8.9.5.4 Enhanced Conditioning by Hamming Distance Checking

Conditioning a new random sample with only a difference may not be enough for the application, thus it is possible to perform a check on the Hamming distance between two consecutive random samples before asserting the TRNG_ISR.DATRDY flag.

When TRNG_MR.HD=1, any new internal data sample (every 84 or 168 MCK clock cycles) is first checked against the previous data and the TRNG_ISR.DATRDY flag is set if the Hamming distance is greater or equal to the value configured in the field TRNG_MR.HDSEL. When TRNG_MR.HD=1, the maximum streaming rate can be slightly slower compared to TRNG_MR.HD=0.

The Hamming distance can be configured to be greater than or equal to 2,4,8 or 16.

To prevent excessive waiting time before getting the next data sample with the expected Hamming distance, a timeout is implemented after sixteen internal data sample periods for which the data did not match the required condition. If the timeout occurs, the previous data is automatically negated (binary format).