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46 Hardware Reference Manual
Intel
®
IXP2800 Network Processor
Technical Description
Note: The State bits are data associated with the entry. The use is only by software. There is no
implication of ownership of the entry by any Context. The State bits hardware function is:
• the value is set by software (at the time the entry is loaded, or changed in an already loaded
entry).
• its value is read out on a lookup that hits, and used as part of the status written into the
destination register.
• its value can be read out separately (normally only used for diagnostic or debug).
The LRU (Least Recently Used) Logic maintains a time-ordered list of CAM entry usage. When an
entry is loaded, or matches on a lookup, it is marked as MRU (Most Recently Used). Note that a
lookup that misses does not modify the LRU list.
The CAM is loaded by instruction:
CAM_Write[entry_reg, source_reg, state_value]
The value in the register specified by source_reg is put into the Tag field of the entry specified by
entry_reg. The value for the State bits of the entry is specified in the instruction as state_value.
Figure 7. CAM Block Diagram
A9354-01
Status
and
LRU
Logic
Tag
Lookup Value
(from A port)
State
Match
Match
Match
Tag State
Tag State
Tag State
Match
Lookup Status
(to Dest Req)
State Status Entry Number
0000 Miss 0 LRU Entry
State Hit 1 Hit Entry