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Chapter 6: Ethernet AVB Endpoint Transmission
X-Ref Target - Figure 6-3
av_tx_data_valid
av_tx_done
av_tx_ack
Figure 6-3
frame transmission, it places the first column of data onto the av_tx_data[7:0] port
and asserts a logic 1 onto av_tx_valid.
After the Ethernet AVB Endpoint core reads the first byte of data, it asserts the av_tx_ack
signal. On the next and subsequent rising clock edges, the client must provide the
remainder of the data for the frame. The end of frame is signalled to the core by taking the
av_tx_valid to logic 0.
In
which indicates to the
configurable bandwidth restrictions have been exceeded, this parks the
the AV traffic queue.
signal to request a subsequent frame, and the frame transmission cycle of
repeats. However, if no further AV traffic frames are queued, the av_tx_done signal
should be set to logic 1 immediately following the end of frame transmission. This than
allows the
queued).
If, following the end of frame reception, the bandwidth allocation for AV traffic has been
exceeded, the
the av_tx_done signal.
For this reason, the av_tx_done signal should be considered an aid to the
help make best use of the available network bandwidth. Asserting this signal after all AV
traffic has been serviced immediately allows the
This helps achieve in excess of the 25% minimum allocation for the legacy traffic. However,
holding off the assertion of av_tx_done will not act as cheat mode to exceed the
maximum bandwidth allocation for the AV traffic.
60
tx_clk
tx_clk_enable
av_tx_data[7:0]
Figure 6-3: Normal Frame Transmission across the AV Traffic Interface
illustrates the timing of a normal frame transfer. When the AV client initiates a
Figure
6-3, following the end of frame transmission, the av_tx_done signal is held low,
"Tx Arbiter"
Figure 6-3
"Tx Arbiter"
to schedule legacy traffic transmission (if any legacy frames are
"Tx Arbiter"
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that another AV frame is queued. Unless the
then illustrates the client asserting the av_tx_valid
switches to service the legacy traffic regardless of the state of
"Tx Arbiter"
L/T
DATA
"Tx Arbiter"
Figure 6-3
"Tx Arbiter"
to service the legacy traffic.
Ethernet AVB Endpoint User Guide
UG492 September 21, 2010
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