ST STM32F2 Series User Manual page 28

SM CODE
Detailed implementation
Error reporting
Fault detection time
Addressed fault model
Dependency on MCU
configuration
Initialization
Periodicity
Test for the diagnostic
Multiple faults protection
Recommendations and known
limitations
UM1845 - Rev 4
NVIC_SM_1
According to IEC 61508:2 Table A.1 recommendations, a diagnostic measure for continuous, absence or
cross-over of interrupt must be implemented. The method of expected and unexpected interrupt check is
implemented at application software level.
The guidelines for the implementation of the method are the following:
• The list of the implemented interrupt for the MCU are well documented, reporting also the expected
frequency of each request when possible (for example the interrupts related to ADC conversion
completion, therefore coming on a deterministic way).
• Individual counters are maintained for each interrupt request served, in order to detect in a given time
frame the cases of a) no interrupt at all b) too many interrupt requests ("babbling idiot" interrupt
source). The control of the time frame duration must be regulated according to the individual interrupt
expected frequency.
• Interrupt vectors related to unused interrupt source point to a default handler that reports, in case of
triggering, a faulty condition (unexpected interrupt).
• In case an interrupt service routine is shared between different sources, a plausibility check on the
caller identity is implemented.
• Interrupt requests related to non-safety-related peripherals are handled with the same method here
described, despite their originator safety classification
Depends on implementation
Depends on implementation
Permanent and Transient
None
Depends on implementation
Continuous
Not needed
CPU_SM_0: periodical core self-test software
In order to decrease the complexity of method implementation, it is suggested to use polling technique
(when possible) instead of interrupt for end system implementation
Description of hardware and software diagnostics
UM1845
page 28/108