AN4266 datasheet(35/76 Pages) STMICROELECTRONICS

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AN4266

Functional safety requirements for application software

Doc ID 024283 Rev 2

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3.14.1

Synchronize Sequential Read Input

The CTU can be used if the customer needs to synchronize the reading of some inputs with

some events (FlexPWMs, eTimers, and/or external pins).

Mandatory: If this function is part of the application safety function, the safety integrity is

achieved by a mix of hardware mechanisms and software safety integrity functions

implemented at the application level:

●

CTU_HWSWTEST_TRIGGERNUM

●

CTU_SWTEST_TRIGGERTIME

●

CTU_HWSWTEST_TRIGGEROVERRUN

●

CTU_HWSWTEST_ADCCOMMAND (only if the input is an analog signal)

●

CTU_SWTEST_ETIMERCOMMAND

●

CTU_HW_CFGINTEGRITY

Note:

These functions are mandatory only if the CTU is used.

Software test implementation

●

CTU_HWSWTEST_TRIGGERNUM

If the reload signal occurs before all the triggers are generated, an overrun indication is

flagged and the application software must handle the error indication.

Note:

Rationale: Tests if all the triggers configured within a control period have been generated

and serviced.

Note:

Implementation hint: The Cross Triggering Unit Error Flag register (CTUEFR) shows

information about the overrun status.

●

CTU_SWTEST_TRIGGERTIME

Application software must configure one eTimer channel to capture the time at which

each trigger event occurs.

In triggered mode, the time instant of each trigger within one control period is captured

and stored in a FIFO. Application software has to check the FIFO values against the

expected ones according to CTU configuration.

In sequential mode, one eTimer channel is needed to check the correct time of a single

trigger with respect to the corresponding event.

Note:

Rationale: To verify if triggers are generated at the correct time

Note:

Implementation hint: Some eTimer inputs are internally connected to the CTU output.

eTIMER_2 input/outputs are not connected to pins on LQFP144 package. Use eTIMER_2

channels for implementing this safety function to keep the channels from eTIMER_0 or

eTIMER_1 units for functions using port pins (See “Enhanced Motor Control Timer (eTimer)”

in the SPC56xL70xx Reference Manual for details).

Note:

Implementation hint: eTimer capture register implements a two entry FIFO, but in CTU

triggered mode up to 8 time values need to be stored. To avoid FIFO overflow condition,

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