Method - 9.0 English

1. Choose a RX priority 0 FIFO nearly-full occupancy threshold (7/8 occupancy is used in this description but the choice of threshold is implementation-specific). When the FIFO exceeds this occupancy, assert the XOFF request signal to initiate a PFC frame with priority 0 enabled and 0xFFFF used as the priority 0 pause_quantum duration (0xFFFF is the default value of the priority 0 quanta register). This is the maximum pause duration. This causes the left-hand MAC to transmit a PFC frame, which in turn causes the right-hand MAC to assert its rx_pfc_p0_tvalid to request that the TX priority 0 FIFO on the right-hand side stops transmission. If the client logic of the left-hand MAC continues to be unable to service the RX priority 0 FIFO then the left-hand Ethernet MAC automatically re-sends the PFC frame each time 0xFF00 quanta expires (this is the default value of the priority 0 refresh), that is, before the previously sent quanta has expired.
2. Choose a RX priority 0 FIFO occupancy threshold (3/4 is used in this description but the choice of threshold is implementation-specific). When the occupancy of the FIFO falls below this occupancy, send an XON request by de-asserting the tx_pfc_p0_tvalid signal. If the TX auto XON feature is enabled this initiates a PFC frame with priority 0 enabled and the priority 0 quanta set to 0x0000. This indicates a zero pause duration (XON), and upon receiving this PFC frame, the right-hand MAC de-asserts the rx_pfc_p0_tvalid allowing the TX priority 0 FIFO on the right to resume transmission (it does not wait for the original requested quantum duration to expire). If the TX auto XON feature is not enabled then no PFC frame is sent and transmission does not restart until the requested quantum duration has expired.