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AT32F435/437
Series Reference Manual
2022.11.11
Page 596
Rev 2.03
TDES2: Transmit descriptor word2
TDES2 contains the address pointer to the first buffer of the descriptor or it contains the lower 32-bit time
stamp data.
Bit
Name
Type
Description
Bit 31: 0
TBAP1/T
TSL
rw
Transmit buffer 1 address pointer / Transmit frame time stamp low
This field has two functions:
1: The application indicates to the DMA the location of the Ethernet data in system
memory.
2: After all data are transferred, the DMA can use these bits to store the time stamp
of the transmit frame.
TBAP1
When the current descriptor is owned by the DMA, these bits indicate the physical
address of the buffer 1.
TTSL
Before it releases the descriptor to the CPU, the DMA writes the 32 least significant
bits of the time stamp capture for the corresponding transmit frame to this field. This
field has the time stamp only when the TTSE bit in the TDES0 and the LS bit for the
frame are set.
TDES3: Transmit descriptor word3
TDES3 contains the address pointer to the second buffer of the descriptor or the next descriptor, or it
contains time stamp data.
Bit
Name
Type
Description
Bit 31: 0
TBAP2/T
TSH
rw
Transmit buffer 2 address pointer (Next descriptor address) / Transmit frame time
stamp high
This field has two functions:
1: The application indicates to the DMA the location of the Ethernet data in system
memory.
2: After all data are transferred, the DMA can use these bits to store the 32 most
significant bits of the time stamp for the frame.
TBAP2
When the current descriptor is owned by the DMA, these bits indicate the physical
address of buffer2 if a descriptor ring structure is used. If a descriptor chain structure
is used, these bits indicate the physical address of the next descriptor.
TTSH
Transmit frame time stamp high
The DMA updates these bits with the 32 most significant bits of the time stamp
captured for the corresponding frame. This field has the time stamp only when the
TTSE bit in the TDES0 and the LS bit for the frame are set.
RXDMA configuration
1.
The application sets up receive descriptors (RDES0~RDES3), sets the OWN bit and then releases
the descriptors to the DMA.
2.
When the SSR bit (EMAC_DMAOPM[1]) is set, the DMA enters run state and attempts to acquire
receive descriptors. If the fetched descriptor is not free (owned by the CPU), the DMA enters
suspend state and jumps to Step 9.
3.
The DMA decodes the receive buffer address from the acquired receive descriptors.
4.
The DMA writes the frame data in the RXFIFO to the receive buffer.
5.
When the buffer is full or the frame transfer ends, the receive controller will fetch the next
descriptor from the descriptor queue.
6.
If the current frame transfer is complete, the DMA jumps to Step 7. If the OWN bit of the next
receive descriptor is cleared while the current frame is not complete (EOF is not received), when
the frame flushing function is enabled, the DMA sets the descriptor error bit in the RDES0, closes
the current descriptor (OWN=0) and sets the LS bit in the RDES1, and then jumps to Step 8 (Note
that the LS bit in the RDES1 will not be set if the frame flushing feature is disabled). When the
OWN bit of the next descriptor is set while the current frame transfer is not complete, the DMA
then closes the current descriptor, marks it as intermediate and jumps to Step 4.
7.
If IEEE1588 time stamp is enabled, the DMA writes the time stamp to the current descriptor’s
RDES2 and RDES3 while it writes the status word to the RDES0, with the OWN bit cleared and
the LS bit set.