Motorola ColdFire MCF5281 User Manual page 407

Table 17-37. Transmit Buffer Descriptor Field Definitions (continued)
Word Location
Offset + 2 Bits [15:0]
Offset + 4 Bits [15:0]
Offset + 6 Bits [15:0]
1
The transmit buffer pointer, which contains the address of the associated data buffer, must always be evenly
divisible by 4. The buffer must reside in memory external to the FEC. This value is never modified by the
Ethernet controller.
Once the software driver has set up the buffers for a frame, it
should set up the corresponding BDs. The last step in setting up
the BDs for a transmit frame should be to set the R bit in the
first BD for the frame. The driver should follow that with a
write to TDAR which will trigger the FEC to poll the next BD
in the ring.
MOTOROLA
Field Name
Data Length Data Length, written by user.
Data length is the number of octets the FEC should transmit
from this BD's data buffer. It is never modified by the FEC. Bits
[15:5] are used by the DMA engine, bits[4:0] are ignored.
A[31:16] Tx data buffer pointer, bits [31:16]
A[15:0] Tx data buffer pointer, bits [15:0].
NOTE
Chapter 17. Fast Ethernet Controller (FEC)
Buffer Descriptors
Description
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