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5.0 Buffer Management
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DP83816
5.1.3 Multiple Descriptor Packets
A single packet may also cross descriptor boundaries. This
is indicated by setting the MORE bit in all descriptors
except the last one in the packet. Ethernet applications
(bridges, switches, routers, etc.) can optimize memory
utilization by using a single small buffer per receive
descriptor, and allowing the DP83816 hardware to use the
minimum number of buffers necessary to store an
incoming packet.
5.1.4 Descriptor Lists
Descriptors are organized in linked lists using the link field.
The system designer may also choose to implement a
"ring" of descriptors by linking the last descriptor in the list
back to the first. A list of descriptors may represent any
number of packets or packet fragments.
Figure 5-2 Multiple Descriptor Packets
Figure 5-3 List and Ring Descriptor Organization
link
ptr
MAC hdr
netwk hdr
data
1
14
multiple descriptor / single fragment
link
ptr
1
20
link
ptr
0
30
10180
addr 10140
10140
addr 10100
101C0
addr 10180
10100
addr 101C0
Descriptors Organized in a Ring
10180
addr 10140
10140
addr 10100
101C0
addr 10180
00000
addr 101C0
Descriptors Organized in a Linked List
Summary of Contents for MacPHYTER-II DP83816
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