Interrupt Checker Circuit Using Timestamps for Fault Detection

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Solution Overview

Problem

Existing software-based safety mechanisms struggle to effectively monitor and manage the complex array of interrupt signals in automotive microcontrollers, particularly in ensuring compliance with ISO 26262 safety standards, due to the sheer volume of concurrent demands and potential for unpredictable malfunctions.

Innovation Solution

A hardware-based interrupt checker circuit that utilizes timestamp checker circuits to monitor the elapsed time between interrupt events, generating error signals if the time difference exceeds predefined thresholds, thereby ensuring compliance with ISO 26262 safety standards without significantly increasing the size or complexity of the microcontroller.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If software-based safety mechanisms are used to monitor interrupt signals, then compliance with ISO 26262 safety standards can be achieved, but the system becomes vulnerable to unpredictable malfunctions and cannot effectively handle the complex array of concurrent interrupt signals

Engineering Contradiction:

Improvesafety mechanism reliabilityVSAvoidsoftware complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces software-based safety monitoring mechanisms with a hardware-based interrupt checker circuit. This circuit uses dedicated hardware components including timestamp registers, comparison logic, and error flag mechanisms to monitor interrupt signals. The hardware implementation provides deterministic behavior and immunity to software malfunctions while maintaining compliance with ISO 26262 safety standards through systematic monitoring of interrupt timing characteristics.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If hardware-based interrupt monitoring is implemented to improve reliability, then the system can detect unexpected malfunctions effectively, but the physical size and hardware complexity of the microcontroller increases

Engineering Contradiction:

Improveinterrupt monitoring reliabilityVSAvoidmicrocontroller area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The interrupt checker circuit is integrated directly into the microcontroller's interrupt controller unit, merging the safety monitoring functionality with the existing interrupt handling infrastructure. This integration allows the hardware-based monitoring to be implemented using the microcontroller's existing resource fabric including clocks, buses, and logic elements, thereby minimizing the additional area required while providing comprehensive interrupt signal monitoring and error detection capabilities.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20260003710A1Interrupt integrity check

Publication Date: 2026.01.01 STMICROELECTRONICS INT NV

AI summary

According to an embodiment, an interrupt checker circuit includes a timestamp checker circuit having a first input terminal coupled to an interrupt signal. A second input terminal of the timestamp checker circuit is configured to receive a global time reference. The timestamp checker circuit is configured to record a first timestamp corresponding to a first interrupt event at the first input terminal of the timestamp checker circuit based on the global time reference, record a second timestamp corresponding to a second interrupt event at the first input terminal of the timestamp checker circuit based on the global time reference, and compare a time difference between the second timestamp and the first timestamp to an expected duration and, based thereon, generate an error signal in response to the time difference being outside the expected duration.