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AT32F435/437
Series Reference Manual
2022.11.11
Page 590
Rev 2.03
6, Frame overflow
If a frame reception is aborted due to any of the following errors, this frame will not be counted:
1.
CRC error
2.
Runt frame (shorter than 64 bytes)
3.
Alignment error
4.
Length error (length field value does not match the received frame length)
5.
Out of range (frame length beyond the maximum size, untagged frame maximum size=1518 bytes,
tagged frame maximum size=1522 bytes)
6.
MII_RXER input error
26.2.3 Ethernet frame transmission and reception using DMA
The transmission and reception of the Ethernet frames are scheduled through DMA.
For transmission, the DMA reads out the Ethernet frames from the user system buffer (such as SRAM)
via the AHB master interface and forwards them to the TXFIFO. The EMAC core then transfers the data
frames in the TXFIFO to the MII/RMII interface.
For reception, the EMAC core sends the received Ethernet frames from the MII/RMII interface to the
RXFIFO so that the DMA controller reads out the Ethernet frames from the RXFIFO and transfers them
to the user data buffer (SRAM) via the AHB master interface.
DMA control and status register and descriptor table are used to manage the whole transmission and
reception process, which has its respective descriptor list. The descriptor list is usually stored in the
system buffer area (SRAM). When the transmission and reception is enabled, the DMA polls the
descriptor table through the transmit and receive poll register to start the transmission and reception
process. The base address the descriptor list for transmission and reception is stored into the transmit
descriptor list register and receive descriptor list register.
There are two descriptor structures: ring structure and chain structure. In a ring structure, each descriptor
may point to two buffers. In a chain structure (TDES0[20]=1 is configured for transmission, but
RDES1[14]=1 for reception), each descriptor points to the only one buffer. The contents of the TDES3
and RDES3 for the current frames refer to the next descriptor address for transmission and reception.
Figure 26-11 Descriptor for ring and chain structure
Descriptor 0
Descriptor 1
Descriptor 2
Descriptor n
Buffer1
Buffer2
Buffer1
Buffer2
Buffer1
Buffer2
Buffer1
Buffer2
Descriptor 1
Descriptor 2
Descriptor 0
Buffer1
Buffer1
Buffer1
Chain
Structure
Next Descriptor
Ring
Structure