734
/
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
timestamp function is enabled, RDES2 and RDES3 are also used to store the lower 32 bits of the timestamp and the
upper 32 bits of timestamp, respectively (MAC controller will complete the reception of the timestamped frame and
before DMA closes descriptor (RDES0.OWN is cleared to 0), and the timestamp is written to RDES2 and RDES3).
Each bit is defined and described in detail as follows:
:
Table 25-9 Receive 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
RDES0
OWN
AFM
Status bits
RDES1
DIC
Control bits
Buffer 2 bytes count
Buffer 1 bytes count
RDES2
Buffer 1 address/Timestamp low
RDES3
Buffer 2 address/Next descriptor address/Timestamp high
RDES0: Receive 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 filling the buffer
corresponding to descriptor.
30
AFM
Failed destination address filter.
0: The received frame passes destination address filter.
1: The received frame does not pass destination address filter.
29:16
FL[13:0]
Frame length.
These bits indicate the byte length of the received frame transferred to the input
buffer. This bit is only valid when RESD0.LS is 1 and RDES0.DE is 0. If both
RESD0.LS and RESD0.ES are 0, these bits indicate the cumulative number of
bytes that the current received frame has transferred to the memory.
15
ES
Error summary.
This bit is only valid when RESD0.LS is 1.
This bit is the logical OR of:
RDES0[14]: Descriptor error
RDES0[11]: Overflow error
RDES0[7]: IP header error
RDES0[6]: Late collision