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Intel XScale® Core Developer's Manual
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
exact command.) Once enabled, any new lines allocated into the data cache will be locked down.
Note that the PLD instruction will 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.
Effect on Round Robin Replacement" on page 6-74
locked into the cache along with how the round-robin pointer is affected.
Figure 6-3.
Locked Line Effect on Round Robin Replacement
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
Lines are unlocked in the data cache by performing an unlock operation. See
"Register 9: Cache Lock Down" on page 7-90
the data cache.
Before locking, the programmer must ensure that no part of the target data range is already resident in
the cache. The core will not refetch such data, which will result 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.
74
Table 7-14, "Cache Lockdown Functions" on page 7-90
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
set 0
set 1
way 0
way 1
way 7
way 8
way 22
way 23
way 30
way 31
January, 2004
is an example of where lines of code may be
...
set 2
Figure
6-3.
for more information about locking and unlocking
for the
Figure 6-3, "Locked Line
set 31
Section 7.2.10,
Developer's Manual
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