AMD Geode LX 800@0.9W - Manual (Page 520)

520 AMD Geode™ LX Processors Data Book
Security Block Register Descriptions 33234H
6.12.3 Security Block Configuration/Control Registers
6.12.3.1 SB Control A (SB_CTL_A)
2 SBI Swap Bits. This bit controls a bit-swapping feature within the AES module. When set,
the bits within each byte are swapped on both AES DMA reads and writes. Bit 7 is
swapped with bit 0, bit 6 is swapped with 1, etc. Asserting this bit does not affect the
slave operations to AES registers, (including the writable key), nor does it affect
EEPROM operations. When this bit is cleared, the DMA operations read and write bytes
with the same bit order as they appear in memory.
1:0 DIV AES Enable Divider. These two bits control the ratio between the GLIU clock frequency
and the updating of the AES encryption engine registers. The AES module is clocked at
the GLIU frequency, however, the state registers only update on an enable pulse that
occurs each n cycles, where n is determined by the DIV value. This register should not
be changed during an AES operation.
00: Divide by 1 (use for 100 MHz GLIU or less).
01: Divide by 2 (use for 100 MHz to 200 MHz GLIU).
10: Divide by 3 (use for 200 MHz to 300 MHz GLIU).
11: Divide by 4 (use for 300 MHz to 400 MHz GLIU).
SB Memory Offset 000h
Type
R/W
Reset Value 00000000h
GLD_MSR_CTRL Bit Descriptions (Continued)
Bit Name Description
SB_CTL_A Register Map
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
RSVD RSVD
CBC
A
SCA DCA WK
A
ECA ST
A
SB_CTL_A Register Bit Descriptions
Bit Name Description
31:8 RSVD Reserved.
7:6 RSVD Reserved. These bits are implemented but reserved for future use. When writing to this
register, software should set these bits to 0 and ignore them on read.
5 CBCA Cipher Block Chaining (CBC) Mode for A Pointer. When set, the AES engine
encrypts/decrypts using the Cipher Block Chaining Mode for the A pointer. When reset,
the AES engine encrypts/decrypts using the Electronic Codebook (ECB) Mode. No ini-
tialization vector is used when in ECB mode.
4 SCA Source Coherency for A Pointer Set. When set, the source memory fetches using the
GLIU interface are flagged as coherent operations. When reset, the operations are non-
coherent.
3 DCA Destination Coherency for A Pointer Set. When set, the destination memory writes
using the GLIU interface are flagged as coherent operations. When reset, the opera-
tions are non-coherent.
2 WKA Writable Key for A Pointer Set. When set, the AES engine uses the key from the writ-
able key register (SB Memory Offset 030h-03Ch) for its next operation. When reset, it
uses the hidden key value.
1 ECA Encrypt for A Pointer. When set, the AES operates in encryption mode. When reset, it
operates in decryption mode.