7.6.5.8.2 Failures
If a failure (e.g. PUF SRAM access error) is detected, either during Initialization, Zeroization or other operations, the PUF controller reports a failure result code in the PUF Operation Result Register (PUF_ORR.RCODE > 0xFA) and enters the Locked state. When the PUF controller is in Locked state, no operations other than Zeroize can be performed. The software must determine if a Zeroize operation is required.
The following table shows the possible failure result codes for each operation type.
| Operation / Result Code | Description | Possible Action |
|---|---|---|
| All Operations | ||
| All / FAILURE_SRAM | PUF SRAM access failed. | Try to repower the PUF or the product. |
| Initialization | ||
| Initialization / FAILURE_DRBG_HEALTH | One or more of the DRNG health tests failed (hardware is out of order, or has intermittent failure). | Try to repower the PUF or the product. |
| Initialization / FAILURE_SETTINGS | An illegal combination of values is read in PUF_HW_SETTINGS. | None |
| Initialization / FAILURE_DRBG1_ENTROPY | The entropy test for DRBG 1 failed. | Try to repower the PUF or the product. |
| Initialization / FAILURE_DRBG2_ENTROPY | Activation of DRBG 2 failed (DRBG 1 cannot provide entropy). | Try to repower the PUF or the product. |
| Reseed | ||
| Reseed / FAILURE_DRBG2_ENTROPY | Reseed of DRBG 2 failed (DRBG 1 cannot provide entropy). | Try to repower the PUF or the product. |