Apparatus and method for merging data blocks with error correction code protection

• US 7,797,609 B2
• Filed: 08/19/2004
• Issued: 09/14/2010
• Est. Priority Date: 08/19/2004
• Status: Active Grant

• Current Assignee: Unisys Corporation
• Original Assignee: Unisys Corporation
• Inventors: Neuman, Paul S.
• Primary Examiner(s): Alphonse; Fritz
• Application Number:
  US10/922,206
• Publication Number:
  US 20090313526A1
• Time in Patent Office: 2,217 Days
• Field of Search: 714/758, 714/763, 714/764, 714/768, 714/48, 714/52, 714/718
• US Class Current: 714/758
• CPC Class Codes: G06F 11/10 Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's

Abstract

An apparatus and method for selectively deriving Error Correction Codes (ECCs) or other data integrity information for integration into merged data blocks. First data is merged into second data that is error-protected using an ECC generated by a coding algorithm. Bytes or other data units are identified in the first data to be merged into the second data. It is determined whether each of the check bits of the ECC will differ from its original state in response to merging the first and second data. The check bits of the ECC that have been determined to differ from their respective original states are modified to create a “merged ECC.” The resulting data block includes the merged data and the merged ECC.

Claims

1. An apparatus having a computer-readable medium encoded with instruction executed within the apparatus for merging a first data block including first data, and a second data block including second data and an original Error Correction Code (ECC) having a plurality of ECC check bits, the apparatus comprising:

a data unit enable module to identify data units of the first data to be merged into corresponding data units of the second data;

a data merge module arranged to merge the identified data units of the first data into the corresponding data units of the second data to create merged data; and

a plurality of check bit generation modules each comprising means for determining whether a state of a respective one of the ECC check bits differs from its original state in the original ECC in response to merging the identified data units, and for establishing a respective revised ECC check bit based on the determination, wherein the respective revised ECC check bits from the plurality of check bit generation modules collectively provide a merged ECC for the merged data.

2. The apparatus as in claim 1, wherein each of the check bit generation modules respectively comprises an output to provide its respective revised ECC check bit, and wherein the outputs from each of the check bit generation modules collectively provides the merged ECC.

3. The apparatus as in claim 1, wherein the means for establishing a revised ECC check bit based on the determination comprise means for changing the state of the respective one of the ECC check bits if it is determined that the respective one of the ECC check bits differs from its original state in the original ECC as a result of the merging of the identified data units.

4. The apparatus as in claim 1, wherein the means for determining comprise means for identifying differences in corresponding data bits, as a function of a coding algorithm used to generate the original ECC, for each data unit of the first and second data.

5. The apparatus as in claim 4, wherein the means for identifying differences in corresponding data bits comprise a first stage of exclusive-OR modules to identify the differences in corresponding data bits.

6. The apparatus as in claim 4, wherein the means for determining further comprise:

a plurality of gates each coupled to the first state of exclusive-OR modules to enable passage of only the identified differences in corresponding data bits from the data units identified by the data unit enable module; and

a second stage exclusive-OR module coupled to the plurality of gates to receive the identified differences that have been passed by the plurality of gates, and to generate a check bit difference indicator in response thereto.

7. The apparatus as in claim 6, wherein the means for determining further comprise an output gate coupled to the second stage exclusive-OR and coupled to receive a respective one of the check bits from the original ECC, and to establish the respective revised ECC check bit based on the check bit difference indicator.

8. The apparatus as in claim 7, wherein the output gate comprises an exclusive-OR gate coupled to the second stage exclusive-OR and coupled to receive the respective one of the check bits from the original ECC, wherein the output gate is configured to toggle the respective one of the check bits from the original ECC to establish the respective revised ECC check bit if the check bit difference indicator indicates an odd number of the identified differences that have been passed by the plurality of gates.

9. The apparatus as in claim 6, wherein each of the plurality of gates is coupled to the data unit enable module to respectively receive one of a plurality of data unit enable signals indicative of whether passage of the identified differences in corresponding data bits is enabled.

10. The apparatus as in claim 1, wherein the data unit enable module comprises a register storing a plurality of enable bits, each enable bit corresponding to one of the data units to identify the data units of the first data to be merged into corresponding data units of the second data.

11. An apparatus having a computer-readable medium encoded with instruction executed within the apparatus for merging a first data block including first data, and a second data block including second data and an original Error Correction Code (ECC) having a plurality of ECC check bits, the apparatus comprising:

merging means for merging one or more data units of the first data into corresponding data units of the second data to create merged data;

determining means for determining whether one or more of the check bits of the original ECC will change as a result of the merging of the one or more data units of the first data into the second data; and

modifying means coupled to the determining means for modifying one or more of the check bits of the original ECC to produce a modified ECC for the merged data, in response to a determination by the determining means that a corresponding one or more of the check bits of the original ECC will change.

12. The apparatus as in claim 11, wherein the determining means comprises comparing means for comparing corresponding data bits of the first and second data on a data unit basis and as a function of a coding algorithm used to generate the original ECC, and for identifying each of the check bits that will change.

13. The apparatus as in claim 12, wherein the modifying means comprises means for toggling a state of the check bits that have been identified to change by the comparing means.

14. A method having a computer-readable medium encoded with instruction executed within a programmable computer for merging first data of a first data block into second data of a second data block, the second data block including a plurality of check bits generated according to a coding algorithm and forming an Error Correction Code (ECC) for the second data, the method comprising:

specifying one or more data units of the second data to be replaced by a corresponding one or more data units of the first data;

determining, as a function of the coding algorithm, whether each of the check bits of the ECC will differ from its respective original state upon replacing the specified data units of the second data;

modifying the check bits of the ECC that have been determined to differ from their respective original states to create a merged ECC;

replacing the specified data units of the second data with the corresponding one or more data units of the first data to create merged data; and

creating a resultant data block including the merged data and the merged ECC.

15. The method of claim 14, wherein specifying one or more data units comprises providing a plurality of enable bits, one for each of the data units of the second data, and asserting a respective one of the enable bits for each of the one or more data units of the second data to be replaced by a corresponding one or more data units of the first data.

16. The method of claim 14, wherein determining whether each of the check bits of the ECC will differ from its respective original state comprises:

for each of the check bits, comparing a respective subset of corresponding data bits of the first and second data as dictated by the coding algorithm, and in response providing respective data unit change indications; and

for each of the check bits, generating a check bit change indication based on the data unit change indications associated with the data units of the second data that are specified to be replaced, wherein the check bit change indication indicates whether the respective one of the check bits will differ from its respective original state upon replacing the specified data units of the second data.

17. The method of claim 16, wherein generating a check bit change indication comprises providing a affirmative check bit change indication indicating a difference of the respective check bit from its respective original state if an odd number of data unit change indications have occurred.

18. The method of claim 17, wherein modifying the check bits of the ECC that have been determined to differ from their respective original states comprises changing the original state of the respective check bit in response to receiving an affirmative check bit change indication.

19. The method of claim 16, wherein generating a check bit change indication comprises providing a negative check bit change indication indicating no difference of the respective check bit from its respective original state if an even number of data unit change indications have occurred.

20. The method of claim 16, further comprising, for each of the check bits, disregarding the data unit change indications associated with data units of the second data that are not specified to be replaced.

21. An apparatus having a computer-readable medium encoded with instruction executed within the apparatus for updating one or more check bits of an Error Correction Code (ECC) associated with reference data, in response to merging one or more data units of modifying data with the reference data, comprising:

a data unit enable module configured to store a plurality of enable bits, one for each of a first number of data units associated with the reference data, wherein the enable bits include one or more active enable bits identifying data units of the modifying data to be merged with the reference data;

a plurality of check bit generation modules, one for each of the check bits of the ECC associated with the reference data, wherein each of the plurality of check bit generation modules comprises;

a first stage array coupled to receive a set of corresponding data bits of the modifying data and the reference data according to a coding algorithm used to generate the ECC of the reference data, and to output a second number of change indications each indicating whether the merging of the one or more data units of modifying data with the reference data for a respective one of the first number of data units warrants a change in the check bit;

a gating array coupled to the first stage array to receive the second number of change indications and coupled to the data unit enable module to receive the plurality of enable bits, and arranged to pass the change indications associated with the active enable bits;

a second stage array coupled to the gating array to receive the change indications passed by the gating array, and arranged to generate a collective change indication; and

a third stage array coupled to the second stage array to receive the collective change indication and coupled to receive a corresponding one of the check bits of the ECC associated with the reference data, and arranged to modify the corresponding one of the check bits of the ECC based on the collective change indication.