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Nations Technologies Inc.
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+86-755-86309900
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Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
are transmitted, to prevent the same station from occupying PHY for a long time. Jabber timer is enabled by default.
If the Ethernet frame transmitted more than 2048 bytes, MAC will only transmit 2048 bytes and discard the exceeded
frame data.
Retransmission conflict handling mechanism
When the working mode is half-duplex, the data frame transmitted by MAC may collide. If a conflict event occurs
and only frame data of no more than 96 bytes in TxFIFO is taken out to MAC, the frame retransmission function will
be activated, and MAC will abort the current data transmission, read the data from TxFIFO and retransmit it. If a
collision event occurs and more than 96 bytes of data are taken out of TxFIFO to MAC, MAC will abort the current
transmission without activating the retransmission function and set TDES0.LC in the descriptor to notify the
application.
Status information word of frame transmit
After MAC controller frame transmission is completed, the transmission status information word is updated, which
includes a number of transmission status flags for the application. If the timestamp function is enabled, the timestamp
will be written back to the transmit descriptor along with the transmit status information word.
Clear TxFIFO operation
Regardless of whether TxFIFO is popping data into MAC, as long as ETH_DMAOPMOD.FTF is set to 1, TxFIFO
is immediately emptied and TxFIFO data pointer is reset. When receiving the clear operation command, all the data
taken out from TxFIFO to MAC will be discarded until the descriptor with TDES1.FS of 1 is received. The clear
operation will cause MAC controller to generate a data underflow event, and end the transmission of the current
frame, and return the transmission status information of the frame to the application program, and also mark the data
underflow error flag (TDES0.UF) and frame clear flag (TDES0.FF). After the DMA receives all the status
information words of the cleared frame, the clearing operation is completed, and ETH_DMAOPMOD.FTF will also
be automatically cleared to 0.
Note: If the amount of received data is large, the flash function needs to be turned on, at the same time, when the
receive overflow interrupt occurs, reset the ETH module and re-initialize the related data structure.
Transmit flow control
When ETH_MACFLWCTRL.TFE is enabled and working in full-duplex mode, MAC will automatically generate
and transmit Pause frames with CRC values when needed. When the software sets ETH_MACFLWCTRL.FCB_BPA
to 1, or RxFIFO is full, it will start to generate the Pause frame and transmit the Pause frame out. The pause time
specified by the Pause frame is the pause time value preset by the register ETH_MACFLWCTRL.
If ETH_MACFLWCTRL.FCB_BPA is set to 1 to request flow control, MAC will generate and transmit a single
Pause frame. If want to extend the pause time, or abort the pause, need to reconfigure the pause time in the
register ETH_MACFLWCTRL and request the transmission of a new Pause frame.
If transmit flow control is enabled, MAC will generate and transmit a Pause frame when RxFIFO is full. If the
RxFIFO is still full after the configured pause time is reached, MAC will transmit another Pause frame. This
process is repeated as long as RxFIFO is full. If RxFIFO is not full and the pause time has not been reached,
MAC transmits a Pause frame with a pause time of 0 to inform the remote site that the local buffer is ready to
receive new data frames.