SM CODE SPI_SM_2
Detailed implementation
This method is implemented adding to data packets transferred by SPI a redundancy check
(such as a CRC check, or similar one) with encoding capability. The checksum encoding
capability must be robust enough to guarantee at least 90% probability of detection for a
single bit flip in the data packet.
Consistency of data packet must be checked by Application software before consuming data.
Error reporting Depends on implementation
Fault detection time Depends on implementation
Addressed fault model Permanent/transient
Dependency on Device configuration None
Initialization Depends on implementation
Periodicity On demand
Test for the diagnostic Not applicable
Multiple-fault protection CPU_SM_0: Periodic core self-test software
Recommendations and known limitations
It is assumed that the remote SPI counterpart has an equivalent capability of performing the
check described.
To give an example on checksum encoding capability, using just a bit-by-bit addition is
unappropriated.
Table 130. SPI_SM_3
SM CODE SPI_SM_3
Description CRC packet-level
Ownership ST
Detailed implementation
SPI communication module allows to activate automatic insertion (and check) of CRC-8 or
CRC-18 checksums to packet data.
Error reporting Error flag raise and optional Interrupt Event generation
Fault detection time
Depends on peripheral configuration (for example baud rate). Refer to functional
documentation.
Addressed fault model Permanent/transient
Dependency on Device configuration None
Initialization Depends on implementation
Periodicity Continuous
Test for the diagnostic
Direct test procedure for CRC efficiency is not available. CRC run-time hardware failures
leading to disabling such protection fall into multiple-fault scenario, from IEC61508
perspective. Related failures are adequately mitigated by the combination of safety
mechanisms reported in this table, field Multiple-fault protection.
Multiple-fault protection SPI_SM_2: Information redundancy techniques on messages
Recommendations and known limitations
This method can be part of the implementation for SPI_SM_2 or SPI_SM_4. In that case,
because of the warning issued in the Test for the diagnostic field, this mechanism can not be
the only one to guarantee message integrity.
Table 131. SPI_SM_4
SM CODE SPI_SM_4
Description Information redundancy techniques on messages, including end-to-end protection
Ownership End user
UM2305
Hardware and software diagnostics
UM2305 - Rev 10
page 73/110
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