Fail-Safe Time Function Using Dual Interrupt Service Routines
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Solution Overview
Problem
Current timer monitoring systems are not secure enough to meet standards like IEC61508 and require additional hardware, which is not feasible for all systems, especially those needing high accuracy with minimal error tolerance.
Innovation Solution
Utilizing system crystals to generate time signals, with one crystal for the standard time and another for the monitoring time, allowing for a fail-safe time function without additional hardware components, by redirecting and processing interrupt signals through the Interrupt Service Routine and modifying the interrupt descriptor table to maintain system integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second timer (F-Timer) is installed to monitor the time base accuracy, then the time monitoring reliability is improved, but the device complexity increases due to required hardware extensions
Solution Approach 1:
The patent makes the existing interrupt system perform dual functions: it continues to handle standard interrupt requests while simultaneously enabling time base monitoring through the F-Timer. The interrupt controller and service routines are configured to serve both conventional timing operations and safety-critical time monitoring, eliminating the need for separate dedicated monitoring hardware
Solution Approach 2:
The system uses its own existing interrupt infrastructure and processing capabilities to perform self-monitoring of the time base. The F-Timer leverages the system's built-in interrupt controller, service routine mechanisms, and processor resources to autonomously verify time base accuracy without requiring external monitoring equipment
2Measurement precision
If the clock rate of the periodic interrupt signal is increased to improve monitoring accuracy, then the time measurement precision is improved, but the risk of interrupt loss during long interrupt blocks increases
Solution Approach 1:
The patent dynamically adjusts the interrupt frequency based on the specific monitoring requirements and system conditions. The F-Timer can operate at different clock rates (e.g., 8.192 kHz or 1.024 kHz) depending on the desired balance between measurement precision and interrupt reliability, allowing flexible adaptation to various operational scenarios
Solution Approach 2:
The system changes the parameter of interrupt frequency to optimize performance. By selecting appropriate clock rates for the F-Timer, the system can achieve sufficient time measurement precision while maintaining interrupt signal reliability, even in the presence of long interrupt blocks from the operating system
Data Source
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AI summary
The method involves generating a periodic interrupt signal via internal real time clock quartz (Q2), where the periodic interrupt signal possesses preset frequency and clock cycle. A table item in a system internal-interrupt descriptor table is accessed with reference to an interrupt service routine during receiving the periodic interrupt signal. A counter is formed via the routine. A clock rate of the interrupt signal is increased, and additional interrupt signals are filtered out. An independent claim is also included for a device for implementation of a fail-safe time function.