Cirrus Logic EP93 Series User Manual page 317

Receive Descriptor Format - First Word
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Definition:
Receive Descriptor, first word. Contains the base address to the data buffer.
Bit Descriptions:
BA:
Receive Descriptor Format - Second Word
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NSOF
15 14 13 12
Definition:
Receive Descriptor, second word. Contains control, index and length for the
descriptor.
Bit Descriptions:
NSOF:
BI:
BL:
DS785UM1
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BA
11 10 9 8
BA
Buffer Address. This location holds the 32 bit address
pointer to the data buffer, this must point to a word aligned
location.
27 26 25 24
11 10 9 8
BL
Not Start of Frame. When the Not Start Of Frame bit is set
in a descriptor, the associated buffer will only be used for a
frame being continued from another buffer. If there is not a
frame to be continued (that is, start of a new frame), the
buffer will be discarded. When a buffer is discarded in this
manner, there is no status posted.
Buffer Index. The buffer index is provided for Host
software purposes. The MAC keeps an internal copy of the
index and includes it with any status writes associated with
a receive buffer.
Buffer Length. The Buffer Length contains the number of
bytes available to be used in the receive buffer. This
should be an integral number of words. If the length is set
to zero, the descriptor will be ignored and no status will be
posted for the buffer.
Copyright 2007 Cirrus Logic
1/10/100 Mbps Ethernet LAN Controller
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7 6 5 4
23 22 21 20
BI
7 6 5 4
EP93xx User's Guide
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3 2 1 0
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