Two Port 10/100 Managed Ethernet Switch with 16-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08)
422
SMSC LAN9311/LAN9311i
DATASHEET
14.5.4.10
Buffer Manager Random Discard Table Command Register (BM_RNDM_DSCRD_TBL_CMD)
This register is used to read and write the Random Discard Weight table. A write to this address
performs the specified access. This table is used to set the packet drop probability verses the buffer
usage.
For a read access, t he
Buff er Manager Random Di scard Tab le Re ad Data Register
can be read following a write to this register.
For a wr ite access, the
Buffer Manager Random Discar d Table Write Data Register
should be written before writing this register.
Register #:
1C09h
Size:
32 bits
BITS
DESCRIPTION
TYPE
DEFAULT
31:5
RESERVED
RO
-
4
Random Discard Weight Table RnW
Specifies a read (1) or a write (0) command.
R/W
0b
3:0
Random Discard Weight Table Index
Specifies the buffer usage range that is accessed.
There are a total of 16 probability entries. Each entry corresponds to a range
of the number of buffers used by the ingress port. The ranges are structured
to give more resolution towards the lower buffer usage end.
R/W
0h
BIT
VALUES
BUFFER USAGE LEVEL
0000
0 to 7
0001
8 to 15
0010
16 to 23
0011
24 to 31
0100
32 to 39
0101
40 to 47
0110
48 to 55
0111
56 to 63
1000
64 to 79
1001
80 to 95
1010
96 to 111
1011
112 to 127
1100
128 to 159
1101
160 to 191
1110
192 to 223
1111
224 to 255