Serial Data Communication - CAN Memory Error Detection Methods

• US 20070038917A1
• Filed: 07/27/2006
• Published: 02/15/2007
• Est. Priority Date: 07/29/2005
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Thomas, James, Forest, Thomas, Katrak, Kerfegar
• Granted Patent: US 7,882,424 B2
• Time in Patent Office: Days
• US Class Current: 714/758
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 2001/0094 Bus

Abstract

A method is provided for formatting a message, with a first plurality of bits forming a data component, and a second plurality of bits forming a reserved component, for transmission in a vehicle. The method comprises the steps of calculating an initial checksum from the data component, calculating a revised checksum at least from the initial checksum, and storing the revised checksum in the reserved component. The number of bits in the reserved component is less than the number of bits in the data component.

Claims

1. A method of formatting a message for transmission in a vehicle, the message comprising a first plurality of bits forming a data component, and a second plurality of bits forming a reserved component, the method comprising the steps of:

calculating an initial checksum from the data component;

calculating a revised checksum at least from the initial checksum; and

storing the revised checksum in the reserved component, wherein the number of bits in the reserved component is less than the number of bits in the data component.

2. The method of claim 1, wherein the message further comprises a third plurality of bits forming an identifier component, and further comprising the step of:

generating at least one integer value representative of the identifier component; and

wherein the step of calculating the revised checksum comprises calculating the revised checksum at least from the initial checksum and the at least one integer value.

3. The method of claim 2, wherein the at least one integer value is generated so that an increase in the value of the identifier component results in an increase in the value of the at least one integer value.

4. The method of claim 3, wherein the at least one integer value is generated by dividing an initial value of the identifier component by a specified divider, so that when this division occurs the integer value will always be a distinct and unique integer value.

5. The method of claim 1, wherein the initial checksum is calculated as a bytewise sum of the plurality of bytes forming the data component.

6. The method of claim 1, wherein the revised checksum is inversely related to the initial checksum.

7. The method of claim 6, wherein the step of calculating the revised checksum comprises:

subtracting the initial checksum from a specified value, thereby calculating the revised checksum

8. The method of claim 2, wherein the step of calculating the revised checksum comprises:

adding together the at least one integer value and the initial checksum, thereby calculating an intermediate checksum; and

subtracting the intermediate checksum from a specified value, thereby calculating the revised checksum.

9. The method of claim 8, wherein:

the initial checksum includes a specific number of bits; and

the specified value is the maximum checksum number for the specific number of bits, minus one.

10. The method of claim 1, wherein the ratio of the number of bits in the reserved component to the number of bits in the data component is less than or equal to 1:

2.

11. The method of claim 10, wherein the ratio of the number of bits in the reserved component to the number of bits in the data component is less than or equal to 1:

4.

12. A method of formatting a message for transmission in a vehicle, the message comprising a plurality of data bytes, each data byte comprising a plurality of data bits and a reserved bit, the reserved bit adjacent to a preceding data bit, and a reserved data byte, the method comprising the steps of:

calculating an inverted value of the preceding data bit of each data byte;

storing the inverted value of the preceding data bit of each data byte in the reserved bit of such data byte;

calculating a checksum from the plurality of data bytes; and

storing the checksum in the reserved data byte of the message.

13. The method of claim 12, wherein the checksum is an exclusive or checksum calculated from the plurality of data bytes.

14. A memory for storing data for access by an application program being executed on a data processing system, comprising:

a data structure stored in the memory, the data structure including information resident in a database used by the application program and including;

a data object comprising a plurality of data bits;

an identifier object comprising a plurality of identifier bits capable of being represented by at least one integer value; and

a checksum object comprising a plurality of checksum bits reflecting a checksum of the plurality of data bits from the data object with the at least one integer value representing the plurality of identifier bits from the identifier object, and wherein the number of checksum bits is less than the number of data bits.

15. The memory of claim 14, wherein the at least one integer value is generated by dividing an initial value of the identifier component by a specified divider, such that when this division occurs the integer value will always be a distinct and unique integer value, and such that an increase in the value of the identifier component results in an increase in the value of the at least one integer value.

16. The memory of claim 14, wherein the plurality of checksum bits in the checksum object reflect at least a checksum comprising a bytewise sum of the plurality of data bytes.

17. The method of claim 14, wherein the revised checksum is inversely related to the initial checksum and the at least one integer value

18. The memory of claim 17, wherein the plurality of checksum bits in the checksum object reflect the subtraction of the checksum and the at least one integer value from a specified value.

19. The memory of claim 18, wherein:

the checksum includes a specific number of bits; and

the specified value is the maximum checksum number for the specific number of bits.

20. The memory of claim 19, wherein the ratio of the number of checksum bits to the number of data bits is less than or equal to 1:

2.