Transmitter AXI4-Stream AV Specifics - 9.0 English

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

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9.0 English

One of the key functions of the Ethernet AVB Endpoint is the configurable bandwidth allocation for the AV user data. Because this bandwidth is managed over time, this is done using credits which are gained when non-AV data is sent and lost, when AV data is sent with a positive or zero balance of credits enabling the AV path. When no data is present at the AV input, any credits available are removed thus preventing bursty AV traffic from getting an artificially high bandwidth. The tx_axis_av_tvalid indicates that data is available, but at the end of a frame, if another frame is available, the tx_axis_av_tvalid should remain asserted and the first byte of the new frame should be presented. This is shown in the previous figure. If tx_axis_av_tvalid is dropped between frames then any positive credit balance is lost and a negative balance remains, which results in a lower overall bandwidth allowance for the AV path.