Xilinx Virtex-4 - Page 45

Embedded Tri-Mode Ethernet MAC User Guide www.xilinx.com 45
UG074 (v2.2) February 22, 2010
Client Interface
R
Frame Collisions (Half-Duplex 10/100 Mb/s Operation Only)
In half-duplex Ethernet operation, collisions occur on the medium. This is how the
arbitration algorithm is fulfilled. When there is a collision, the Ethernet MAC signals to the
client a need to have data re-supplied as follows:
• If there is a collision, the EMAC#CLIENTTXCOLLISION signal is set to 1 by the
Ethernet MAC. If a frame is in progress, the client must abort the transfer and
CLIENTEMAC#TXDVLD is deasserted to 0.
• If the EMAC#CLIENTTXRETRANSMIT signal is 1 in the same clock cycle as the
EMAC#CLIENTTXCOLLISION signal is 1, the client must resubmit the previous
frame to the Ethernet MAC for retransmission; CLIENTEMAC#TXDVLD must be
asserted to the Ethernet MAC within eight clock cycles of the
EMAC#CLIENTTXCOLLISION signal to meet Ethernet timing requirements. This
operation is shown in Figure 3-8.
Figure 3-8: Collision Handling - Frame Retransmission Required
8 Clocks
Maximum
ug074_3_10_101004
CLIENTEMAC#TXCLIENTCLKIN
CLIENTEMAC#TXD[7:0]
CLIENTEMAC#TXDVLD
EMAC#CLIENTTXACK
CLIENTEMAC#TXFIRSTBYTE
CLIENTEMAC#TXUNDERRUN
EMAC#CLIENTTXCOLLISION
EMAC#CLIENTTXRETRANSMIT
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