Xilinx Virtex-4 - Page 42

42 www.xilinx.com Embedded Tri-Mode Ethernet MAC User Guide
UG074 (v2.2) February 22, 2010
Chapter 3: Client, Host, and MDIO Interfaces
R
Client Underrun
The timing of an aborted transfer is shown in Figure 3-5. An aborted transfer can occur if a
FIFO connected to the client interface empties, before a frame is completed. When the
client asserts CLIENTEMAC#TXUNDERRUN during a frame transmission, the
EMAC#PHYTXER is asserted for one clock cycle to notify the external PHY that the frame
is corrupted in MII and GMII modes. In 1000BASE-X PCS/PMA mode, the Ethernet MAC
inserts an error code (/V/) into the current frame to signal corruption. It then falls back to
idle transmission. EMAC#PHYTXER is asserted some cycles after. The client must requeue
the aborted frame for transmission.
When an underrun occurs, to request a new transmission, reassert
CLIENTEMAC#TXDVLD on the clock cycle after the CLIENTEMAC#TXUNDERRUN is
asserted.
Figure 3-5: Frame Transmission with Underrun
ug074_3_07_072705
CLIENTEMAC#TXCLIENTCLKIN
DA SA DATAL/T
CLIENTEMAC#TXD[7:0]
CLIENTEMAC#TXDVLD
EMAC#CLIENTTXACK
CLIENTEMAC#TXFIRSTBYTE
CLIENTEMAC#TXUNDERRUN
EMAC#PHYTXER
EMAC#CLIENTTXCOLLISION
EMAC#CLIENTTXRETRANSMIT
EMAC#PHYTXCHARISK
(SGMII or 1000BASE-X
PCS/PMA only)
EMAC#PHYCHARDISPMODE
(SGMII or 1000BASE-X
PCS/PMA only)
EMAC#PHYTXD[7:0]
(SGMII or 1000BASE-X
PCS/PMA only)
/T/ /R/
PRE
/S/
/V/
/I1/ /I2/ /I2/ /I2/ /I2/
FCS
DATA
SFD
/I1/
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