Si102x/3x
14.4.1. AES Block Cipher Encryption using DMA
Normally, the AES block is used with the DMA. This provides the best performance and lowest power con-
sumption. Code examples are provided in 8051 compiler independent C code using the DMA. It is highly
recommended to use the code examples. The steps are listed here for completeness.
Steps to encrypt data using Simple AES block encryption (ECB mode)
Prepare encryption Key and data to be encrypted in xram.
Reset AES module by clearing bit 2 of AES0BCFG.
Disable the first three DMA channels by clearing bits 0 to 2 in DMA0EN.
Configure the first DMA channel for AES0KIN
the first DMA channel by writing 0x00 to DMA0SEL
Configure the second DMA channel to move XRAM to AES0KIN by writing 0x05 to DMA0NCF
Write 0x01 to DMA0NMD to enable wrapping
Write the XRAM location of the encryption key to DMA0NBAH and DMA0NBAL.
Write the key length in bytes to DMA0NSZL
Clear DMA0NSZH
Clear DMA0NAOH and DMA0NAOL.
Select
Configure the second DMA channel for AES0BIN sfr.
the second DMA channel by writing 0x01 to DMA0SEL.
Configure the second DMA channel to move XRAM to AES0BIN by writing 0x06 to DMA0NCF.
Clear DMA0NMD to disable wrapping.
Write the XRAM address of the data to be encrypted to DMA0NBAH and DMA0NBAL.
Write the number of bytes to be encrypted in multiples of 16 bytes to DMA0NSZH and DMA0NSZL.
Clear DMA0NAOH and DMA0NAOL.
Select
Configure the third DMA channel for AES0YOUT
Select
the third DMA channel by writing 0x02 to DMA0SEL
Configure the third DMA channel to move the contents of AES0YOU to XRAM by writing 0x08 to DMA0NCF.
Enable transfer complete interrupt by setting bit 7 of DMA0NCF.
Clear DMA0NMD to disable wrapping.
Write the XRAM address for the encrypted data to DMA0NBAH and DMA0NBAL.
Write the number of bytes to be encrypted in multiples of 16 bytes to DMA0NSZH and DMA0NSZL.
Clear DMA0NAOH and DMA0NAOL.
Clear first three DMA interrupts by clearing bits 0 to 2 in DMA0INT.
Enable first three DMA channels by setting bits 0 to 2 in DMA0EN.
Configure the AES module data flow for AES Block Cipher by writing 0x00 to AES0DCFG.
Write key size to bits 1 and 0 of AES0BCFG
Configure the AES core for encryption by setting bit 2 of AES0BCFG
Initiate the encryption operation be setting bit 3 of AES0BCFG
Wait on the DMA interrupt from DMA channel 2
Disable the AES module by clearing bit 2 of AES0BCFG
Disable the DMA by writing 0x00 to DMA0EN
Rev. 0.3
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