CAM bit error recovery

• US 9,069,705 B2
• Filed: 02/26/2013
• Issued: 06/30/2015
• Est. Priority Date: 02/26/2013
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Manula, Brian Edward, Schanke, Morten, Wittosch, Robert W.
• Primary Examiner(s): Rizk, Sam
• Application Number:
  US13/777,546
• Publication Number:
  US 20140245092A1
• Time in Patent Office: 854 Days
• Field of Search: 714/763, 711/108, 365/49
• US Class Current: 1/1
• CPC Class Codes: G06F 11/1064 in cache or content addressable memories
• CPC Class Codes: G06F 11/1405 at machine instruction level

Abstract

A method for content addressable memory (CAM) error recovery that includes detecting an error in an entry of a CAM, identifying an address of the entry in the CAM, copying data from the address in the backup random access memory (RAM) into the entry of the CAM to obtain a corrected CAM, clearing a results (first in first out) FIFO structure based on detecting the error, performing, using the corrected CAM, a match request stored in a replay FIFO structure to obtain a revised result, and storing the revised result in the results FIFO structure.

Claims

1. A method for content addressable memory (CAM) error recovery, comprising:

detecting an error in an entry of a CAM;

identifying an address of the entry in the CAM;

copying data from the address in a backup random access memory (RAM) into the entry of the CAM to obtain a corrected CAM;

clearing a results (first in first out) FIFO structure based on detecting the error;

performing, using the corrected CAM, a match request stored in a replay FIFO structure to obtain a revised result; and

storing the revised result in the results FIFO structure.

2. The method of claim 1, further comprising:

receiving a CAM update;

identifying the address in the CAM from the CAM update to obtain an identified address; and

issuing the CAM update to the identified address in the CAM and the identified address in the backup RAM.

3. The method of claim 2, further comprising:

updating a parity bit of the entry in the CAM based on issuing the CAM update, wherein the error is detected using the parity bit.

4. The method of claim 1, further comprising:

receiving the match request;

storing the received match request in the replay FIFO structure;

issuing the match request to the CAM to obtain a result; and

storing the result in the results FIFO structure.

5. The method of claim 4, wherein the result is cleared from the result FIFO before elapse of an error time.

6. The method of claim 1, wherein the match request is received from a requesting module, and further comprising:

returning the revised result to the requesting module after an elapse of an error time.

7. The method of claim 6, wherein the error time is determined to elapse when the result is a next result to be returned from the result FIFO structure.

8. The method of claim 7, wherein a size of the result FIFO structure is calculated as a function of a first amount of time to detect the error in the CAM and clear the result FIFO structure, and a second amount of time to return an entry in the result FIFO structure.

9. The method of claim 1, further comprising:

after detecting the error and prior to copying data from the backup RAM, switching to a recovery mode from an operational mode;

halting incoming match requests and CAM updates based on being in the recovery mode; and

after performing match requests in the replay FIFO structure, switching from the recovery mode to the operational mode.

10. The method of claim 1, further comprising:

receiving a notification of the error by a master state machine; and

initiating, by the master state machine, a repair of the CAM.

11. A content addressable memory (CAM) system for error recovery, comprising:

a CAM comprising a plurality of entries for storing data;

a backup random access memory (RAM) operatively connected to the CAM, and for storing a copy of data stored in the plurality of entries of the CAM;

a replay first in first out (FIFO) structure operatively connected to the CAM, and for storing a plurality of match requests;

a results FIFO structure operatively connected to the CAM, and for storing a plurality of results of the plurality of match requests; and

a master state machine operatively connected to the CAM, the results FIFO structure, the replay FIFO structure, and the backup RAM, and configured to;

receive notification of an error in an entry of the plurality of entries,

initiate copying of data from the backup RAM into the entry of the CAM to obtain a corrected CAM,

clear the results FIFO structure based on detecting the error, and

initiate performing, using the corrected CAM and the replay FIFO structure, a match request of the plurality of match requests.

12. The CAM system of claim 11, wherein the backup RAM and CAM are configured to:

receive a CAM update; and

store the CAM update in a location specified by an address in the CAM update.

13. The CAM system of claim 11, wherein the CAM comprises:

a parity block comprising, for each entry of the plurality of entries, a parity bit and parity logic, wherein the parity logic is configured to detect the error in the corresponding entry of the plurality of entries using the parity bit.

14. The CAM system of claim 11, wherein the replay FIFO structure is configured to:

receive a copy of each incoming match requests received by the CAM;

store the copy of each incoming match requests received by the CAM; and

send, in order, the plurality of match requests stored in the replay FIFO structure to the CAM in response to notification from the master state machine.

15. The CAM system of claim 11, wherein the results FIFO is further configured to:

return the revised result to a requesting module after an elapse of an error time.

16. The CAM system of claim 11, wherein the master state machine comprises:

a mode bit for switching between operational mode and recovery mode, and

wherein the master state machine is further configured to;

after receiving notification of the error and prior to initiating copying of the data from the address, switch the mode bit to the recovery mode;

halting incoming match requests and CAM updates based on being in the recovery mode; and

match requests in the replay FIFO structure are performed, switch the mode bit to operational mode.

17. The CAM system of claim 11, further comprising:

a repair state machine operatively connected to the master state machine and configured to;

receive, from the master state machine, a notification to copy the data from the backup RAM; and

perform the copying of the data from the backup RAM based on the notification.

18. A chip comprising:

a content addressable memory (CAM) comprising a plurality of entries for storing data;

a backup random access memory (RAM) physically connected to the CAM, and for storing a copy of data stored in the plurality of entries of the CAM;

a replay first in first out (FIFO) structure physically connected to the CAM, and for storing a plurality of match requests;

a results FIFO structure physically connected to the CAM, and for storing a plurality of results of the plurality of match requests; and

a master state machine physically connected to the CAM, the results FIFO structure, the replay FIFO structure, and the backup RAM, and configured to;

receive notification of an error in an entry of the plurality of entries,

initiate copying of data from the backup RAM into the entry of the CAM to obtain a corrected CAM,

clear the results FIFO structure based on detecting the error, and

initiate performing, using the corrected CAM and the replay FIFO structure, a match request of the plurality of match requests.

19. The chip of claim 18, wherein the CAM comprises:

a parity block comprising, for each entry of the plurality of entries, a parity bit and parity logic, wherein the parity logic is configured to detect the error in the corresponding entry of the plurality of entries using the parity bit.

20. The chip of claim 18, further comprising:

a repair state machine operatively connected to the master state machine and configured to;

receive, from the master state machine, a notification to copy the data from the backup RAM; and

perform the copying of the data based on the notification.