AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 19

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

Table 14 describes the descriptor pointer field mapping.
7 Descriptor Chaining
Descriptor chaining provides a measure of decoupling between host CPU activities and the status of the
MPC184. Rather than waiting for the MPC184 to signal DONE, and arbitrating for the PCI bus in order to
write directly to the next-data-packet descriptor in the crypto-channel, the host can simply create new
descriptors in memory, and chain them to descriptors which have not yet been fetched by the MPC184 by
filling the next-data-packet field with the address of the newly created descriptor. Whether or not processing
continues automatically following next-descriptor fetch and whether or not an interrupt is generated
depends on the programming of the crypto-channel’s configuration register.
See Section 7.1.1, “Crypto-Channel Configuration Register (CCCR),” in the MPC184 Security
Co-Processor User’s Manual, PCI Interface, for additional information on how the MPC184 can be
programmed to signal and act on completion of a descriptor.
Figure 15 shows a conceptual chain, or linked list, of descriptors.
MOTOROLA
Bits
31:0
Reset
Field
R/W
Next descriptor
pointer
31
Name
It is possible to insert a descriptor into an existing chain; however, great
care must be taken when doing so.
MPC184 Descriptor Programmer’s Guide— PCI View
Reset Value
Freescale Semiconductor, Inc.
Table 14. Descriptor Pointer Field Mapping
For More Information On This Product,
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Figure 14. Next Descriptor Pointer Field
Go to: www.freescale.com
The next descriptor pointer field contains the address, in PCI address
space, of the next descriptor to be fetched if descriptor chaining is
enabled.
The next descriptor pointer address must be modulo-8
aligned if writeback is enabled as the method of DONE
notification.
Next Descriptor Pointer
NOTE
R/W
0
Description
WARNING
Descriptor Chaining
0
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