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Field
Name
R/W
Description
31:0
RXADDR2_RXFTSH
R/W
Receive Buffer 2 Address Pointer (Next Descriptor Address)
/ Receive 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.
RXADDR1: When RXDES0[OWN]=1 and the descriptor ring
structure is used, these bits indicate the physical address of
buffer 2. If RXDES[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
RXDES1[24]=1. When RXDES[24]=0, except when the
starting point of the frame is stored by using the value of
RXDES2, the address is generated by DMA by using the
configured value. When the address pointer points to the
buffer where the middle or last part of the frame is stored,
the DMA will ignore RXDES2[3:0], and there are no
restrictions on buffer address alignment.
RXFTSH: Before RXDES0[OWN] is cleared to zero, the
DMA will update this field with the 32 least 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 receive 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 RXDES0, RXDES1,
RXDES2 and RXDES3 are the same as those of general receive descriptor.
RXDES4 includes extended state, and RXDES6 and RXDES7 include
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.
Receive descriptor word 4 (RXDES4)
It is valid only when there is a state related to IPv4 checksum or timestamp.
Field
Name
R/W
Description
2:0
IPPT
R/W
IP payload type
If IPv4 checksum offload is activated, it indicates the payload type
encapsulated in IP datagram. These bits are "00" when there is an IP
header error or there is a segmented IP.
000: Unknown, or IP payload not processed
001
：
UDP
010
：
TCP
011
：
ICMP
1xx: Reserved
