AN4253 datasheet(10/44 Pages) STMICROELECTRONICS

10 / 44 page

SSCM HW configuration check

AN4253

10/44

DocID024255 Rev 2

SSCM HW configuration check

Figure 4. Flow of the "SSCM HW configuration check" phase

Before the microcontroller exits the Reset phase several operations are executed. One of

them is device HW configuration controlled by System Status and Configuration module

(SSCM). Target of the configuration process is to setup all important analog modules to

predefined factory setting plus to initialize default values of several key registers.

Configuration values are stored in the shadow flash memory region which is read by SSCM

module during reset phase. As any other flash memory it can happen that values stored

there are corrupted with multi bit error. Unlike the application exception system triggering

ECC fault in such case, the SSCM module does not have such possibility. The system is still

under reset. The SSCM module behavior is that it ignores any ECC faults that might happen

during read operation.

The consequence of such silent behavior is that the device can be configured wrongly. Such

faulty configuration can remain unnoticed or can have severe safety impact in the

application. The distinction between the two is difficult because there is no trace information

which data were corrupted and how much.

There is only one possible check to identify if an ECC fault occurred or not. Any read

operation from flash memory having ECC fault leaves MCR.EER bit inside the flash module

registers set regardless if the read operation is executed by the Core or SSCM module. This

can be used to identify if the SSCM module has faced ECC error during configuration or not.

3.1

Code sequence

Read FLASH.MCR register (0xC3F8_8000)

Test EER bit (bit 16)

If set (‘1’) => ECC fault has happened, might be wrong device

configuration => SSCM Faul Handler

3.2

SSCM fault handler

SSCM fault handler is an application specific piece of code. Most probable solution would

be to trigger a long reset or external one to re-run SSCM configuration.

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