SH7720 Datasheet, PDF (269/1524 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7700 Series

Section 5 Cache
5.3.2 Read Access
(1) Read Hit
In a read access, instructions and data are transferred from the cache to the CPU. The LRU is
updated to indicate that the hit way is the most recently hit way.
(2) Read Miss
An external bus cycle starts and the entry is updated. The way to be replaced is shown in table 5.4.
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 to the cache, the U bit is cleared to 0 and
the V bit is set to 1 to indicate that the hit way is the most recently hit way. When the U bit for the
entry which is to be replaced by entry updating 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. Transfer is in 16-byte units.
5.3.3 Prefetch Operation
(1) Prefetch Hit
The LRU is updated to indicate that the hit way is the most recently hit way. The other contents of
the cache are not changed. Instructions and data are not transferred from the cache to the CPU.
(2) Prefetch Miss
Instructions and data are not transferred from the cache to the CPU. The way that is to be replaced
is shown in table 5.3. The other operations are the same as those for a read miss.
5.3.4 Write Access
(1) 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 that has been written to is set to 1, and the LRU is
updated to indicate that the hit way is the most recently hit way. In write-through mode, the data is
written to the cache and an external memory write cycle is issued. The U bit of the entry that has
been written to is not updated, and the LRU is updated to indicate that the hit way is the most
recently hit way.
Rev. 3.00 Jan. 18, 2008 Page 207 of 1458
REJ09B0033-0300