Table 141. Processing Latency For Gcm And Ccm (In Clock Cycles) - ST STM32WL55JC Reference Manual

AES hardware accelerator (AES)
Bit 8 ERRC: Error flag clear
Upon written to 1, this bit clears the RDERR and WRERR error flags in the AES_SR register:
0: No effect
1: Clear RDERR and WRERR flags
Reading the flag always returns zero.
Bit 7 CCFC: Computation complete flag clear
Upon written to 1, this bit clears the computation complete flag (CCF) in the AES_SR register:
0: No effect
1: Clear CCF
Reading the flag always returns zero.
Bits 16, 6:5 CHMOD[2:0]: Chaining mode selection
This bitfield selects the AES chaining mode:
000: Electronic codebook (ECB)
001: Cipher-block chaining (CBC)
010: Counter mode (CTR)
011: Galois counter mode (GCM) and Galois message authentication code (GMAC)
100: Counter with CBC-MAC (CCM)
others: Reserved
Attempts to write the bitfield are ignored when the EN bit of the AES_CR register is set before the
write access and it is not cleared by that write access.
Bits 4:3 MODE[1:0]: AES operating mode
This bitfield selects the AES operating mode:
00: Mode 1: encryption
01: Mode 2: key derivation (or key preparation for ECB/CBC decryption)
10: Mode 3: decryption
11: Reserved
Attempts to write the bitfield are ignored when the EN bit of the AES_CR register is set before the
write access and it is not cleared by that write access.
Bits 2:1 DATATYPE[1:0]: Data type selection
This bitfield defines the format of data written in the AES_DINR register or read from the
AES_DOUTR register, through selecting the mode of data swapping:
00: None
01: Half-word (16-bit)
10: Byte (8-bit)
11: Bit
For more details, refer to
Attempts to write the bitfield are ignored when the EN bit of the AES_CR register is set before the
write access and it is not cleared by that write access.
Bit 0 EN: AES enable
This bit enables/disables the AES peripheral:
0: Disable
1: Enable
At any moment, clearing then setting the bit re-initializes the AES peripheral.
This bit is automatically cleared by hardware upon the completion of the key preparation (Mode 2)
and upon the completion of GCM/GMAC/CCM initial phase.
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Section 23.4.13: AES data registers and data
RM0453 Rev 2
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swapping.