CRC PROTECTION OF DATA STORED IN XOR BUFFER

• US 20100306634A1
• Filed: 05/28/2009
• Published: 12/02/2010
• Est. Priority Date: 05/28/2009
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Fujitsu Limited
• Inventors: Lincoln, Bradford C.
• Granted Patent: US 8,266,499 B2
• Time in Patent Office: Days
• US Class Current: 714/807
• CPC Class Codes: G06F 7/02 Comparing digital values G06F7/06, G06F7/22, G06F7/38 take precedence
• CPC Class Codes: G09C 1/00 Apparatus or methods whereby a given sequence of signs, e.g. an intelligible text, is transformed into an unintelligible sequence of signs by transposing the signs or groups of signs or by replacing them by others according to a predetermined system cryptographic typewriters G09C3/00
• CPC Class Codes: G11B 20/1833 by adding special lists or symbols to the coded information G11B20/1806, G11B20/1866 take precedence
• CPC Class Codes: G11B 2020/1843 using a cyclic redundancy check [CRC]
• CPC Class Codes: G11B 2220/2516 Hard disks
• CPC Class Codes: G11B 2220/415 Redundant array of inexpensive disks [RAID] systems

Abstract

An XOR unit is provided in a hard disk controller for calculating an XOR of two operands stored in a buffer memory. The XOR unit includes an XOR calculator for calculating the XOR of the operands and a CRC of the XOR resulting from the calculation. An XOR buffer is also included in the XOR unit for storing the XOR result and the CRC of the XOR result, and a CRC calculator for calculating a CRC of the XOR result stored in the XOR buffer. The CRC calculated by the CRC calculator is compared with the CRC of the XOR result stored in the CRC buffer to determine whether the XOR result has been corrupted in the XOR buffer. The XOR result stored in the XOR buffer is determined to be corrupted if the CRC calculated by the CRC calculator and the CRC stored in the XOR buffer do not match.

Claims

1. An XOR unit in a hard disk controller for calculating an XOR of two operands stored in a buffer memory, comprising:

an XOR calculator for calculating the XOR of the operands and a first CRC of an XOR result calculated by the XOR calculator;

an XOR buffer for storing the XOR result and the first CRC of the XOR result;

a second CRC calculator for calculating a second CRC of the XOR result stored in the XOR buffer;

wherein the second CRC of the XOR result calculated by the second CRC calculator is compared with the first CRC of the XOR result stored in the CRC buffer to determine whether the XOR result has been corrupted in the XOR buffer, the XOR result stored in the XOR buffer being determined to be corrupted if the second CRC of the XOR result does not match the first CRC of the XOR result.

2. The XOR unit as defined in claim 1, further comprising:

a first CRC calculator for calculating a CRC of each operand used in calculating the XOR result; and

a correction term calculator for calculating a correction;

wherein the XOR calculator calculates the first CRC of the XOR result from the CRC of each operand and the correction term.

3. The XOR unit as defined in claim 2, wherein the CRC of each operand is calculated as follows:

CRC(D)=(x̂

N*D(x)|x̂

K*S(x))mod G(x),

where D(x) is a data polynomial, K is the degree of D(x), G(x) is a generator polynomial, N is a degree of G(x), and S(x) is a CRC initial value.

4. The XOR unit as defined in claim 3, wherein the CRC correction term is calculated as follows:

C(x)=(x̂

K*S(x))mod G(x),

where K is a total number of bits in all data segments in a data sector, G(x) is the generator polynomial, and S(x) is the CRC initial value.

5. The XOR unit as defined in claim 4, wherein the first CRC of the XOR result is calculated as follows:

6. The XOR unit as defined in claim 2, wherein the first CRC calculator comprises:

an update function unit for calculating a current CRC of the operands;

a register for storing the CRC calculated in the update function unit; and

a comparator for comparing the CRC stored in the register with the CRC of each of the operands.

7. The XOR unit as defined in claim 6, wherein the update function units calculates the current CRC of the operands as follows:

U(X)=(x̂

N*Dn(x)⊕

x̂

Kw*Sn(x))mod G(x),

where Dn(x) is a word of input data, n is the word index, Kw is a width of the word and Sn(x) is a current value stored in the register.

8. The XOR unit as defined in claim 2, wherein the correction term calculator comprises:

an update function unit for calculating a current correction term; and

a register for storing the correction term calculated in the update function unit.

9. The XOR unit as defined in claim 8, wherein the update function units calculates the current CRC as follows:

C(x)=(x̂

K*Sn(x))mod G(x),

where K is a total number of bits in all data segments in a data sector, G(x) is a generator polynomial, and S(x) is an initial value.

10. The XOR unit as defined in claim 1, wherein the second CRC calculator comprises:

an update function unit for calculating the second CRC of the XOR result;

a register for storing the second CRC calculated in the update function unit; and

a comparator for comparing the second CRC stored in the register with the first CRC of the XOR result.

11. The XOR unit as defined in claim 10, wherein the second CRC of the XOR result is calculated as follow:

CRC(R)=(x̂

N*R(x)⊕

x̂

K*S(x))mod G(x),

where R(x) is the XOR result, K is a total number of bits in all data segments in a data sector, G(x) is a generator polynomial, N is a degree of G(x), and S(x) is a CRC initial value.

12. A method for checking for corruption in an XOR result calculated from an XOR operation of two operands and stored in a buffer, the method comprising:

calculating the XOR result of the two operands;

calculating a first CRC of the XOR result;

storing the XOR result and the first CRC of the XOR result in the buffer;

calculating a second CRC of the XOR result stored in the XOR buffer;

comparing the second CRC of the XOR result with the first CRC of the XOR result stored in the buffer to determine whether the XOR result has been corrupted in the buffer, the XOR result stored in the buffer being determined to be corrupted if the second CRC of the XOR result does not match the first CRC of the XOR result.

13. The method as defined in claim 12, wherein the first CRC of the XOR result is calculated from a CRC of each operand and a correction term.

14. The method as defined in claim 13, wherein the CRC of each operand is calculated as follows:

CRC(D)=(x̂

N*D(x)⊕

x̂

K*S(x))mod G(x),

where D(x) is a data polynomial, K is the degree of D(x), G(x) is a generator polynomial, N is a degree of G(x), and S(x) is a CRC initial value.

15. The method as defined in claim 14, wherein the correction term is calculated as follows:

C(x)=(x̂

K*S(x))mod G(x),

where K is the total number of bits in all data segments in a data sector, G(x) is the generator polynomial, and S(x) is the CRC initial value.

16. The method as defined in claim 15, wherein the first CRC of the XOR result is calculated as follows:

17. The method as defined in claim 12, wherein the second CRC of the XOR result is calculated as follow:

CRC(R)=(x̂

N*R(x)⊕

x̂

K*S(x))mod G(x),

where R(x) is the XOR result, K is a total number of bits in all data segments in a data sector, G(x) is a generator polynomial, N is a degree of G(x), and S(x) is a CRC initial value.