LAN9312 datasheet(421/458 Pages) SMSC

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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

SMSC LAN9312

421

Revision 1.2 (04-08-08)

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.

1C09h

Size:

32 bits

BITS

DESCRIPTION

TYPE

DEFAULT

31:5

RESERVED

Random Discard Weight Table RnW

Specifies a read (1) or a write (0) command.

R/W

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

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

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