Tx AV Traffic I/F

Errored Legacy Frame Transmission

tx_clk

tx_clk_enable

legacy_tx_data[7:0]

legacy_tx_data_valid

legacy_tx_ack

legacy_tx_underrun

DA

SA

L/T

DATA

Figure 6-2:Legacy Frame Transmission with Underrun

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.

Ethernet AVB Endpoint User Guide

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UG492 July 23, 2010

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Xilinx UG492 manual Tx AV Traffic I/F, Errored Legacy Frame Transmission