SM CODE
UART_SM_2
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 USART1/2/3/4/5/6/7/8 and LPUART 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 126.
UART_SM_3
SM CODE
UART_SM_3
Description
Information redundancy techniques on messages, including end-to-end protection
Ownership
End user
Detailed implementation
This method aims to protect the communication between a peripheral and his external
counterpart establishing a kind of “protected” channel. The aim is to specifically address
communication failure modes as reported in IEC61508:2, 7.4.11.1.
Implementation guidelines are as follows:
•
Data packet must be protected (encapsulated) by an information redundancy check,
like for instance a CRC checksum computed over the packet and added to payload.
Checksum encoding capability must be robust enough to guarantee at least 90%
probability of detection for a single-bit flip in the data packet.
•
Additional field added in payload reporting an unique identification of sender or receiver
and an unique increasing sequence packet number.
•
Timing monitoring of the message exchange (for example check the message
arrival within the expected time window), detecting therefore missed message arrival
conditions.
•
Application software
must verify before consuming data packet its consistency (CRC
check), its legitimacy (sender or receiver) and the sequence correctness (sequence
number check, no packets lost).
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
A major overlap between the requirements of this method and the implementation of complex
communication software protocols can exists. Due to large adoption of these protocols in
industrial applications, optimizations can be possible.
It is assumed that the remote counterpart has an equivalent capability of performing the
checks described.
UM2305
Hardware and software diagnostics
UM2305
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Rev 10
page 71/110
