PoC.cache.replacement_policyΒΆ

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Supported policies:

Abbr. Policies supported
RR round robin not yet
RAND random not yet
CLOCK clock algorithm not yet
LRU least recently used YES
LFU least frequently used not yet

Command thruth table:

TagAccess ReadWrite Invalidate Replace Command
0     0 None
1 0 0 0 TagHit and reading a cache line
1 1 0 0 TagHit and writing a cache line
1 0 1 0 TagHit and invalidate a cache line (while reading)
1 1 1 0 TagHit and invalidate a cache line (while writing)
0   0 1 Replace cache line

In a set-associative cache, each cache-set has its own instance of this component.

The input HitWay specifies the accessed way in a fully-associative or set-associative cache.

The output ReplaceWay identifies the way which will be replaced as next by a replace command. In a set-associative cache, this is the way in a specific cache set (see above).

Entity Declaration:

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entity cache_replacement_policy is
  generic (
    REPLACEMENT_POLICY : string   := "LRU";
    CACHE_WAYS         : positive := 32
  );
  port (
    Clock : in std_logic;
    Reset : in std_logic;

    -- replacement interface
    Replace    : in  std_logic;
    ReplaceWay : out std_logic_vector(log2ceilnz(CACHE_WAYS) - 1 downto 0);

    -- cacheline usage update interface
    TagAccess  : in std_logic;
    ReadWrite  : in std_logic;
    Invalidate : in std_logic;
    HitWay     : in std_logic_vector(log2ceilnz(CACHE_WAYS) - 1 downto 0)
  );
end entity;