AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 17

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

5.3 Done Notification Bit
The done notification bit in the MPC184 descriptor header acts as a manual override to the crypto-channel
configuration register’s NOTIFICATION_TYPE bit. The NOTIFICATION_TYPE bit determines whether
the MPC184 will advise the system (via interrupt or header writeback) that it is DONE with an operation
after every descriptor, or after a chain of descriptors. Setting the notification bit in the descriptor header is
unnecessary and redundant if NOTIFICATION_TYPE is set to ‘end-of-descriptor,’ but if set to
‘end-of-chain,’ the notification bit in the header can be quite useful as an intermediate notification.
The DONE notification can take the form of an interrupt or modified header writeback or both, depending
on the state of the INTERRUPT_ENABLE and WRITEBACK_ENABLE control bits in the crypto-channel
configuration register.
When the channel signals DONE via header writeback, the least significant byte (little endian) of the
original header (at its original location in system memory) will always read as set to 0xFF, and the remaining
24 bits will not be modified. MPC184-initiated PCI writes can occur only on 64-bit word boundaries, but
reads can occur on any byte boundary. Writing back a header read from a non-64-bit word boundary will
yield unpredictable results.
6 Descriptor Length and Pointer Fields
The length and pointer fields represent one of seven data length/pointer pairs. Each pair defines a block of
data in system memory. The length field gives the length of the block in bytes. The maximum allowable
number of bytes is 32 Kbytes. A value of zero loaded into the length field indicates that this length/pointer
pair should be skipped and processing continue with the next pair.
The pointer field contains the address, in PCI address space, of the first byte of the data block. Transfers
from the PCI bus with the pointer address set to zero will have the length value written to the EU, and no
data fetched from the PCI bus.
MOTOROLA
Certain public key operations require information about data length, but
not the data itself. Figure 12 shows the descriptor length field.
Out-FIFO
In-FIFO
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MPC184 Descriptor Programmer’s Guide— PCI View
Freescale Semiconductor, Inc.
In-Snooping
For More Information On This Product,
In-FIFO
Go to: www.freescale.com
MDEU
Figure 11. Snooping
NOTE
Out-FIFO
In-FIFO
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Out-Snooping
Descriptor Length and Pointer Fields
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