Section 8 Caches
Rev.1.00 Dec. 13, 2005 Page 211 of 1286
REJ09B0158-0100
8.3.4 Write-Back
Buffer
In order to give priority to data reads to the cache and improve performance, this LSI has a write-
back buffer which holds the relevant cache entry when it becomes necessary to purge a dirty cache
entry into external memory as the result of a cache miss. The write-back buffer contains one cache
line of data and the physical address of the purge destination.
LW7
Physical address bits [28:5]
LW6
LW5
LW4
LW3
LW2
LW1
LW0
Figure 8.3 Configuration of Write-Back Buffer
8.3.5 Write-Through
Buffer
This LSI has a 64-bit buffer for holding write data when writing data in write-through mode or
writing to a non-cacheable area. This allows the CPU to proceed to the next operation as soon as
the write to the write-through buffer is completed, without waiting for completion of the write to
external memory.
Physical address bits [28:0]
LW1
LW0
Figure 8.4 Configuration of Write-Through Buffer
8.3.6
OC Two-Way Mode
When the OC2W bit in RAMCR is set to 1, OC two-way mode which only uses way 0 and way 1
in the OC is entered. Thus, power consumption can be reduced. In this mode, only way 0 and way
1 are used even if a memory-mapped OC access is made.
The OC2W bit should be modified by a program in the P2 area. At that time, if the valid line has
already been recorded in the OC, data should be written back by software, if necessary, 1 should
be written to the OCI bit in CCR, and all entries in the OC should be invalid before modifying the
OC2W bit.
Содержание SH7780 Series
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