GD32F20x User Manual
791
Transmission management of MAC
Jabber timer
In case of one station occupies the PHY for a long time, there is a jabber timer designed for
cutting off the frame whose length is more than 2048 bytes. By default, jabber timer is enabled
so when application is transmitting a frames whose byte length is more then 2048, the MAC
will only transmit 2048 bytes and drop the last ones.
Collision condition solve mechanism
– Re-transmission
When the MAC is running under Half-duplex mode, collision may happen when MAC is
transmitting frame data on interface. When no more than 96 bytes data popped from FIFO
towards MAC and collision condition occurs, the re-transmission function is active. In this
case, MAC will stop current transmitting and then read frame data from FIFO again and send
them on interface again. When more than 96 bytes data popped from FIFO towards MAC and
collision condition occurs, MAC will abort transmitting current frame data and not re-transmit
it. Also MAC will set late collision flag in descriptor to inform application.
Transmit status word
Transmit status word includes many transmit state flags for application and are updated after
the complete the transmission of the frame. If timestamp function is enable, the timestamp
value is also write back to transmit descriptor along with transmit status.
Transmit FIFO flush operation
Application can clear TxFIFO and reset the FIFO data pointer by setting FTF bit (bit 20) of
ENET_DMA_CTL register. The flush operation will be executed at once no matter whether
TxFIFO is popping data to MAC. This results in an underflow event in the MAC transmitter,
and the makes frame transmission abort. At the same time, MAC returns state information of
frame and transmit status words transferred to the application. The status of such a frame is
marked with both underflow and frame flush events (TDES0 bits 1 and 13). When the transmit
data in TxFIFO is flushed, the transmit status word will be written back to descriptor. After the
status is written, the flush operation is complete. When a flush operation is received, all the
following data which should be popped from TxFIFO into MAC will be dropped unless a new
FSG bit of descriptor is received. After operation completed, the FTF bit of ENET_DMA_CTL
register is then automatically cleared.
Transmit flow control
The MAC manages transmission frame through back pressure (in Half-duplex mode) and the
pause control frame (in Full-duplex mode) for flow control.
Half-duplex mode flow control : Back Pressure
When MAC is configured in Half-duplex mode, there are two conditions to trigger the back
pressure feature. Both of the two conditions are triggered to enable back pressure function
which is implemented by sending a special pattern (called jam pattern) 0x5555 5555 once to
Содержание GD32F20 Series
Страница 1: ...GigaDevice Semiconductor Inc GD32F20x ARM Cortex M3 32 bit MCU User Manual Revision 2 2 Oct 2019 ...
Страница 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Страница 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Страница 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Страница 385: ...GD32F20x User Manual 385 ...
Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...