AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 21

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

multiple subsequent) descriptor contains length/pointer pairs to the data to be permuted. Because the key
and context are unchanging over multiple packets (or descriptors), the series of short reads and writes
required to setup and tear down a session are avoided. This savings, along with the crypto-channel having
dedicated execution units, can represent a noticeable performance improvement.
Note that there is no mechanism for resetting an EU automatically when statically assigned, or when
assignment is changed from static to dynamic. Therefore, it is recommended that the drivers always reset
an EU just prior to removing a static assignment to it to prevent the previously used context from polluting
another encryption stream.
For example, statically assigning a DEU to a particular crypto-channel permits the DEU to retain context
between data packets. The following descriptors, listed in Table 15 through Table 17, support context
retention. Table 15 defines the first DPD_3DES_CBC_Encrypt descriptor in the static chain.
Table 16 defines the second (or N middle) DPD_3DES_CBC_Encrypt descriptor in the static chain. Note
that the IV and key are not loaded, as they remain in the DEU key and IV register.
MOTOROLA
Header
LEN_1
PTR_1
LEN_2
PTR_2
LEN_3
PTR_3
LEN_4
PTR_4
LEN_5
PTR_5
LEN_6
PTR_6
LEN_7
PTR_7
PTR_NEXT
Header
LEN_1
PTR_1
Field
Field
Table 15. Actual Descriptor DPD_Type 0001_3DES_CBC_Encrypt
Table 16. Actual Descriptor DPD_Type 0001_3DES_CBC_Encrypt
MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
0x2070_0010
0x2070_0010
Value/Type
Value/Type
For More Information On This Product,
Pointer
Pointer
Pointer
Pointer
Pointer
Pointer
Length
Length
Length
Length
Length
Pointer
Length
Nul
Nul
Nul
Nul
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DPD_Type 0001_3DES_CBC_Encrypt
Null
Null
Number of bytes of IV to be written to DEU IV register (always 8)
PCI address of IV
Number of bytes of key to be written to DEU key register (must be
16 or 24)
PCI address of key
Number of bytes to be ciphered
PCI address of data to be ciphered
Bytes to be written (should be equal to length of data-in)
PCI address where ciphered data is to be written
Null
Null
Null
Null
Pointer to next descriptor
DPD_Type 0001_3DES_CBC_Encrypt
Null
Null
Description
Description
Descriptor Classes
21