AN3077 Datasheet, PDF (22/82 Pages) STMicroelectronics – Safety application guide

Functional safety requirements for application software
AN3077
Note:
Implementation hint: The eDMA and CRC modules should be used to implement these
SIFs to avoid overloading the CPU.
● ETIMERI_SWTEST_CMP
This software BIST is used to execute the comparison between the double reads
performed by a channel on eTimer_0 and another channel on eTimer_1. The
comparison must take into account possible approximation because of different
capturing of the input asynchronous signals.
3.13.2.1.4
Note:
Note:
Implementation details
The following hardware elements shall be used for the safety function:
● eTimer_0 channels
● eTimer_1 channels
Mandatory: The user must select one channel from the eTimer_0 module and another from
the eTimer_1.
Rationale: To avoid CCF (eTimer_0 and eTimer_1 belonging to different lakes)
Mandatory: The pads shall be configured via the appropriate pad configuration registers
(SIUL_PCRn).
Rationale: To configure pads used by this safety function
Table 4. Software BIST and/or test
Software BIST or test
Frequency
ETIMER0_SWTEST_REGCRC
Once after programming
ETIMER1_SWTEST_REGCRC
Once after programming
SIUL_SWTEST_REGCRC
Once after programming
ETIMERI_SWTEST_CMP
Once for every acquisition
3.13.3
Read Encoder Inputs
For ASIL D applications, encoder inputs used for safety purposes are assumed to be
acquired redundantly as described in the following section.
Read Encoder Input means any input read related to signal transitions (rise or fall). This
may also include signals coming from an encoder.
3.13.3.1 Double Read Encoder Inputs
3.13.3.1.1
Hardware elements
A Double Read Encoder Input is implemented using two channels that can be provided by:
● eTimer_0
● eTimer_1
● SIUL
When both channels are provided by the timer units, the signals of one encoder must be
addressed to eTimer_0 and the signals of the other encoder must be addressed to
eTimer_1. Alternatively, one or both channels can be provided by the SIUL, which supports
interrupt based reading of encoder signals. This means the SIUL must use general purpose
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