TX AV Traffic Interface - 9.0 English

Tri-Mode Ethernet MAC LogiCORE IP Product Guide (PG051)

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9.0 English

The AV traffic interface is intended for the Quality of Service audio/video data. The Ethernet AVB Endpoint gives priority to the AV traffic interface over the legacy traffic interface, as dictated by IEEE 802.1Q 75% bandwidth restrictions. The signals forming the TX AV Traffic interface are defined in Table 3. The timing of this interface is exactly the same as that of the TX Legacy Traffic with the only difference being how the tvalid signal is handled between frames.

In the following figure, the end of frame transmission, the tx_axis_av_tvalid signal is held High, which indicates to the Credit-Based Traffic Shaping Algorithm that another AV frame is queued. Unless the configurable bandwidth restrictions have been exceeded, this parks the Credit-Based Traffic Shaping Algorithm onto the AV traffic queue and the following frame can immediately be taken. However, if no further AV traffic frames are queued, the tx_axis_av_tvalid signal should be set to Low immediately following the end of frame transmission. This then allows the Credit-Based Traffic Shaping Algorithm 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 Credit-Based Traffic Shaping Algorithm switches to service the legacy traffic regardless of the state of the tx_axis_av_tvalid signal.

Figure 1. TX AV Traffic Timing