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Abstract

A watchdog-type fail-safe system monitors program execution by a computer used, e.g., in controlling operation of an automative vehicle engine. The system includes a control unit, with a microprocessor; and a memory, which stores program segments. These segments include a main routine for performing a background job (BGJ), and a plurality of interrupt routines for handling event generated interrupts. Completion of the BGJ causes transition of an emergency decision signal, provided by the control unit, to a first level. Initiation of a particular first interrupt routine causes transition of the decision signal to a second level. Abnormalities in program execution may result in non-transition of the decision signal. If there is non-transition of the decision signal for greater than a predetermined reference time period, a fault condition signal is generated. This may initiate various emergency procedures, e.g., stopping or resetting the computer, and visual or audio alarms. Detectable abnormalities include; non-return to the BGJ from any one of the interrupt routines; non-completion of the BGJ due to an excessive number of interrupts, as might occur due to unusally high engine speed; or non-advancement to processing of an interrupt, even though the control unit accepted a valid interrupt demand, as might occur due to temporary troubles in vibration susceptible signal lines between the computer and engine.

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First Claim