Table 22.
RAM_SM_6
SM CODE
RAM_SM_6
Description
Read protection (RDP) and write protection (WRP)
Ownership
ST
Detailed implementation
SRAM2 can be protected against illegal reads or erase/write by using these protection
features. The combination of these techniques and the related different protection level allows
End user
to build an effective access protection policy.
Error reporting
Refer to functional documentation - in some cases a HardFault error is generated.
Fault detection time
Refer to functional documentation
Addressed fault model
Systematic
Dependency on
Device
configuration
SRAM2 size may vary depending on part number.
Initialization
Not required
Periodicity
Continuous
Test for the diagnostic
Not applicable
Multiple-fault protection
Not required
Recommendations and known limitations
Hardware random-failure detection capability for SRAM2 access policy is restricted to well-
selected marginal failure modes, mainly affecting program counter and SRAM2 interface
functions. The associated diagnostic coverage is therefore expected to be irrelevant in the
framework of STM32L4 and Series safety concept.
3.6.4
Embedded Flash memory
Table 23.
FLASH_SM_0
SM CODE
FLASH_SM_0
Description
Periodic software test for Flash memory
Ownership
End user
or ST
Detailed implementation
Permanent faults affecting the system Flash memory interface address decoder are
addressed through a dedicated software test that checks the memory cells contents versus
the expected value, using signature-based techniques. According to IEC 61508:2 Table A.5,
the effective diagnostic coverage of such techniques depends on the width of the signature
in relation to the block length of the information to be protected - therefore the signature
computation method is to be carefully selected. Note that the simple signature method
(IEC 61508:7 - A.4.2 Modified checksum) is inadequate as it only achieves a low value of
coverage.
The information block does not need to be addressed with this test as it is not used during
normal operation (no data nor program fetch).
Error reporting
Depends on implementation
Fault detection time
Depends on implementation
Addressed fault model
Permanent
Dependency on
Device
configuration
Flash memory size changes according to the part number.
Initialization
Memory signatures must be stored in Flash memory as well.
Periodicity
Periodic
Test for the diagnostic
Self-diagnostic capabilities can be embedded in the software, according to the test
implementation design strategy chosen.
Multiple-fault protection
CPU_SM_0: Periodic core self-test software
CPU_SM_1: Control flow monitoring in
Application software
Recommendations and known limitations
This test is expected to have a relevant time duration – test integration must therefore
consider the impact on
Application software
execution.
UM2305
Hardware and software diagnostics
UM2305
-
Rev 10
page 21/110