AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 20

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

Descriptor Classes
Descriptor Classes
7.1 Null Fields
On occasion, a descriptor field may not be applicable to the requested service. With seven length/pointer
pairs, it is possible that not all descriptor fields will be required to load the required keys, context, and data.
(Some operations don’t require context, others may only need to fetch a small, contiguous block of data.)
Therefore, when processing data packet descriptors, the MPC184 will skip any pointer entirely that has an
associated length of zero.
8 Descriptor Classes
The MPC184 has two general classes of descriptors: static, which refers to a relatively unchanging usage of
MPC184 resources, and dynamic, which refers to a continually changing usage model.
8.1
Recall that the MPC184 has six execution units and four crypto-channels. The EUs can be statically
assigned, dedicating them to a particular crypto-channel. Certain combinations of EUs can be statically
assigned to the same crypto-channel to facilitate multi-operation security processes, such as IPSec ESP
mode. When the system traffic model permits its use, static assignment can offer significant performance
improvements over dynamic assignment by avoid key and context switching per packet.
Static descriptors split the operations to be performed during a security operation into separate descriptors.
The first descriptor is typically only used to set the EU mode, and load the key and context. The second (and
20
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
Static Descriptors
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 15. Chain of Descriptors
Go to: www.freescale.com
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
DPD–DES–CTX_CRYPT
LEN_CTXIN
PTR_CTXIN
LEN_KEY
PTR_KEY
LEN_DATAIN
PTR_DATAIN
LEN_DATAOUT
PTR_DATAOUT
LEN_CTXOUT
PTR_CTXOUT
nul length
nul pointer
nul length
nul pointer
PTR_NEXT
MOTOROLA