AN4253 datasheet(14/44 Pages) STMICROELECTRONICS

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FCCU block

AN4253

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DocID024255 Rev 2

In such case it is necessary to store the read values somewhere else.

Some possibilities are:

•

Non-volatile RAM used to exchange data between the startup code and the application.

In case of destructive reset, code has to initialize non-volatile block to default values.

•

One of the core registers like SPRGx. These registers are usually used by the

application or operating system for non specific purposes.

4.6

Reset FCCU faults

Any fault latched by the FCCU prevents successful transition from Safe mode to DRUN.

Therefore whenever the microcontroller is in safe mode, FCCU flags must be cleared before

executing mode transition.

4.6.1

Code sequence

Clearing Critical Faults (CF) sequence

Write the Key 0x618B7A50 to FCCU_CFK register

Write CF status value back to FCCU_CF register

Wait for operation to finish (OPS == SUCCESS)

Clearing Non-Critical Faults (NCF) sequence

Write the Key 0xAB3498FE to FCCU_NCFK register

Write NCF status back to FCCU_NCF register

Wait for operation to finish (OPS == SUCCESS)

4.7

FCCU fault handler

FCCU fault handler is an application specific piece of code. There might be several

possibilities like:

•

Analyzing which LBIST partition or MBIST block failed and decide if it is critical for the

application or not.

Example can be failing memory block belonging to Flexray module. If Flexray module is

not used then the fault found by STCU self test is of no harm for the application and

startup can continue.

•

Generate destructive reset to restart microcontroller from the very beginning including

STCU Self tests. If the fault was because of a temporary failure, re-initiated self test will

finish ok, which enables to continue with the startup.

AN4253 датащи(PDF) 14 Page - STMicroelectronics