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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262-004US
95
Intel XScale
®
Processor—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
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
9: Cache Lock Down” on page 105
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 XScale processor will not prefetch 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.
See
“Terminology and Conventions” on page 39
for a definition of coalescing.
The write buffer is always enabled which means stores to external memory will be
buffered. The K bit in the Auxiliary Control Register (CP15, register 1) is a global
enable/disable for allowing coalescing in the write buffer. When this bit disables
coalescing, no coalescing will occur regardless the value of the page attributes. If this
bit enables coalescing, the page attributes X, C, and B are examined to see if
coalescing is enabled for each region of memory.
All reads and writes to external memory occur in program order when coalescing is
disabled in the write buffer. If coalescing is enabled in the write buffer, writes may
occur out of program order to external memory. Program correctness is maintained in
this case by comparing all store requests with all the valid entries in the fill buffer.
Figure 12.
Locked Line Effect on Round-Robin Replacement
Notes:
1.
Set 0: 8 ways locked, 24 ways available for round robin replacement
2.
Set 1: 23 ways locked, 9 ways available for round robin replacement
3.
Set 2: 28 ways locked, only ways 28-31 available for replacement
4.
Set 31: all 32 ways available for round robin replacement
B4337-01
way 0
way 1
way 7
way 8
way 22
way 23
way 30
way 31
set 1
set 31
Lo
c
k
ed
set 0
Lo
c
k
ed
set 2
Lo
c
k
ed
...
..
.
..
.
..
.