Xilinx IP Ethernet AVB Endpoint v2.4 UG492 - Manual (Page 59)

Ethernet AVB Endpoint User Guide www.xilinx.com 59
UG492 September 21, 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 DATA L/T
tx_clk_enable