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eFuse lock bits with random setting

Question asked by jschoen on Mar 27, 2014
Latest reply on Apr 8, 2014 by Lily Zhang

We are seeing an occasional issue where efuse address 0, OTP Bank0 Word0 (Lock controls), i.e., shadow register OCOTP_LOCK, does not contain the factory default value of 0x20220002.  Maybe 2 or 3 out of 100 processors will have other random bits set causing, for example the Ethernet MAC address to be locked and not writable.  We have seen 0x20220003, 0x20220012, 0x 20220202.


We are reading and writing the fuses through a version of u-boot that is loaded over USB during factory test.  Thinking that u-boot’s efuse write function may have a bug, we added code to read the lock fuse before doing any fuse writes and we are reading bit errors there too making us think the processors may be coming from Freescale with random lock bits set in error.


Has anyone else seen anything like this problem before?