LIN Slave Node Budget Calculation Using Sync Byte Timing
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Solution Overview
Problem
Current methods for calculating message time budgets in Local Interconnect Networks (LIN) result in inaccurate calculations, leading to improper rejection of valid messages due to the lack of precise timing in slave nodes without expensive crystals or resonators, causing errors in message transmission timing.
Innovation Solution
A method that calculates the message time budget by measuring the bit times for the sync byte and applying shift operations to determine both header and data budgets separately, ensuring accurate validation of message reception within the allotted time, thereby reducing improper message rejections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If slave nodes use a single bit time measurement from the SYNC byte to calculate message budget, then the calculation method is simple, but the measurement precision is insufficient leading to improper message rejection
Solution Approach 1:
The patent divides the message reception verification into two separate budget calculations: header budget and data budget. The header budget is calculated using the single bit time measurement from the SYNC byte, while the data budget is calculated by multiplying the measured bit time by the number of data bytes. This segmentation allows each part to use the most appropriate calculation method, improving overall accuracy without significantly increasing complexity.
Solution Approach 2:
The patent changes the calculation parameter from a single fixed budget value to two separate budget values (header budget and data budget) with different calculation methods. The header budget uses the 140% multiplier on measured bit time, while the data budget uses direct multiplication of bit time by data byte count. This parameter change resolves the contradiction by applying different precision levels to different message portions.
2Ease of manufacture
If slave nodes do not use expensive crystals or resonators for timing, then the device cost is reduced, but the timing accuracy deteriorates causing budget calculation errors
Solution Approach 1:
The patent applies partial action by using the inexpensive bit time measurement from the SYNC byte only for the header budget calculation, while applying a more precise calculation method (direct multiplication by data byte count) for the data portion. This partial application of different precision levels achieves acceptable overall accuracy without requiring expensive timing components throughout the entire system.
Solution Approach 2:
The patent changes the timing verification parameter from a single budget value to two separate budget values with different calculation methodologies. This parameter change allows the system to tolerate the imprecision of low-cost timing components in the header verification while maintaining adequate accuracy in the data verification through proportional scaling.
3Speed
If the LIN network operates at higher frequencies like 19.2 KHz, then the transmission speed increases, but the timing error magnitude increases causing more improper message rejections
Solution Approach 1:
The patent segments the budget verification into header and data portions, allowing the data budget to be calculated through direct proportional scaling (measured bit time × data byte count). This segmentation enables the system to handle higher transmission frequencies more accurately by applying the measured bit time as a precise scaling factor for the data portion, reducing the impact of timing errors at higher speeds.
Data Source
AI summary
Local Interconnect Network message budget calculation error is reduced by utilizing an eight bit time measurement of the sync byte in the message header. The method determines the header budget separately from the data budget, simplifying the required logic. The sync byte reference time is multiplied by the message data size to determine the data budget.