SMSC LAN9312 - Manual (Page 420)

High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface
Datasheet
Revision 1.4 (08-19-08) 420 SMSC LAN9312
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
(BM_RNDM_DSCRD_TBL_RDATA) can be read following a write to this register.
For a wr ite access, the Buffer Manager Random Discar d Table Write Data Register
(BM_RNDM_DSCRD_TBL_WDATA) 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