dp83820 National Semiconductor Corporation, dp83820 Datasheet - Page 19

• Manufacturer Part Number: dp83820
• Description: 10/100/1000 Mb/s Pci Ethernet Network Interface Controller
• Manufacturer: National Semiconductor Corporation

3.0 Functional Description
If 64-bit addressing is enabled, the link and bufptr fields are
64-bit fields. Otherwise, they are 32-bit fields. The
DP83820 supports an optional extended status field which
supports VLAN and IP functions. To enable the extsts field,
software should set the EXTSTS_EN bit in the CFG
register.
26-16
15-0
bit
bit
31
30
29
28
27
26
25
24
23
22
21
0004h or
0008h or
000ch or
offset
0000h
0008h
0010h
0014h
SUPCRC
INCCRC
MORE
OWN
INTR
OWC
SIZE
CRS
TXA
TFU
tag
OK
tag
TD
ED
---
cmdsts
bufptr
extsts
tag
link
Descriptor Ownership
More descriptors
Interrupt
Suppress CRC / Include
CRC
Packet OK
Descriptor Byte Count
Transmit Abort
Transmit FIFO Underrun
Carrier Sense Lost
Transmit Deferred
Excessive Deferral
Out of Window Collision
Table 3-3
Table 3-4 Transmit
32- or 64-bit "link" field to the next descriptor in the linked list. Bits 2-0 must be 0, as
descriptors must be aligned on 64-bit boundaries.
32- or 64-bit pointer to the first fragment or buffer. In transmit descriptors, the buffer can
begin on any byte boundary. In receive descriptors, the buffer must be aligned on a 64-bit
boundary.
32-bit Command/Status Field (bit-encoded)
OPTIONAL 32-bit Extended Status Field. Contains VLAN and IP information.
(Continued)
Table 3-2 DP83820 Descriptor Format
description
description
cmdsts
Common Bit Definitions
cmdsts
19
Set to 1 by the data producer of the descriptor to transfer
ownership to the data consumer of the descriptor. Set to 0 by
the data consumer of the descriptor to return ownership to
the data producer of the descriptor. For transmit descriptors,
the driver is the data producer, and the DP83820 is the data
consumer. For receive descriptors, the DP83820 is the data
producer, and the driver is the data consumer.
Set to 1 to indicate that this is NOT the last descriptor in a
packet (there are MORE to follow). When 0, this descriptor is
the last descriptor in a packet. Completion status bits are
only valid when this bit is zero.
Set to 1 by software to request a "descriptor interrupt" when
DP83820 transfers the ownership of this descriptor back to
software.
In transmit descriptors, this indicates that CRC should not be
appended by the MAC. On receives, this bit will be set based
on the RXCFG:INCCRC bit.
In the last descriptor in a packet, this bit indicates that the
packet was either sent or received successfully.
The usage of these bits differ in receive and transmit
descriptors. See below for details.
Set to the size in bytes of the data.
Transmission of this packet was aborted.
The transmit FIFO was exhausted during the transmission of
this packet.
Carrier was lost during the transmission of this packet. This
condition is not reported if TXCFG:CSI is set.
Transmission of this packet was deferred.
The length of deferral during the transmission of this packet
was excessive.
The MAC encountered an "out of window" collision during
the transmission of this packet.
Some of the bit definitions in the cmdsts field are common
to both receive and transmit descriptors:
Bit Definitions
description
usage
usage
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