Flow Control Basics - 9.0 English

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

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9.0 English

A MAC can transmit a Pause Control frame to request that its link partner cease transmission for a specific period of time. For example, the left MAC in the previous figure can initiate a pause request when its user FIFO (illustrated) reaches a nearly full state.

A MAC should respond to received Pause Control frames by ceasing transmission of frames for the period defined in the received pause control frame. For example, the right MAC of the previous figure can cease transmission after receiving the Pause Control frame transmitted by the left MAC. In a well designed system, the right MAC ceases transmission before the user FIFO of the left MAC overflows to provide time to empty the FIFO to a safe level before resuming normal operation. This practice safeguards the system against FIFO overflow conditions and frame loss.