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3-6

AIC-6915 Ethernet LAN Controller Programmer’s Manual

■

: 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

Reserved Reserved

Reserved Number Of Tx Buffers

First Buffer Address

Total Packet Length First Buffer Length

Last Buffer Address

Reserved Last Buffer Length

1 2 ... 31 32 33 34 35 36 37 38 39 40 41 ... 189 190

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Adaptec AIC-6915 Informazioni Techniche Pagina 36