AN4253 datasheet(12/44 Pages) STMICROELECTRONICS

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FCCU block

AN4253

12/44

DocID024255 Rev 2

There are three different error paths reported by FCCU when any fault occurs:

Caution:

Whenever microcontroller is in safe mode, all faults in the FCCU status registers must be

cleared before any attempt to leave the safe mode.

4.1

FCCU status check

The first part of FCCU handler checks the state of the FCCU module after the reset. There

are four possibilities:

The FCCU handler shall resolve all states except NORMAL with the read, analyze, save

and clear procedure. No accesses to FCCU registers other than reading the

FCCU.CTRL.OPS shall be done between the setting of the key and the actual clear of the

status flag.

4.1.1

Code sequence

Write command OPR=3 to FCCU_CTRL register

Wait for operation to finish (FCCU.CTRL.OPS = SUCCESS)

Read the FCCU_STATUS register

Decide if Status == 0x0 (NORMAL)

4.2

Read critical and non-critical faults in FCCU (FCCU.CF/NCF)

The FCCU module contains two groups of faults, critical faults and non-critical faults. Both

groups should be read for later analysis.

•

Reset

Critical fault or non-critical fault with a configured reset reaction

•

Safe mode

FCCU fault state entry always initiates safe mode request, where

the HW resources are limited and the user has to solve the faults

before asking for a change of the mode.

•

NMI

FCCU fault state entry always generates non-maskable signal.

This signal will generate an exception to the core for faults without

reset generation reaction or in case when the reset is not present

because of a fault in the reset module (safety measure against

failures in RGM module)

•

NORMAL

Everything is fine from the point of FCCU module, a reset was

either destructive or caused by a non-critical fault that is masked in

the configuration, i.e. default behavior of SW functional reset.

•

ALARM

There is a non-critical fault pending in alarm state waiting for SW

intervention.

•

FAULT

All critical faults and non-critical faults without alarm timeout

enabled.

•

OTHER

Unknown state. It should not happen at all.

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