CAN Bus CRC Adaptation for Higher Data Rate Reliability
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Solution Overview
Problem
Current CAN bus systems face limitations in data transmission reliability and rate, especially with increasing data demands in modern vehicles, as they are not adequately equipped to handle larger data quantities and varying latency requirements for systems like driving dynamics control and driver assistance systems.
Innovation Solution
The method modifies the CAN standard by using a modified polynomial for checksum calculation, allowing a variable CRC field size and data length, enabling parallel checksum calculations, and allowing for flexible data field sizes, bit length switching, and inclusion of stuff bits in CRC calculation to enhance error detection and increase data transmission rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the CAN standard protocol is used with fixed CRC field size and data length, then compatibility and ease of operation are maintained, but data transmission rate and flexibility are limited
Solution Approach 1:
The patent implements dynamic protocol adaptation by allowing the CRC field size and data length to vary based on transmission requirements. The system can switch between standard CAN mode (15-bit CRC, max 8 bytes data) and extended mode (up to 31-bit CRC, up to 128 bytes data), enabling the protocol to adapt its parameters dynamically rather than being fixed, thus resolving the contradiction between maintaining simplicity and increasing transmission capability.
Solution Approach 2:
The patent changes key protocol parameters including CRC field size (15, 21, 27, or 31 bits), data field length (1 to 128 bytes), and polynomial selection based on transmission needs. By making these parameters variable rather than fixed, the system can optimize for either speed or reliability depending on conditions, thereby increasing data transmission rate while maintaining compatibility through selective parameter usage.
2Reliability
If the CRC field size is increased to improve error detection for larger data quantities, then reliability is improved, but transmission time and complexity increase
Solution Approach 1:
The patent applies partial action by allowing the system to use only the necessary CRC size for each transmission based on data length and reliability requirements. Instead of always using the maximum 31-bit CRC which would ensure maximum reliability but increase transmission time, the system selectively applies 15-bit, 21-bit, 27-bit, or 31-bit CRC depending on the specific transmission needs, thus achieving adequate reliability without excessive time loss.
Solution Approach 2:
The system dynamically adjusts CRC field size based on the data field length and transmission requirements. For shorter data fields, a 15-bit or 21-bit CRC may suffice, while longer data fields benefit from 27-bit or 31-bit CRC. This dynamic adaptation ensures that error detection capability matches the actual risk level, preventing unnecessary time consumption on over-engineered error checking.
3Adaptability or versatility
If parallel checksum calculations are implemented to handle variable CRC sizes, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent segments the checksum calculation process into multiple parallel paths, each handling a specific CRC size (15-bit, 21-bit, 27-bit, 31-bit). Instead of implementing a single complex variable-size CRC calculator, the system divides the functionality into separate parallel calculation units, each optimized for a specific CRC size. This segmentation allows the controller to select and execute only the necessary calculation path, reducing actual complexity while maintaining high adaptability.
4Productivity
If variable data field sizes up to 128 bytes are allowed to increase data transmission capacity, then productivity is improved, but compatibility with standard CAN systems deteriorates
Solution Approach 1:
The patent implements a dual-mode system where extended CAN functionality is provided through a compatibility layer. Standard CAN controllers continue to operate with their native 15-bit CRC and 8-byte data field limits, while the extended CAN system uses up to 31-bit CRC and 128-byte data fields. The system copies the standard CAN protocol behavior when needed to ensure compatibility, while enabling extended capabilities when required, thus resolving the contradiction between increased capacity and maintained compatibility.
Data Source
AI summary
A method for serial data transmission in a bus system having at least two subscribed data processing units, the data processing units exchanging messages via the bus, the transmitted messages having a logical structure in accordance with the CAN standard ISO 11898-1, the logical structure including a start-of-frame bit, an arbitration field, a control field, a data field, a CRC field, an acknowledge field and an end-of-frame sequence, the control field including a data length code, which contains information regarding the length of the data field. The CRC field of the transmitted messages may have at least two different numbers of bits as a function of the content of the data length code.