Dynamic Arithmetic Inspection for MCU Verification Accuracy
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Solution Overview
Problem
Existing CPU inspection methods, such as those described in Japanese unexamined patent publication No. 2007-293524, fail to accurately determine the arithmetic operation function of a CPU as they rely on pre-defined and fixed arithmetic problems and results, allowing CPUs to send pre-calculated answers without actual computation, leading to false determinations of normal operation.
Innovation Solution
An inspection system where the device to be inspected acquires constants from an inspection device and performs arithmetic operations on sequentially selected problems, sending the results back to the inspection device, which determines the CPU's arithmetic operation function by comparing the received results with its own calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fixed arithmetic problems and pre-calculated answers are used for CPU inspection, then the inspection process is simple and fast, but the inspection accuracy deteriorates because the CPU can send pre-calculated answers without actual computation
Solution Approach 1:
The patent applies dynamics by making the arithmetic problems dynamic rather than fixed. The inspection device generates different arithmetic problems with varying constants during the inspection process, preventing the CPU under inspection from using pre-calculated answers. This ensures that the CPU must perform actual arithmetic operations, thereby maintaining both inspection speed and accuracy.
Solution Approach 2:
The patent changes the parameters of the arithmetic problems by varying the constants used in calculations. Instead of using fixed arithmetic problems, the inspection device modifies the constants (e.g., changing numbers in addition, subtraction, multiplication, or division problems) to generate new problems dynamically. This parameter variation ensures that the CPU must perform real computations rather than retrieving pre-calculated results.
2Productivity
If the CPU stores answer contents in registers beforehand, then the inspection process is efficient, but the inspection reliability deteriorates because the CPU can send stored answers without actual calculation
Solution Approach 1:
The patent applies preliminary action by having the inspection device prepare and send the arithmetic problem and constant to the CPU under inspection before the calculation is performed. This ensures that the CPU must execute the arithmetic operation in real-time rather than retrieving pre-stored answers, thereby maintaining inspection efficiency while improving reliability.
Solution Approach 2:
The patent uses feedback by having the CPU under inspection send the result of its arithmetic operation back to the inspection device, which then compares the result with the expected correct answer. This feedback mechanism verifies that the CPU actually performed the calculation rather than sending pre-stored values, ensuring both efficiency and reliability in the inspection process.
3Device complexity
If a watch dog timer only checks for pulse signals at constant timing, then the timer function inspection is simple, but the arithmetic operation function inspection is insufficient
Solution Approach 1:
The patent applies universality by designing the inspection device to perform multiple functions: it generates arithmetic problems, sends constants to the CPU, receives calculation results, verifies correctness, and determines whether the arithmetic operation function is normal. This multi-functional approach allows a single inspection mechanism to comprehensively verify both timer and arithmetic operation functions without significantly increasing complexity.
Solution Approach 2:
The patent uses an intermediary approach by introducing arithmetic problems and constants as intermediate elements between the inspection device and the CPU. Instead of directly observing CPU operations, the inspection device uses arithmetic problems as intermediaries to indirectly verify the arithmetic operation function, maintaining simplicity while improving verification capability.
Data Source
AI summary
It is determined whether an arithmetic operation function of a device to be inspected is normal or not. A MCU 13 to be inspected acquires a constant to be used for an arithmetic problem from a power source IC 12 on an inspection side. The MCU 13 sequentially selects a plurality of the arithmetic problems and carries out an arithmetic operation using the acquired constant according to the selected arithmetic problem. A monitoring circuit 23 of the power source IC 12 receives the result of the arithmetic operation of the arithmetic problem from the MCU 13. The monitoring circuit 23 compares the received arithmetic operation result with the arithmetic operation result of the arithmetic problem calculated at the side of the monitoring circuit 23. The monitoring circuit 23 determines whether the arithmetic operation function of the MCU 13 works normally or not based on the comparison result.