AN4266 datasheet(31/76 Pages) STMICROELECTRONICS

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AN4266

Functional safety requirements for application software

Doc ID 024283 Rev 2

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Mandatory: The output write of a redundant PWM channel must be implemented by writing

the new output values to both the PWM channels. The customer can decide whether to use

both eTimers (eTimer_0, eTimer_1) or both FlexPWMs (FlexPWM_0, FlexPWM_1), See

Figure 6.

Note:

Rationale: To write a digital output by exploiting redundancy, and modules must belong to

different lakes to decrease the probability of CCF

Implementation details

The following hardware elements shall be used for the safety function:

●

eTimer_0 channels

●

eTimer_1 channels

●

FlexPWM_0 channels

●

FlexPWM_1 channels

Mandatory: The pads shall be configured via the appropriate pad configuration registers

(PCRn) in the SIUL module.

Note:

Rationale: To configure pads used by this safety function

Single Write PWM Outputs With Read Back

The hardware elements eTimer_0 and FlexPWM_1 or eTimer_1 and FlexPWM_0 are used

to perform a Write PWM Output With Read Back(f). These units must be configured to

implement one PWM output channel and (via internal read back) the eTimer_0 input PWM

channel. The SIUL must be configured to define the configuration of the output pads used.

The software must perform a write operation followed by a read operation. To guarantee the

integrity of the two output channels, the application should test the SIUL configuration

implementing the SIUL_SWTEST_REGCRC (to avoid a common failure caused by

misconfiguration of the pads).

Table 8.

Software BIST and/or test

Software BIST or test

Frequency

SIUL_SWTEST_REGCRC

Once after programming(1)

If a change in a single SIUL configuration register is capable of affecting both the output and the read-back

paths, then SIUL_SWTEST_REGCRC must be executed every FTTI. In all other cases configuration

errors are covered by the software comparison.

ETIMER0_SWTEST_REGCRC(2)

This software BIST is needed only if the FlexPWM channels are used for the safety function

Once after programming

ETIMER1_SWTEST_REGCRC(2)

Once after programming

FLEXPWM0_SWTEST_REGCRC(3)

This software BIST is needed only if the eTimer channels are used for the safety function

Once after programming

FLEXPWM1_SWTEST_REGCRC(3)

Once after programming

PWMDW_SWAPP_WRITE

Once every write

eTimer_0 and FlexPWM_0 (eTimer_1 and FlexPWM_1) cannot be used in combination due to the same LBIST

partition assignment.

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