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Section 7 Cache
Rev. 4.00 Sep. 14, 2005 Page 188 of 982
REJ09B0023-0400
7.3.2 Read
Access
Read Hit: In a read access, instructions and data are transferred from the cache to the CPU. LRU
is updated so that the hit way is the latest.
Read Miss: An external bus cycle starts and the entry is updated. The way replaced follows table
7.5. Entries are updated in 16-byte units. When the desired instruction or data that caused the miss
is loaded from external memory to the cache, the instruction or data is transferred to the CPU in
parallel with being loaded to the cache. When it is loaded in the cache, the U bit is cleared to 0 and
the V bit is set to 1. LRU is updated so that the replaced way becomes the latest. When the U bit
of the entry to be replaced by updating the entry in write-back mode is 1, the cache update cycle
starts after the entry is transferred to the write-back buffer. After the cache completes its update
cycle, the write-back buffer writes the entry back to the memory. The write-back unit is 16 bytes.
7.3.3 Prefetch
Operation
Prefetch Hit: LRU is updated so that the hit way becomes the latest. The contents in other caches
are not modified. No instructions or data is transferred to the CPU.
Prefetch Miss: No instructions or data is transferred to the CPU. The way to be replaced follows
table 7.4. Other operations are the same in case of read miss.
7.3.4 Write
Access
Write Hit: In a write access in write-back mode, the data is written to the cache and no external
memory write cycle is issued. The U bit of the entry written is set to 1 and LRU is updated so that
the hit way becomes the latest. In write-through mode, the data is written to the cache and an
external memory write cycle is issued. The U bit of the written entry is not updated and LRU is
updated so that the replaced way becomes the latest.
Write Miss: In write-back mode, an external bus cycle starts when a write miss occurs, and the
entry is updated. The way to be replaced follows table 7.5. When the U bit of the entry to be
replaced is 1, the cache update cycle starts after the entry is transferred to the write-back buffer.
The write-back unit is 16 bytes. Data is written to the cache and the U bit is set to 1. V bit is set to
1. LRU is updated so that the replaced way becomes the latest. After the cache completes its
update cycle, the write-back buffer writes the entry back to the memory. In write-through mode,
no write to cache occurs in a write miss; the write is only to the external memory.
Summary of Contents for HD6417641
Page 2: ...Rev 4 00 Sep 14 2005 Page ii of l...
Page 7: ...Rev 4 00 Sep 14 2005 Page vii of l...
Page 11: ...Rev 4 00 Sep 14 2005 Page xi of l USB Universal serial bus WDT Watch dog timer...
Page 12: ...Rev 4 00 Sep 14 2005 Page xii of l...
Page 28: ...Rev 4 00 Sep 14 2005 Page xxviii of l...
Page 204: ...Section 4 Clock Pulse Generator CPG Rev 4 00 Sep 14 2005 Page 154 of 982 REJ09B0023 0400...
Page 212: ...Section 5 Watchdog Timer WDT Rev 4 00 Sep 14 2005 Page 162 of 982 REJ09B0023 0400...
Page 228: ...Section 6 Power Down Modes Rev 4 00 Sep 14 2005 Page 178 of 982 REJ09B0023 0400...
Page 246: ...Section 8 X Y Memory Rev 4 00 Sep 14 2005 Page 196 of 982 REJ09B0023 0400...
Page 318: ...Section 11 User Break Controller UBC Rev 4 00 Sep 14 2005 Page 268 of 982 REJ09B0023 0400...
Page 454: ...Section 12 Bus State Controller BSC Rev 4 00 Sep 14 2005 Page 404 of 982 REJ09B0023 0400...
Page 504: ...Section 14 U Memory Rev 4 00 Sep 14 2005 Page 454 of 982 REJ09B0023 0400...
Page 566: ...Section 17 Compare Match Timer CMT Rev 4 00 Sep 14 2005 Page 516 of 982 REJ09B0023 0400...
Page 868: ...Section 21 A D Converter Rev 4 00 Sep 14 2005 Page 818 of 982 REJ09B0023 0400...
Page 914: ...Section 23 I O Ports Rev 4 00 Sep 14 2005 Page 864 of 982 REJ09B0023 0400...
Page 956: ...Section 24 List of Registers Rev 4 00 Sep 14 2005 Page 906 of 982 REJ09B0023 0400...
Page 1016: ...Section 25 Electrical Characteristics Rev 4 00 Sep 14 2005 Page 966 of 982 REJ09B0023 0400...
Page 1024: ...Appendix Rev 4 00 Sep 14 2005 Page 974 of 982 REJ09B0023 0400...
Page 1032: ...Rev 4 00 Sep 14 2005 Page 982 of 982 REJ09B0023 0400 X X Y data addressing 52 X Y memory 193...
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