DP83821 datasheet(68/86 Pages) NSC

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4.0 Register Set (Continued)

4.2.33 Receive Descriptor Pointer 3 Register

This register points to the Receive Descriptor for Priority Queue 3 (highest priority).

4.2.34 VLAN/IP Receive Control Register

This register allows enabling of the various VLAN tag handling features and IP Checksum offload features.

Tag: RXDP3

Size: 32 bits

Hard Reset: 00000000h

Offset: 00B8h

Access: Read Write

Soft Reset: 00000000h

bit

tag

description

usage

31-3

RXDP3

Receive

Descriptor Pointer

The current value of the receive descriptor pointer for Priority Queue 3. Packets will be

stored in Priority Queue 3 based on the number of priority queues enabled and the

priority field in the VLAN tag. When the receive state machine is idle, software must set

RXDP3 to the address of an available receive descriptor, and then enable the queue by

writing to the RXE bit in the CR with the RXPRI[3] bit set. While the receive state machine

is active, RXDP3 will follow the state machine as it advances through a linked list of

available descriptors. If the link field of the current receive descriptor is NULL (signifying

the end of the list), RXDP3 will not advance, but will remain on the current descriptor. Any

subsequent writes to the RXE bit of the CR register will cause the receive state machine

to reread the link field of the current descriptor to check for new descriptors that may have

been appended to the end of the list. Software should not write to this register unless the

receive state machine is idle. Receive descriptors must be aligned on 64-bit boundaries

(A2-A0 must be zero).

2-0

unused

Tag: VRCR

Size: 32 bits

Hard Reset: 00000000h

Offset: 00BCh

Access: Read Write

Soft Reset: 00000000h

bit

tag

description

usage

31-8

unused

RUDPE

Reject UDP

Checksum Errors

When set to 1, all packets with UDP headers that have errors in the UDP checksum field

will be rejected. If IPEN is 0, this bit will be ignored.

RTCPE

Reject TCP

Checksum Errors

When set to 1, all packets with TCP headers that have errors in the TCP checksum field

will be rejected. If IPEN is 0, this bit will be ignored.

RIPE

Reject IP

Checksum Errors

When set to 1, all packets with IP headers that have errors in the IP checksum field will

be rejected. If IPEN is 0, this bit will be ignored.

IPEN

IP Checksum

Enable

When set to a 1, the receiver will detect IP, TCP, and UDP headers, and validate the

checksum fields.

DUTF

Discard Untagged

Frames

Receiver will discard any frames without a1 VLAN tag.

DVTF

Discard VLAN

Tagged Frames

Receiver will discard any frames with a VLAN tag.

VTREN

VLAN Tag

Removal Enable

Enables stripping of the VLAN tag upon detection. If VTDEN is not set, then this bit will

have no effect.

VTDEN

VLAN Tag

Detection Enable

Enable detection of VLAN packets based on VLAN type field as configured in the VLAN

Data Register. VLAN status, including user_priority, CFI and VID fields, will be posted in

the EXTSTS field of the receive packet descriptor.

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