Content addressable memory having prioritization of unoccupied entries
AssigneeCypress Semiconductor Corporation
InventorsStefan P. Sywyk, Eric H. Voelkel
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Abstract
According to one embodiment, a content addressable memory (CAM) (100) can include a number of CAM entries (102-0 to 102-n) and corresponding status stores (106-0 and 106-n). Match indications from the CAM entries (102-0 to 102-n) and status information from status stores (106-0 and 106-n) can be supplied to a switching circuit (108). Status information can indicate if an entry stores valid or invalid data. In one mode of operation, the switching circuit (108) can provide match indication values on a number of switch outputs (SW0 to SWn). In another mode of operation, the switching circuit (108) can provide status information on a number of switch outputs (SW0 to SWn).
Claims18
A content addressable memory (CAM), comprising:
- a plurality of entries that store data values, each entry generating a match indication in response to a comparison between a comparand value and its data value and including a plurality of CAM cells, at least one CAM cell of the entry storing a status indication associated with the entry;
- a the status indication associated with each entry indicates if the entry stores valid or invalid data;
- and
- a priority encoder that prioritizes match indications and status indications.
A method of operating a content addressable memory (CAM), comprising the steps of:
- storing data values in a number of entries;
- storing a status indication corresponding to each entry that indicates a valid or invalid status for the entry;
- in a compare mode, comparing a comparand value to data values and generating a number of match indications, and applying the match indications to a priority encoder, the comparand value including a status portion that is compared to the status indications corresponding to the data values;
- and
- in a find next free mode, applying the status indications to the priority encoder.
A content addressable memory (CAM), comprising:
- a plurality of entries that store data values for comparison to comparand values, each entry including status data that indicates if the entry stores valid data, and generating a match indication in response to a comparison between a comparand value and valid data, and each entry including a plurality of CAM cells, at least one of the CAM cells storing status information and providing status data;
- and
- a switch circuit that couples match indications to witch outputs in one mode, and couples status data to the switch outputs in another mode;
- and
- a priority encoder coupled to the switch outputs that prioritizes match indications in the one mode and prioritizes status data in the other mode.
The CAM of clam 12, wherein:
- the switch circuit includes a multiplexer circuit.
Dependencies are inferred from the claim text.