AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 9

• Manufacturer Part Number: AN2492
• Description: MPC184 Descriptor Programmers Guide--PCI View
• Manufacturer: Freescale Semiconductor / Motorola

Table 5 describes the AFEU mode register signals.
4.4 MDEU Mode Register
The MDEU mode register, shown in Figure 8, contains 8 bits which are used to program the MDEU. It also
reflects the value of burst size, which is loaded by the crypto-channel during normal operation with the
MPC184 as an initiator. Burst size is not relevant to target mode operations, where an external host pushes
and pulls data from the execution units.
The mode register is cleared when the MDEU is reset or re-initialized. Setting a reserved mode bit will
generate a data error. If the mode register is modified during processing, a context error will be generated.
MOTOROLA
31:11
10:8
Bits
7:3
2
1
0
Prevent permute
Context source
Dump context
Burst size
Signal
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MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
Reserved
The MPC184 implements flow control to allow larger than FIFO sized blocks of data to
be processed with a single key/context. The AFEU signals to the crypto-channel that a
‘burst size’ amount of data is available to be pushed to or pulled from the FIFO.
Note: The inclusion of this field in the AFEU mode register is to avoid confusing a user
who may read this register in debug mode. Burst size should not be written directly to
the AFEU.
Reserved
If set, this causes the context to be moved from the input FIFO into the S-box prior to
starting encryption/decryption. Otherwise, context should be directly written to the
context registers. Context source is only checked if the prevent permute bit is set.
0 Context not from FIFO
1 Context from input FIFO
If set, this causes the context to be moved from the S-box to the output FIFO following
assertion of AFEU’s done interrupt.
0 Do not dump context
1 After cipher, dump context
Normally, AFEU receives a key and uses that information to randomize the S-box. If
reusing a context from a previous descriptor or if in static assignment mode, this bit
should be set to prevent AFEU from reperforming this permutation step.
0 Perform S-box permutation
1 Do not permute
For More Information On This Product,
Table 5. AFEU Mode Register Signals
Go to: www.freescale.com
Description
Execution Unit Mode Data
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