannot be ascertained, replace the PLD with a LDR instruction that targets a scratch
register.
Lines are locked into a set starting at way0 and may progress up to way 27; which set a line gets
locked into depends on the set index of the virtual address of the request. Figure 6-3, “Locked Line
Effect on Round Robin Replacement” on page 6-15 is an example of where lines of code may be
locked into the cache along with how the round-robin pointer is affected.
Software can lock down data located at different memory locations. This may cause some sets to
have more locked lines than others as shown in Figure 6-3.
Lines are unlocked in the data cache by performing an unlock operation. See Section 7.2.10,
“Register 9: Cache Lock Down” on page 7-14 for more information about locking and unlocking
the data cache.
Before locking, the programmer must ensure that no part of the target data range is already resident
in the cache. The Intel
®
80200 processor does not refetch such data, which results in it not being
locked into the cache. If there is any doubt as to the location of the targeted memory data, the cache
should be cleaned and invalidated to prevent this scenario. If the cache contains a locked region
which the programmer wishes to lock again, then the cache must be unlocked before being cleaned
and invalidated.
Figure 6-3. Locked Line Effect on Round Robin Replacement
way 0
way 1
way 7
way 8
way 22
way 23
way 30
way 31
set 1
set 31
Locked
set 0
Locked
set 2
Locked
...
...
......
set 0: 8 ways locked, 24 ways available for round robin replacement
set 1: 23 ways locked, 9 ways available for round robin replacement
set 2: 28 ways locked, only ways 28-31 available for replacement
set 31: all 32 ways available for round robin replacement