Cirrus Logic EP93xx - Manual (Page 332)

9-30 DS785UM1
Copyright 2007 Cirrus Logic
1/10/100 Mbps Ethernet LAN Controller
EP93xx User’s Guide
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TBL: Transmit Buffer Length. This field contains the byte count
of the number of bytes in the transmit buffer. There are no
restrictions on the actual buffer size. If the length is set to
zero, the descriptor will be ignored. A frame may not be
terminated with a zero length buffer.
9.2.3.10 Transmit Status Queue
The Transmit Status queue is used to pass transmit status from the MAC to the Host. In
operation the status queue is similar to the transmit descriptor queue, it is a circular queue in
contiguous memory space. The location and size of the queue are set at initialization by the
Host writing to the Transmit Status Queue Base Address, and the Transmit Status Queue
Base Length registers. The base address must point to a word aligned memory location. The
length is set to the actual status queue length in bytes. This should be an integral number of
status entries and should not exceed 64 Kbytes total. The Current Address must be set to
point to the first status entry to be used. This would normally be the first entry in the queue
(same value as the base address).
The Host needs to ensure that in operation there is always room in the status queue for any
transmit frame which is enqueued in the transmit descriptor queue.