RM0440 Rev 4 1521/2126
RM0440 AES hardware accelerator (AES)
1538
34.4.13 AES data registers and data swapping
Data input and output
A 128-bit data block is entered into the AES peripheral with four successive 32-bit word
writes into the AES_DINR register (bitfield DIN[31:0]), the most significant word (bits
[127:96]) first, the least significant word (bits [31:0]) last.
A 128-bit data block is retrieved from the AES peripheral with four successive 32-bit word
reads from the AES_DOUTR register (bitfield DOUT[31:0]), the most significant word (bits
[127:96]) first, the least significant word (bits [31:0]) last.
The 32-bit data word for AES_DINR register or from AES_DOUTR register is organized in
big endian order, that is:
• the most significant byte of a word to write into AES_DINR must be put on the lowest
address out of the four adjacent memory locations keeping the word to write, or
• the most significant byte of a word read from AES_DOUTR goes to the lowest address
out of the four adjacent memory locations receiving the word
For using DMA for input data block write into AES, the four words of the input block must be
stored in the memory consecutively and in big-endian order, that is, the most significant
word on the lowest address. See Section 34.4.16: AES DMA interface.
Data swapping
The AES peripheral can be configured to perform a bit-, a byte-, a half-word-, or no
swapping on the input data word in the AES_DINR register, before loading it to the AES
processing core, and on the data output from the AES processing core, before sending it to
the AES_DOUTR register. The choice depends on the type of data. For example, a byte
swapping is used for an ASCII text stream.
The data swap type is selected through the DATATYPE[1:0] bitfield of the AES_CR register.
The selection applies both to the input and the output of the AES core.
For different data swap types, Figure 525 shows the construction of AES processing core
input buffer data P127..0, from the input data entered through the AES_DINR register, or the
construction of the output data available through the AES_DOUTR register, from the AES
processing core output buffer data P127..0.
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