Digi NS9215 manual AES buffer descriptor diagram, Source address pointer, Source buffer length

AES buffer descriptor diagram

OFFSET + 0

OFFSET + 4

OFFSET + 8

OFFSET + C

A E S D A T A E N C R Y P T I O N / D E C R Y P T I O N M O D U L E	. .
AES DMA buffer descriptor..
	.

31	30	29	28			16	15		0
					Source address
		Destination buffer length						Source buffer length
					Destination address
W	I	L	F	Reserved	AES Op			AES control

Source address [pointer]

Field definitions follow.

The source address pointer identifies the starting location of the source data. The source address can be aligned to any byte boundary.

Note: Optimal performance is achieved when the source address is aligned on a word boundary.

Source buffer length

The source buffer length indicates the number of bytes to be read from the source. After completing the transfer, the DMA controller updates this field with the actual number of bytes that were moved. This is useful for debugging error conditions or determining the number of bytes transferred before the DONE signal was asserted.

Destination buffer length

The destination buffer length indicates the number of bytes to be written to the destination. This field should be identical to the source buffer length for all modes — with the exception of CCM — when the authentication code is being generated or a key is being expanded.

Destination address [pointer]

AES control

The description address pointer field identifies the starting location of the source data’s destination; that is, to where the source data needs to be moved. The destination address must be word-aligned.

Bits	Used for	Values
[2:0]	Encryption mode select	000	CBC
		001	CFB
		010	OFB
		011	CTR
		100	ECB
		101	CCM
		111	Key expand mode, which allows a key to be
			expanded by the hardware key expander and
			written back to system memory
[3]	Encryption/decryption select	0	Encryption
		1	Decryption

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