727
/
838
Nations Technologies Inc.
Tel
:
+86-755-86309900
:
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
32 bits of timestamp respectively (TxDMA controller will write the timestamp into TDES2 and TDES3 after frame
transmission is completed. And at the same time, set TDES0.TTSS to 1 to mark timestamp of current frame as
recorded). Each bit is defined and described in detail as follows:
Note: If a frame is described by multiple descriptors, the control bits for descriptors (except TDES1.IC) are only
valid for first descriptor. Status information and time stamps (if time stamping is enabled) are only written back to
last descriptor.
Table 25-8 Transmit descriptor overview
Register
31
30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
TDES0
OWN
Status bits
TDES1
Control bits
Buffer 2 bytes count
Buffer 1 bytes count
TDES2
Buffer 1 address/Timestamp low
TDES3
Buffer 2 address/Next descriptor address/Timestamp high
TDES0: Transmit descriptor word 0
Bit field
Name
Description
31
OWN
Occupancy bit.
0: Indicates that CPU occupies descriptor.
1: Indicates that DMA occupies descriptor.
DMA clears this bit to 0 after transferring a complete frame or reading out all the data
in buffer. The occupancy bit of first descriptor of the same frame can only be set to 1
after the occupancy bits of the following descriptors are all set to 1.
30:18
Reserved
Reserved, the reset value must be maintained.
17
TTSS
Transmit timestamp status bit.
As a flag bit, when set to 1, it means that the frame timestamp corresponding to the
descriptor is recorded, and the recorded timestamp is placed at TDES2 and TDES3.
This bit is only valid when TDES1.LS is 1.
16
IHE
IP header error.
An IP header error occurs when any of the following occurs:
IPv4 frame:
The value of the header length field is less than 0x5
The value of the header length field does not match the received header length
The value of the header version field does not match the value of the frame