AN3077 Datasheet, PDF (20/82 Pages) STMicroelectronics – Safety application guide

Functional safety requirements for application software
AN3077
Note:
Implementation hint: The eDMA and CRC modules may be used to implement this Safety
Integrity Function (SIF) to avoid overloading the CPU.
● GPI_SWTEST_CMP
This software test is used to execute the comparison between the double reads
performed by the independent channels.
3.13.1.1.4 Implementation details
The only hardware element that can be used for the safety function is the general purpose
input/output (GPIO).
Note:
Implementation hint: Every I/O pad that is not dedicated to a single function can be
configured as GPIO (ADC pads are an exception to this rule, as they can only be configured
as inputs).
Caution: Redundant GPIO shall be selected in a non-contiguous way from the pin perspective to
minimize CCF (see Section 7, I/O pin/ball configuration for details).
Mandatory: The pads shall be configured via the appropriate pad configuration registers
(PCRn) in the SIUL module.
Note:
Rationale: To configure pads used by this safety function, and avoid CCF caused by
improper configuration of the pads.
Table 3. Software BIST and/or test
Software BIST or test
Frequency
SIUL_SWTEST_REGCRC
Once after programming
GPI_SWTEST_CMP
Once for every acquisition
3.13.2
Read PWM Input
For ASIL D applications, digital inputs used for safety purposes are always assumed to be
acquired redundantly as described in the following section.
Read PWM Input means any input read related to signal transitions (rise or fall). This may
also include the time that the signal was high, low or both.
3.13.2.1 Double Read PWM Inputs
3.13.2.1.1
Hardware elements
A Double Read PWM Input is implemented by two channels, one channel provided by
eTimer_0 and the other by eTimer_1. The SIUL module must be configured (via the
appropriate SIUL_PCRn) to provide configuration and input direction of the input pads. To
minimize CCFs, these input pads must not be physically adjacent (see Section 7, I/O
pin/ball configuration for details).
3.13.2.1.2
Safety Integrity Functions
Safety integrity is achieved by reading each input then comparing the values in the
processing function (See Figure 2).
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