HD6417618A datasheet(82/646 Pages) RENESAS

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Section 3 Cache

Rev. 6.00 Jun. 12, 2007 Page 50 of 610

REJ09B0131-0600

Address Array: The V bit indicates whether or not the entry data is valid. When the V bit is 1,

data is valid; when 0, data is not valid. The U bit indicates whether or not the entry has been

written to in write-back mode. When the U bit is 1, the entry has been written to; when 0, it has

not. The tag address is composed of 22 bits (address bits 31 to 10) used for comparison during

cache searches.

In this LSI, the upper three bits of 32 address bits are used as shadow bits (see section 7, Bus State

Controller (BSC)), therefore, the upper three bits of the tag address are cleared to 0.

The V and U bits are initialized to 0 by a power-on reset. The tag address is not initialized by a

power-on reset.

Data Array: Holds 16-byte instruction and data. Entries are registered in the cache in line units

(16 bytes). The data array is not initialized by a power-on reset.

LRU: With the 4-way set associative system, up to four instructions or data with the same entry

address can be registered in the cache. When an entry is registered, LRU shows which of the four

ways it is registered in. There are six LRU bits, controlled by hardware. The least-recently-used

(LRU) algorithm is used to select the way.

When a cache miss occurs, six LRU bits indicate the way to be replaced. If a bit pattern other than

those listed in table 3.1 is set in the LRU bits by software, the cache will not function correctly.

When changing the LRU bits by software, set one of the patterns listed in table 3.1.

The LRU bits are initialized to 000000 by a power-on reset.

Table 3.1

LRU and Way to be Replaced

LRU (Bits 5 to 0)

Way to be Replaced

000000, 000100, 010100, 100000, 110000, 110100

000001, 000011, 001011, 100001, 101001, 101011

000110, 000111, 001111, 010110, 011110, 011111

111000, 111001, 111011, 111100, 111110, 111111

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