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Ethernet AVB Endpoint User Guide
UG492 September 21, 2010
Chapter 6:
Ethernet AVB Endpoint Transmission
Figure 6-3
illustrates the timing of a normal frame transfer. When the AV client initiates a
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
Figure 6-3
, following the end of frame transmission, the
av_tx_done
signal is held low,
which indicates to the
“Tx Arbiter”
that another AV frame is queued. Unless the
configurable bandwidth restrictions have been exceeded, this
parks
the
“Tx Arbiter”
onto
the AV traffic queue.
Figure 6-3
then illustrates the client asserting the
av_tx_valid
signal to request a subsequent frame, and the frame transmission cycle of
Figure 6-3
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
“Tx Arbiter”
to schedule legacy traffic transmission (if any legacy frames are
queued).
If, following the end of frame reception, the bandwidth allocation for AV traffic has been
exceeded, the
“Tx Arbiter”
switches to service the legacy traffic regardless of the state of
the
av_tx_done
signal.
For this reason, the
av_tx_done
signal should be considered an aid to the
“Tx Arbiter”
to
help make best use of the available network bandwidth. Asserting this signal after all AV
traffic has been serviced immediately allows the
“Tx Arbiter”
to service the legacy traffic.
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.
X-Ref Target - Figure 6-3
Figure 6-3:
Normal Frame Transmission across the AV Traffic Interface
tx_clk
av_tx_data[7:0]
av_tx_data_valid
av_tx_done
av_tx_ack
DA
SA
DATA
L/T
tx_clk_enable
DA
Содержание LogiCORE Endpoint v2.4
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Страница 22: ...22 www xilinx com Ethernet AVB Endpoint User Guide UG492 September 21 2010 Preface About This Guide...
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Страница 102: ...102 www xilinx com Ethernet AVB Endpoint User Guide UG492 September 21 2010 Chapter 10 Configuration and Status...