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Ethernet AVB Endpoint User Guide www.xilinx.com 59
UG492 July 23, 2010
Tx AV Traffic I/F
Errored Legacy Frame Transmission
The legacy_tx_underrun is provided to give full backwards compatibility between the
Legacy Traffic I/F and the client interface of the Tri-Mode Ethernet MAC. The
legacy_tx_underrun provides a mechanism to inject an error into a frame before
transmission is completed. This can occur, for example, if a FIFO connected to the Legacy
client empties during transmission.
To error the frame, the legacy_tx_underrun signal may be asserted during the data
transmission or up to 1 valid clock cycle after legacy_tx_data_valid goes low.
Tx AV Traffic I/F
The signals forming the Tx AV Traffic I/F are defined in Table 5-4. All signals are
synchronous to the Tri-Mode Ethernet MAC transmitter clock, tx_clk, which must
always be qualified by the corresponding clock enable, tx_clk_en (see Table 5-1). See
(“Talker Assumptions,” page 31) for information about the expectations for the AV traffic
input to the Ethernet AVB Endpoint on this interface.
This interface is intentionally very similar to the “Tx Legacy Traffic I/F.” Note, however,
that the legacy traffic does not contain a signal that is equivalent to av_tx_done.
Additionally, the AV does not contain a signal that is equivalent to
legacy_tx_underrun: no mechanism is currently provided on the AV interface to signal
an error in a frame which is currently undergoing transmission.
X-Ref Target - Figure 6-2
Figure 6-2: Legacy Frame Transmission with Underrun
tx_clk
legacy_tx_data[7:0]
legacy_tx_data_valid
legacy_tx_ack
legacy_tx_underrun
DA SA DATAL/T
tx_clk_enable