Adaptec 1737100 Programmer Manual - Page 36

Number of Fragments

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AIC-6915 Ethernet LAN Controller Programmer's Manual Table 3-1. Type 0 Transmit DMA Descriptor (32-bit Addressing Only) 31 24 32 16 15 8 7 0 Skip Field (multiple of 8 bytes) One Skip Field per Packet ID = 4'b1011 I ECC NNAR T DL C R TE CN P Reserved Reserved Reserved Number Of Tx Buffers Total Packet Length First Buffer Address First Buffer Length Reserved Last Buffer Address Last Buffer Length s ID: 4 bits. This field is used by the software/debugger to identify the start of a descriptor. If a transmit DMA operation does not see a matched ID in this field, it aborts the DMA operation and sets an interrupt status bit. s Number of Fragments: 8 bits. Defines the number of follow-on segments. This field must be "nonzero". s END: Indicates that the current descriptor is at the end of the queue. The 'End" has different functionality for the following conditions: 3-6

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3-6
AIC-6915 Ethernet LAN Controller Programmer’s Manual
■
ID
: 4 bits. This field is used by the software/debugger to identify the start of a
descriptor. If a transmit DMA operation does not see a matched ID in this field, it
aborts the DMA operation and sets an interrupt status bit.
■
Number of Fragments
: 8 bits. Defines the number of follow-on segments. This field
must be “nonzero”.
■
END
: Indicates that the current descriptor is at the end of the queue. The ‘End” has
different functionality for the following conditions:
Table 3-1. Type 0 Transmit DMA Descriptor (32-bit Addressing Only)
31
24
32
16
15
8
7
0
Skip Field (multiple of 8 bytes)
One Skip Field per Packet
ID =
4’b1011
I
N
T
R
E
N
D
C
A
L
T
C
P
C
R
C
E
N
Reserved
Reserved
Reserved
Number Of Tx Buffers
First Buffer Address
Total Packet Length
First Buffer Length
Last Buffer Address
Reserved
Last Buffer Length