RM0444 Rev 5 513/1390
RM0444 AES hardware accelerator (AES)
522
20.7.2 AES status register (AES_SR)
Address offset: 0x04
Reset value: 0x0000 0000
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: Mode 4: key derivation then single decryption
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. Any attempt to selecting Mode 4 while either
ECB or CBC chaining mode is not selected, defaults to effective selection of Mode 3. It is not
possible to select a Mode 3 following a Mode 4.
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 Section 20.4.13: AES data registers and data swapping.
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.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. BUSY WRERR RDERR CCF
rrrr
Bits 31:4 Reserved, must be kept at reset value.
Bit 3 BUSY: Busy
This flag indicates whether AES is idle or busy during GCM payload encryption phase:
0: Idle
1: Busy
When the flag indicates “idle”, the current GCM encryption processing may be suspended to
process a higher-priority message. In other chaining modes, or in GCM phases other than payload
encryption, the flag must be ignored for the suspend process.
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