An Ethernet port received packet can be sent cut-thru to all destination ports when the following is true:
- The CPSW3_CONTROL_REG[19] CUT_THRU_ENABLE bit is
set, and
- The receive port is full duplex, and
- The Ethernet receive port speed is non-zero, and
- The packet was received on an express priority, and
- The Ethernet receive port has the remapped
received packet priority enabled via the
CPSW3_CPSW_NU_CPSW_NU_ETH_MAC_i_PN_CUT_THRU_REG[15-8]
RX_PRI_CUT_THRU_EN field, and
- All Ethernet destination ports have the remapped
packet priority enabled via the
CPSW3_CPSW_NU_CPSW_NU_ETH_MAC_i_PN_CUT_THRU_REG[7-0]
TX_PRI_CUT_THRU_EN field, and
- All Ethernet destination ports are full duplex, and
- All Ethernet destination ports are express priorities, and
- All Ethernet destination ports have a non-zero
CPSW_PN_SPEED_REG_k[3-0] SPEED, and
- All Ethernet destination ports are equal to or slower in speed than the Ethernet receive port, and
- The host port is not in the destination port list
unless the
CPSW3_CPSW_NU_CPSW_NU_CPPI_P0_CONTROL_REG[19]
CUT_MODE_ETH bit is set.
Whether or not a packet actually egresses cut-thru (with or without delay) on an Ethernet destination port depends on traffic congestion on that port. Cut-thru is compatible with Intersperced Express Traffic (IET) and Enhanced Scheduled Traffic (EST).