2.4. SEU Sensitivity Processing
In many instances, an SEU impacts CRAM bits that are not critical to the function of the design. For example:
- Configuration bits that are not used because they control unused logic and routing wires
- Portions such as test circuitry that are not utilized in the functional operations of the FPGA
- Non-critical functions that may be logged but do not need to be reprogrammed or reset
When planning recovery from an SEU, you must account for the time required to bring the FPGA to a state consistent with the current state of the system. For example, if an internal state machine is in an illegal state, it may require reset. In addition, the surrounding logic may need to account for this unexpected operation.
Typically, only 40% of all CRAM bits can be used even in the most heavily utilized device. This means that only 40% of SEUs require intervention and you can ignore the rest.