51.4.9.1 Manual Mode

In Manual mode, the sequence is as follows:

  1. Set SHA_IER.DATRDY (Data Ready) , depending on whether an interrupt is required at the end of processing.
  2. If the initial hash values differ from the FIPS standard, set SHA_MR.UIHV and/or SHA_MR.UIEHV. If the initial hash values comply with the FIPS180 specification, clear SHA_MR.UIHV and/or SHA_MR.UIEHV.
  3. If automatic padding is required, configure SHA_MSR.MSGSIZE with the number of bytes of the message, and configure SHA_BCR.BYTCNT with the remaining number of bytes to write. The BYTCNT field must be written with a value different from MSGSIZE field value if the message is preprocessed and completed by using user initial hash values.
If automatic padding is not required, configure SHA_MSR.MSGSIZE and SHA_BCR.BYTCNT to 0.
  4. The FIRST command must be set by writing a 1 into the corresponding bit of the Control register (SHA_CR) to start a hash computation with initial constants (first block of a message) or to resume after message processing was interrupted. When a first message processing is interrupted to process another message, the intermediate hash results must be stored in the system memory and they must be reloaded in user initial values registers (IR0 accessed via SHA_IDATAR when SHA_CR.WUIHV=1) prior to resume and continue the processing of the first message. For the other blocks, there is nothing to write.
  5. Write the block to process in SHA_IDATARx.
  6. To begin processing, set SHA_CR.START.
  7. When processing is completed, the bit DATRDY in the Interrupt Status register (SHA_ISR) rises. If an interrupt has been enabled by setting SHA_IER.DATRDY, the interrupt line of the SHA is activated.
  8. Repeat the write procedure for each block (step 5), start procedure (step 6) and wait for the interrupt procedure (step 7) up to the last block of the entire message. Each time the start procedure is complete, the DATRDY flag is cleared.
  9. After the last block is processed (the DATRDY flag is set, if an interrupt was enabled by setting SHA_IER.DATRDY, the interrupt line of the SHA is activated), read the message digest in the Output Data registers. The DATRDY flag is automatically cleared when reading the SHA_IODATARx registers.