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to the end of the Ethernet frame, the CRC will not be transmitted. However,
when MAC is set to attach filling to the frame less than 60 bytes, CRC will be
attached to the end of the filling frame.
Transmit data packets
Transmission of data packets contains transmission of single data packet and
multiple data packets, and their operation mode is different.
Transmit scheduler
MAC is responsible for scheduling the frame transmission on MII. The interval
between two transmitted frames can be maintained, and the truncated binary
exponential rollback algorithm can be observed in half-duplex mode. MAC
enables transmission after meeting IFG counter and rollback delay conditions.
Transmit flow control
In full-duplex mode, when MAC_FCTRL[TXFCTRLEN]=1, MAC will generate
pause frame and transmit it when needed. The pause frame and CRC are
transmitted together. Generation of the pause frame can be enabled in two
ways. When the application program sets FCTRLB bit to 1 or the receive FIFO
is full, the pause frame will be transmitted.
Transmit FIFO refresh
FTXF bit of ETH_DMAOPMOD register controls to clear the transmit FIFO.
Even if Tx FIFO is transmitting the frame to MAC core, Tx FIFO and the
corresponding pointer will be immediately cleared to the initial state, as a result,
an underrun event will be generated to MAC transmitter, and the frame
transmission will be terminated. The state of the frame will mark both the
underrun event and the frame emptying event.
Transmit status word
After the Ethernet frame is transmitted to the MAC core and the core completes
the transmission of the frame, the transmission state will be provided to the
application program.
Transmit checksum offload
The communication protocol realizes the checksum field, which helps
understanding the integrity of data transmitted through the network. Because
encapsulating TCP and UDP on IP datagrams is the most wide application of
the Ethernet, the Ethernet controller has the function of transmitting checksum
offload, and this function supports checksum calculation and insertion in the
transmitting path, and error detection in the receiving path.