LAN9221 Datasheet, PDF (30/151 Pages) SMSC Corporation – High-Performance 16-bit Non-PCI 10/100 Ethernet Controller with Variable Voltage I/O

3.6
High-Performance 16-bit Non-PCI 10/100 Ethernet Controller with Variable Voltage I/O
Datasheet
Destination Address Source Address ……………FF FF FF FF FF FF
00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55
00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55
00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55
00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55 00 11 22 33 44 55
…CRC
It should be noted that Magic Packet detection can be performed when LAN9221/LAN9221i is in the
D0 or D1 power states. In the D0 state, “Magic Packet” detection is enabled when the MPEN bit is
set. In the D1 state, Magic Packet detection, as well as wake-up frame detection, are automatically
enabled when the device enters the D1 state.
Checksum Offload Engines (COE)
The LAN9221/LAN9221i contains two checksum offload engines, which offload the calculation of the
16-bit checksum for transmitted and received Ethernet frames. The functionality of the checksum
offload engines is described in the following sections:
„ Receive Checksum Offload Engine (RXCOE)
„ Transmit Checksum Offload Engine (TXCOE)
3.6.1
Receive Checksum Offload Engine (RXCOE)
The receive checksum offload engine provides assistance to the CPU by calculating a 16-bit checksum
for a received Ethernet frame. The RXCOE readily supports the following IEEE802.3 frame formats:
„ Type II Ethernet frames
„ SNAP encapsulated frames
„ Support for up to 2, 802.1q VLAN tags
The resulting checksum value can also be modified by software to support other frame formats.
The RXCOE has two modes of operation. In mode 0, the RXCOE calculates the checksum between
the first 14 bytes of the Ethernet frame and the FCS. This is illustrated in Figure 3.4.
DST
T
SRC
Y
P
E
Frame Data
F
C
S
Calculate Checksum
Figure 3.4 RXCOE Checksum Calculation
In mode 1, the RXCOE supports VLAN tags and a SNAP header. In this mode the RXCOE calculates
the checksum at the start of L3 packet. The VLAN1 tag register is used by the RXCOE to indicate
what protocol type is to be used to indicate the existence of a VLAN tag. This value is typically 8100h.
Revision 2.6 (12-04-08)
30
DATASHEET
SMSC LAN9221/LAN9221i