Technical information

3-8
AIC-6915 Ethernet LAN Controller Programmer’s Manual
■
Total Packet Length
: This 16-bit field defines the total packet length. If this field is
zero, it is ignored and the total packet length is equal to the sum of all the buffers. If
this field is nonzero, it is defined as the total packet length.
Note:
In Novell TCB/ECB blocks, the total packet length is not always equal to the
sum of the buffer length. Transmit DMA pads extra bytes to the FIFO if the total
packet length is greater than the sum of the buffer length.
■
Buffer Length
: The length of the host buffer in bytes.
■
Buffer Address
: The byte address of the host buffer.
Type 1 (Generic), 32-bit Addressing Mode (Buffer Descriptor)
In Type 1 and 2 buffer descriptors, the INTR, END, CALTCP, CRCEN, and Number of Tx
Buffers fields are valid for the first buffer of a frame only. The ID, Length, and Address are
valid for all buffers of the frame. The software driver must use the ‘End’ bit only in the
first buffer descriptor of a frame. The queue wraps around after reading 8 bytes of
descriptor data for Type 1 and 16 bytes of data for Type 2.
Type 2 (Generic), 64-bit Addressing Mode (Buffer Descriptor)
In Type 1 and 2 buffer descriptors, the INTR, END, CALTCP, CRCEN, and Number of Tx
Buffers fields are valid for the first buffer of a frame only. The ID, Length, and Address are
valid for all buffers of the frame. The software driver must use the ‘
E
ND
’ bit only in the
first buffer descriptor of a frame. The queue wraps around after reading 8 bytes of
descriptor data for Type 1 and 16 bytes of data for Type 2.
Table 3-4. Type 1 Transmit DMA Descriptor (32-bit Addressing)
31 24 23 16 15 8 7 0
Skip Field (multiple of 8 bytes)
One Skip Field per Buffer
ID =
4’b1011
I
N
T
R
E
N
D
C
A
L
T
C
P
C
R
C
E
N
Number Of Tx Buffers
(valid only if first
fragment)
Length (bytes)
Address