Receive descriptor format - first word, Receive descriptor format - second word – Cirrus Logic EP93xx User Manual
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Copyright 2007 Cirrus Logic
1/10/100 Mbps Ethernet LAN Controller
EP93xx User’s Guide
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Receive Descriptor Format - First Word
Definition:
Receive Descriptor, first word. Contains the base address to the data buffer.
Bit Descriptions:
BA:
Buffer Address. This location holds the 32 bit address
pointer to the data buffer, this must point to a word aligned
location.
Receive Descriptor Format - Second Word
Definition:
Receive Descriptor, second word. Contains control, index and length for the
descriptor.
Bit Descriptions:
NSOF:
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.
BI:
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.
BL:
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.
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NSOF
BI
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