7.2.4.9 Automatic Padding Mode
When Automatic Padding mode is configured, the message is automatically padded after the last block is written. Depending on the size of the message, either a padding is performed after the last part of the message and padding blocks are added, or only padding blocks are added.
IPSec and SSL padding standards are both supported.
The auto padding feature only supports CBC and CTR modes.
Note: When automatic padding is enabled and AES_MR.SMOD=2, AES_MR.DUALBUFF must be
cleared.