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GD32F20x User Manual
798
(RFCEN bit in ENET_MAC_FCTL register is set), the corresponding pause control frame
function will be triggered. Whether this filter passed pause frame is forwarded to memory is
depending on the PCFRM[1:0] bit in ENET_MAC_FRMF register.
Reception process of MAC
Received frames will be pushed to the RxFIFO. The MAC strips the preamble and SFD of the
frame, and starts pushing the frame data beginning with the first byte following the SFD to the
RxFIFO. If IEEE 1588 time stamp function is enabled, the MAC will record the current system
time when a frame's SFD is detected. If the frame passes the address filter, this time stamp
is passed on to the application by writing it to descriptor.
The MAC can automatically strip PAD and FCS field data when the length/type field of
received frame is less than 1536 if APCD bit is set. MAC pushes the data of the frame into
RxFIFO up to the count specified in the length/type field, then starts dropping bytes (including
the FCS field). If the value of Length/Type field is greater than or equal to 0x600, regardless
of whether the option of automatic CRC and pad stripping function is enabled, the MAC
pushes all received frame data to Rx FIFO.
If the watchdog timer is enabled (WDD bit in ENET_MAC_CFG is reset), a frame has more
than 2048 bytes (DA + SA + LT + DATA + FCS) will be cut off receiving when has received
2048 bytes. If the watchdog timer is disabled, the MAC can extend the max receiving data
bytes to 16384(16K Bytes), any data beyond this number will be cut off.
When RxFIFO works at Cut-Through mode, it starts popping out data from RxFIFO when the
number of FIFO is greater than threshold value (RTHC bits in ENET_DMA_CTL register).
After all data of a frame pop out, receive status word is sent to DMA for writing back to
descriptor. In this mode, if a frame has started to forward to application by DMA from FIFO,
the forwarding will continue until the frame is end even if frame error is detected. Although
the error frame is not discarded, the error status will reflect in descriptor status field.
When RxFIFO works at Store-and-Forward mode (set by RSFD bit in ENET_DMA_CTL),
DMA reads frame data from RxFIFO only after RxFIFO has completed received the whole
frame. In this mode, if the MAC is configured to discard all error frames, then only valid frames
without any error can be read out from RxFIFO and forward to the application. Once the MAC
detects an SFD signal on the interface, a receive operation is started. The MAC strips the
preamble and SFD before processing the frame. The header fields are checked by filtering
and the FCS field used to verify the CRC for the frame. The frame is discarded by MAC if it
fails to pass the address filter.
Reception management of MAC
Receive operation on multi-frame handling
It is different from transmit operation, after receiving the last byte of a frame, the MAC can
judge the status of the receiving operation, so the second received frame’s forwarding is
surely followed by the first received frame data and status.
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 ...
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Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...