AnsweredAssumed Answered

why i.MX258 can't keep programmed-key

Question asked by jingdar du on Dec 30, 2013
Latest reply on Jan 18, 2014 by YS Lin

Dear Sir,

We use i.MX258 as our production platform, after our device power-off, the programmed-key in dryice lost at all.

We have a coin-cell to save SCC when device power-off.

Please help out and answer below questions.

1,  Dryice has the same function with Engineering or Production mode, correct?

2,  Production / Engineering modes are related to SCC mostly, correct?

3,  Currently, SCC is not our current focus, so Production/Engineering modes should not play any key role, correct?

4,  Why  DryIce failed to keep keys in its volatile memory  AT ALL?

5, We are not sure it is the same issue which did report in ENGcm11122 (DryIce: Unexpected Reset) of Chip Errata for
the i.MX25). But based on the document, it should be fixed in silicon revision 1.2, and we did check our on hand chip and the revision is the latest one.

The DryIce module contains an internal power switch, which is used to switch between the backup battery input (BAT_VDD) and the system power (QVDD). When the system is powered off (shut down), the backup battery power is used by the DryIce module to maintain the RTC and the security features. The advantage of the battery backup power is, when the system is powered on
again, the SRTC features (time counter, monotonic counter, general purpose register, secure keys, and so on) are still valid. There is an error in the switching mechanism that may cause a reset in the DryIce module during the switch from the backup battery to system power. In turn, this invalidates the SRTC features when the system is powered on again. (same as ENGcm11122 which showed in Chip Errata for the i.MX25)