GD32F20x User Manual
821
2) The next descriptor’s DAV bit is set. The RxDMA controller closes current descriptor
by resetting DAV bit and operation goes to Step 4.
7.
If IEEE 1588 time stamping function is enabled, the RxDMA controller writes the time
stamp value (if receiving frame meets the configured time stamping condition) to the
current descriptor’s RDES2 and RDES3. At the same time (writing timestamp value)
the RxDMA controller also writes the received frame’s status word to the RDES0 with
the DAV bit cleared and the LSG bit set.
8.
The latest descriptor is fetched by RxDMA controller. If the fetched descriptor bit 31
(DAV) is set, the RxDMA controller operation goes to Step 4. If the fetched descriptor
bit 31 is reset, the RxDMA controller enters the suspend state and sets the RBU bit in
register ENET_DMA_STAT. If flushing function is enabled, the RxDMA controller will
flush the received frame data in the RxFIFO before entering suspend state.
9.
In suspended state, there are two conditions to exit. The first is writing data in the
ENET_DMA_RPEN register by application. The second is when a new received frame
is available which means the byte number of receiving frame is greater than threshold
in Cut-Through mode or when the whole frame is received in Store-and-Forward mode.
Once exiting suspend mode, the RxDMA controller fetches the next descriptor and the
following operation goes to Step 2.
Receive descriptor fetching regulation
Descriptor fetching occurs if any one or more of the following conditions are met:
The time SRE bit is configured from 0 to 1 which makes the RxDMA controller entering
running state
The total buffer size (buffer 1 for chain mode or buffer 1 plus buffer 2 for ring mode) of
the current descriptor cannot hold the current receiving frame. In other word, the last byte
stored in buffer space is not the EOF byte
After a complete frame is transferred to buffer and before current descriptor is closed
In suspend state, the MAC received a new frame
Writing any value to receive poll enable register ENET_DMA_RPEN
Process of receiving frame
When a frame is presented on the interface, the MAC starts to receive it. At the same time,
the address filter block is running for this received frame. If the received frame fails the
address filtering it will be discarded from RxFIFO in MAC and not be forwarded to buffer by
RxDMA controller. If the received frame passes the address filtering, it will be forwarded to
buffer when the available time comes. If the RxDMA controller is configured in Cut-Through
mode, the available time means the byte number of the received frame is equal or greater
than the configured threshold. If the RxDMA controller is configured in Store-and-Forward
mode, the available time means the complete frame is stored in RxFIFO. During receiving
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...