AN2492 Freescale Semiconductor / Motorola, AN2492 Datasheet - Page 18

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

Descriptor Length and Pointer Fields
Descriptor Length and Pointer Fields
Table 12 shows the descriptor length field mapping.
Figure 13 shows the descriptor pointer field
Table 13 shows the descriptor pointer field mapping.
Following the length/pointer pairs is the next descriptor field, which contains the pointer to the next
descriptor in memory. On completion of processing of the current descriptor, this value, if non-zero, is used
to request a PCI burst read of the next-data-packet descriptor. This automatic load of the next descriptor is
referred to as descriptor chaining. Figure 14 displays the next descriptor pointer field.
18
31:16 —
15:0
31:0
Bits
Bits
Reset
Reset
Field
Field
R/W
R/W
Data field length
Data field pointer
31
31
Name
Name
MPC184 Descriptor Programmer’s Guide— PCI View
Reset Value
Reset Value
Freescale Semiconductor, Inc.
Table 13. Descriptor Pointer Field Mapping
Table 12. Descriptor Length Field Mapping
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0
0
0
Reserved
Figure 13. Descriptor Pointer Field
Figure 12. Descriptor Length Field
Reserved, set to zero
Note: The maximum length this field can be set to 32 Kbytes. Under host
control, a channel can be temporarily locked static, and ‘data only’
descriptors can be chained to fetch blocks larger than 32 Kbytes in
32-Kbyte sub-blocks without key/context switching, until the large original
block has been completely ciphered. Length fields also indicate the size of
items to be written back to memory on completion of security processing in
the MPC184.
The data pointer field contains the address, in PCI address space, of the
first byte of the data packet for either read or writeback. Transfers from the
PCI bus with pointer address set to zero will be skipped.
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.
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.
Data Field X Pointer
R/W
R/W
0
0
16
Description
Description
WARNING
15
Data Length Field
MOTOROLA
0
0