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Field
Name
R/W
Description
31:0
TXADDR2_TXFTSH
R/W
Transmit Buffer 2 Address Pointer (Next descriptor address)
/ Transmit frame timestamp high
It indicates the location of the data in the memory to the
DMA. When all data have been transmitted, the DMA can
use these bits to return the timestamp data.
TXADDR2: When TXDES0[31]=1 and the descriptor ring
structure is used, these bits indicate the physical address of
buffer 2. If TXDES1[24]=1, this address contains the pointer
of the physical register where the next descriptor is located.
The buffer address pointer matches the bus width only when
TXDES1[24]=1.
TXFTSH: Before TXDES0[31] is cleared to zero, the DMA
will update this field with the 32 most significant bits of the
timestamp captured for the corresponding transmitted
frame. The bit field contains a timestamp only when the
timestamp function of this frame is activated and LS=1.
Functional description of enhanced transmit descriptor
If the timestamp or IPv4 checksum offload is activated, the enhanced descriptor
must be used. The enhanced descriptor consists of eight 32-bit words, which is
twice the normal size of the descriptor. Definitions of TXDES0, TXDES1,
TXDES2 and TXDES3 are the same as those of general transmit descriptor.
TXDES6 and TXDES7 contain the timestamp.
When selecting the enhanced descriptor mode, 32-byte memory need to be
allocated for each descriptor. If the timestamp or IPv4 checksum offload is not
used, the enhanced descriptor format can be disabled, and the software can
use a general descriptor with a default size of 16 bytes.
Transmit descriptor word 4 (TXDES4)
Field
Name
R/W
Description
31:0
Reserved
Transmit descriptor word 5 (TXDES5)
Field
Name
R/W
Description
31:0
Reserved
Transmit descriptor word 6 (TXDES6)
Field
Name
R/W
Description
31:0
TXFTSL
R/W
Transmit Frame Timestamp Low
This bit field will be updated by the DMA with the 32 least significant bits
of the timestamp captured for the corresponding transmitted frame. The
bit field contains a timestamp only when LS=1.
Transmit descriptor word 7 (TXDES7)