Compute Module • Re: RTC Backup domain memory with battery (CM5)

Given that the whole board has to go through the boot cycle on an RTC wake (including SDRAM init and OS load) before you get to do anything, why not use the filesystem for persistence?

Just my 2 cents.

I use an external battery backed RTC with 38 bytes user ram with the CM3.

I then use random data written in the RTC ram to encrypt a second partition in the CM3 eMMC for application security.

I have placed the RTC under the CM3 module to prevent physical access to the RTC chip and use naughty methods to remove power from the RTC if the CM3 module is removed. And the CM3 can't be placed in USB Boot mode while on my base board.

For this application I don't want to store the data in the flash where any attacker can read it out, and it would have been perfect if the CM5 had battery backed ram, as removing the module would automatically have removed power from the RTC(and erased the keys).

I do understand that this is a very niche application, but it is still an application...

Statistics: Posted by errolt — Thu Apr 10, 2025 1:45 pm

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