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sbc4500 watchdog refresh doesnt work properly

Question asked by Thorben Kamp on Jun 3, 2019

Hey,

I need some help with  the sbc4500 watchdog refresh.

The window size is 128ms and all 100ms i am sending a seed to refresh. From this refresh i calculate the response and send it back to sbc. After a successfull refresh, the sbc generates a new LFSR. So far so good.

 

Now i having the problem, that the sbc doesnt accept the answer for some LFSR-Values:

For example:  the answer for 0xB2 is 0x4D. This works.

The answer for 0x64 is 0x9B. According to the calculator in the guidlines this is the correct. However, afterwards the LFSR won't generate a new Value. The Answer register shows a bad timing-error and error counter increases. After few more seeds, the µC restarts.

 

If i re-write the LFSR register before every seed with the default value 0xB2, the bad timing won't appear and µC won't restart. I tried also changing LRFS values in every seed. In some cases everything is fine in some the error counter increases.

However, to rewrite the register for every refresh can't be a long term solution. Do you have any ideas what i can try to fix it?

 

best regards,

Thorben

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