AN3307 datasheet(33/37 Pages) STMICROELECTRONICS

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AN3307

Class B solution structure

Doc ID 18186 Rev 4

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5.4.5

Partial Flash CRC runtime self-test

The partial 16-bit CRC checksum of the block in Flash is performed at each step. The

boundaries are given by the structure stored by the linker. When the last block is reached,

the CRC checksum is compared with the value stored by the linker. If a difference is found,

the Fail Safe routine is called, otherwise a new computation cycle is initialized. Refer also to

Section 4.3.3: Debugging the package for additional comments on CRC procedures.

Figure 19.

Partial Flash CRC runtime self-test structure

5.4.6

Watchdog service in runtime test

If the runtime service block is successfully completed, the window and independent

watchdogs should both be refreshed as a last step, just before returning to the main loop.

For the watchdogs to be refreshed correctly, proper timing of the call to the runtime block is

essential. The period when the block should be called is signaled internally by a time base

flag which is tested at the beginning of the STL_DoRunTimeChecks() routine (see

Figure 15). Users must ensure not to miss calling this procedure at the main level to be able

to react properly to any change in the time base flag and consequently refresh the

watchdogs at the correct intervals.

To use the watchdogs efficiently, it is important to keep the structure of the application with

only one refresh placed in the main loop. There should be no other watchdog refreshes

except the one in the STL_DoRunTimeChecks() routine. Sometimes it may also be

necessary to refresh watchdogs in the initialization phase of the flow. In this case, the

refresh should be outside any software infinite loop. Ideally it should only be put in a

straightforward part of the code.

Compute continuous CRC

FLASH_pointer

at ROM_END?

CRC =

_checksum?

FLASH_Pointer ++

Test On going

Init CRC computation

Test OK

FailSafe () routine

Yes

AI18016

AN3307 Datasheet(PDF) 33 Page - STMicroelectronics