ECC + checksum have a slight flaw.
If too many errors happens, the checksum can be correct even though the content is corrupted.
Hum... I know what you think: ThisShouldNeverHappen
When exploited by human it is called a collision attack. Works pretty well, so many people trust but never check.
1. Store embedded system state in data structure.
2. Calculate a checksum for that data structure.
3. Verify that checksum is correct.
HW Solution:
Lockstep Execution/ECC memory, etc.