Content addressable memory entry coding for error detection and correction

A content addressable memory comprising:

• lookup-data inputs receiving lookup data
• a plurality of entries, each entry including a plurality of entry groups that each provide a contribution to an associated hit indication of the entry, each entry group having associated storage bits storing an encoded comparison value, wherein the encoded comparison value of a particular entry group of a particular entry is decoded to produce match controls, the match controls being used to effect a comparison with a portion of the lookup data inputs to produce the contribution of the particular entry group to the associated hit indication of the particular entry;
• and
• a match information output summarizing the hit indications from one or more of the entries.

A content addressable memory comprising:

• lookup-data inputs receiving lookup data;
• write-data inputs receiving write data;
• a plurality of entries, each entry including a hit indication and a plurality of entry groups, each entry group including storage bits storing Error Detection And Correction (EDAC)-encoded comparison value information;
• a match information output summarizing the hit indications from at least some of the plurality of entries;
• and
• a data encoder encoding the write data to produce the EDAC-encoded comparison value information of each entry group.

An entry of a content addressable memory comprising:

• a plurality of storage bits holding a comparison value, the plurality of storage bits comprised of a plurality of groups of bits, each group of bits separately encoded;
• a lookup input for entry-level comparison with the comparison value, the lookup input having a number of bits associated with each of the groups of bits;
• a hit indication output indicating a hit when the lookup input corresponds with the comparison value, wherein the hit indication output is correct even when a correctable error is contained in the particular group of bits;
• and
• logic associated with a particular group of bits to, at least in part, perform a group-level comparison between the bits of the lookup input associated with the particular group of bits and a portion of the comparison value held in an encoded form in the particular group of bits, the group-level comparison being a sub-portion of the entry-level comparison.

An entry of a content addressable memory comprising:

• comparison value information;
• a lookup input for entry-level comparison with the comparison value information, the lookup input segregated into a plurality of lookup groups of bits;
• a hit indication output indicating a hit when the lookup input compares properly with the comparison value information;
• a plurality of entry groups, each entry group coupled to a corresponding lookup group, each entry group comprising a contribution to the hit indication output and a plurality of Error Detection And Correction (EDAC)-encoded storage bits, the storage bits among all entry groups holding the comparison value information of the entry;
• and
• means for determining the contribution to the hit indication output of each entry group.

A method for data lookup in a content addressable memory comprising:

• comparing a lookup-data input against one or more entries of the content addressable memory and generating a hit indication of the compared entry when comparison value information maintained in the compared entry agrees with the lookup-data input;
• summarizing the hit indications of each compared entry to produce a match indication output;
• wherein the comparing against a particular entry is done in parts by multiple entry groups that each process a number of bits of the lookup-data input, each entry group storing an encoded portion of the comparison value information for the particular entry;
• and
• wherein the encoded comparison value is compared with a portion of the lookup-data input using an error-correcting comparison to produce a contribution of a particular entry group to the hit indication for the compared entry.