Receive - Realtek RTL8169 Manual

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9.1.2 Receive

The receive portion implements the receive portion of 802.3 Media Access Control. The Rx MAC retrieves packet data from the
receive portion and sends it to the Rx Buffer Manager. Additionally, the Rx MAC provides MIB control information and packet
address data for the Rx Filter. The Rx MAC supports 4-bit MII, 8-bit GMII, and 10-bit TBI interfaces to physical layer devices.
The Rx MAC can detect packets containing a 4-byte VLAN tag, and remove the VLAN tag from the received packet. If Rx
VLAN Tag Removal is enabled, then the 4 bytes following the source and destination addresses will be stripped out. The VLAN
status can be returned in the VLAN Tag field.
The Rx MAC supports IP checksum verification. It can validate IP checksums as well as TCP and UDP checksums. Packets can
be discarded based on detecting checksum errors.
The following information describes what the Rx descriptor may look like, depending on different states in each Rx descriptor.
Any Rx buffers pointed to by one of the Rx descriptors should be to at least 8 bytes in length and to 8-byte alignment in memory.
Rx Command Descriptor (OWN=1)
The driver should pre-allocate Rx buffers and configure Rx descriptors before packet reception. The following describes what
Rx descriptors may look like before packet reception.
bit
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O E
W O RSVD
N R
=
1
RSVD
RX_BUFFER_ADDRESS_LOW
RX_BUFFER_ADDRESS_HIGH
2002/03/27
VLAN_TAG VLAN Tag: The 2-byte VLAN_TAG contains information, from the
upper layer, of user priority, canonical format indicator, and VLAN ID.
Please refer to IEEE 802.1Q for more VLAN tag information.
VIDH: The high 4 bits of a 12-bit VLAN ID.
VIDL: The low 8 bits of a 12-bit VLAN ID.
PRIO: 3-bit 8-level priority.
CFI: Canonical Format Indicator.
TxBuffL
Low 32-bit address of transmit buffer
TxBuffH High 32-bit address of transmit buffer
19 18 17 16 15
T
A
V
A
13 12 8 7
Buffer_Size
VLAN_TAG
VIDL
55
6 5 4 3 2 1 0
PRIO C VIDH
FI
RTL8169
Offset 0
Offset 4
Offset 8
Offset 12
Rev.1.21