AN3077 datasheet(39/82 Pages) STMICROELECTRONICS

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AN3077

Functional safety requirements for application software

In CTU mode, the CTU module takes care of the hardware self-test activation, flow

monitoring, and timing. It is important to note that in this operating mode, the CPU does not

take part in running the hardware self-test.

HW self-tests use analog watchdogs to verify the outcome of self-test conversions. The

reference thresholds of these watchdogs are saved in test sector (See “Test flash memory”

section and “Test flash information” table in the Device_Number Reference Manual).

Mandatory: Before running the HW self-test, the customer must copy these thresholds from

the test sector into the watchdog registers (See “Self test analog watchdog” section of the

Device_Number Reference Manual).

Note:

Rationale: To set the correct threshold for the self-tests

Note:

Implementation hint: Since user can not directly read the test sector an SSCM feature,

called Test Flash Enable, shall be exploited. This action is performed through the following

steps:

If code is executing in flash memory, it jumps to execute from RAM.

Write SSCM_SCTR[TFE] = 1.

Test sector is readable at the offset 0x0 of the flash memory address space (See

“System Status and Configuration Module (SSCM)” of the Reference Manual).

Thresholds are copied from the test sector to the respective register.

Write SSCM_SCTR[TFE] = 0.

Code can continue execution from the flash memory.

BAM implements an access method to read the test sector.

Mandatory: Since the BAM is not developed according to the safety standard, a safety

application is not allowed to read the test sector through the BAM access method.

Additionally, a watchdog timer is implemented to check the sequence of the self-test

algorithms.

Mandatory: The customer must enable the watchdog timer for CPU mode and CTU mode.

The programmable watchdog timeout is the FTTI(h).

Note:

Rationale: To check the sequence of the self-test algorithms

Every hardware BIST is activated via a dedicated command sent to the ADC. Refer to the

“Self-testing” section in the “ADC” chapter of the Device_Number Reference Manual to have

all detailed instructions for implementing one of these modes.

The supply self-test must be executed without interleaved user conversion.

3.15.1.1.4

Software tests

●

ADC_SWTEST_TEST1

This software BIST exploits the presampling feature of the ADC. Presampling allows to

precharge or discharge the ADC internal capacitor before it starts the sampling and

conversion phases of the analog input coming from pads. During presampling phase,

This action is not mandatory in case of Double Read Analog Inputs.

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