AN3181

Class B solution structure

Doc ID 17286 Rev 2

27/31

4.4.6

Watchdog service in run mode test

If the run mode service block is correctly completed, then both window and independent

watchdogs (WDGs) are refreshed at the last step just before returning to the main loop. To

correctly refresh watchdogs, the user must ensure calling STL_DoRunTimeChecks()

routine (see Figure 12) at corresponding intervals in order to be able to properly react to the

time base flag change.

Only one WDG refresh inside the main loop is necessary and contributes to overall

efficiency. There should be no other WDG refresh except the one in

STL_DoRunTimeChecks() routine. Sometimes it is necessary to refresh WDGs at

initialization phase, too. In this instance, the refresh should be outside of any software

infinite loop.

4.4.7

Partial RAM run mode self test

Partial transparent RAM test is performed inside the time base interrupt service. The test

covers the part of the RAM containing the class B variables. One block of six bytes is tested

at every test step. To guarantee coupling fault coverage, consecutive test steps are

performed on memory blocks with an overlapping of two adjacent bytes. During the first

phase, the block content is stored in the storage buffer. The next phase is to perform the

marching destructive tests on all the bytes in the tested RAM block. Then, the final step is to

restore the original content. March X algorithm is faster as two middle marching steps are

skipped over (see Table 4). The last test sequence step is to perform a marching test on the

storage buffer itself, again with the next two additional bytes to cover coupling faults. Then

the whole test is re-initialized and it begins again. In case any fault is detected, FailSafe()

routine is called.

Figure 18.