SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The Sum of Outflows rule is a global control that sets and clears PFC triggers on a receive port due to conditions in all other Ethernet port transmit FIFOs regardless of receive traffic. An outflow is set for a transmit FIFO priority when a PFC pause frame is received on the port with a non-zero pause quanta for that priority indicating that the port should not transmit on that priority. An outflow is clear for a priority when the transmit pause condition is removed either due to receiving a pause frame with a zero pause quanta or by the pause timer expiring for the priority. Port 0 does not have transmit flow control. The sum of outflows rule is intended to be used in some systems to pass along outflow on lower priorities with larger packet sizes. Triggering PFC on priorities due to this rule also prevents packet transmission from Ethernet ports to the host for the duration of the pause time on the triggered priorities. When configured to trigger due to this rule, pause frames will be sent on Ethernet ports regardless of receive traffic.
A PFC priority is triggered by conditions in all other Ethernet transmit FIFOs by the below equation at any time:
priX_trig_set = sum of all other Ethernet port priX_outflows >= tx_g_oflow_thresh_setX[4:0]
A PFC priority is cleared by conditions in all other Ethernet transmit FIFO’s by the below equation at any time:
priX_trig_clr = sum of all other Ethernet port priX_outflows <= tx_g_oflow_thresh_clrX[4:0]
Where,