VSC8221 datasheet(127/138 Pages) MICROSEMI

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VSC8221

Data Sheet

VMDS-10106 Revision 4.1

December 2006

127 of 132

132

31.4 SGMii 100BASE-TX Corruption of Packets with Odd Preambles

Description: in SGMii-CAT5 mode and while receiving 100BASE-TX packets with odd preambles, the VSC8221 device’s

receive rate adaptation block will not properly encode the packet.

The following diagram is an excerpt from Figure 2 of the Cisco SGMii Specification v1.7.

Figure 32. SGMii Rx Path from the PHY to the MAC

impact: This will cause a normal packet with an odd preamble to become corrupted. The corruption occurs while encoding the

SFD. This may cause an otherwise normal packet to be dropped at the MAC.

Example:

Case i : even preamble (correct)

55555Dxyz : encoded as 55, 55, D5, yx …

Case ii : odd preamble (incorrect)

5555Dxyz : encoded as 55, 55, xD, zy …

Note no SFD in above

Workaround: There is no workaround at the physical layer of the PHY’s packet transmission. if higher layers are being

employed on this receive path such as TCP/iP, then a re-transmission request could occur to recover from the loss. This is a

problem only when the preamble is corrupted by noise in the CAT5 link or when the link partner PHY is transmitting a non-

compliant preamble.

31.5 SGMii 100BASE-TX Corruption of Packets with no ESDs

Description: in SGMii-to-CAT5 mode and while receiving 100BASE-XT packets with no ESD from the CAT5 interface, the

100BASE-TX receive PCS extends the packet by a nibble while asserting RX_ER.

impact: The rate adaption block subsequently will not transmit this additional nibble and the RX_ER to the MAC. The MAC may

then consider this a normal packet.

Workaround: There is no workaround at the PHY’s SGMii layer. The likelihood of receiving a packet with no ESD and no CRC

error is low. During such an event (if it does occur), the data address and payload are not corrupted. The only item that would

be lost is that an RX_ER event occurred to mark the missing ESD during transmission.

For more information, see Figure 32, above.

Serializer

PCS

Transmit

State

Machine

ENC_RXD [0:9]

RX_ER

RXD[7:0]

RX_CLK @ 25 MHz

PHY

Receive

Rate

Adaptation

RXD[3:0] for 10/100BT

RXD[7:0] for 1000BT

RX_CLK @ 2.5/25/125 MHz

To MAC

From CAT-5

VSC8221 Datasheet(PDF) 127 Page - Microsemi Corporation

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