DP83821 datasheet(24/86 Pages) NSC

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3.0 Functional Description (Continued)

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Figure 3-12 Ring Descriptor Organization

3.13.2.4 Descriptor Lists

Descriptors may also be organized in linked lists using the

link field. The linked list may be terminated by either a

NULL link field, or by using the descriptor OWN bit. A list of

descriptors may represent any number of packets or

packet

fragments.

Care

should

used

when

implementing a linked list terminated by a NULL link as

there is a potential for driver software and the device to get

out of sync. Before clearing a link field when freeing up

descriptors, the driver should verify that the device has

already traversed the link.

Figure 3-13 Linked List Descriptor Organization

10180

addr 10140

10140

addr 10100

101C0

addr 10180

10100

addr 101C0

Descriptors Organized in a Ring (Recommended Method)

10180

addr 10140

10140

addr 10100

101C0

addr 10180

addr 101C0

Linked List terminated by OWN bit

10180

addr 10140

10140

addr 10100

101C0

addr 10180

00000

addr 101C0

Linked List terminated by NULL link field

own

!own

own

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