MU9C8338A 查看數據表（PDF） - MUSIC Semiconductors

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MU9C8338A

10/100Mb Ethernet Filter Interface

MUSIC Semiconductors 

MU9C8338A 10/100Mb Ethernet Filter Interface

Functional Description

LANCAM Sequencer

The sequencer is a state machine that generates the control

signals required for CAM read and write cycles, and

multiplexes appropriate data and operational codes to

LANCAM data lines. The sequencer operations are:

• Execute LANCAM cycles for CPU port

• DA processing

• SA processing

• Purging of aged entries

• Add Permanent Entries to LANCAM database

• Delete Entries from LANCAM database

• Read Entries from the LANCAM database.

FIFO and Result Port

When the DA sequence is executed, the result is stored in

a FIFO for later collection by either the CPU over the

Processor Bus from the Result register, or by external

hardware attached to the Result port.

Initialization

At power-up or after a hardware reset, the host processor

should download the LANCAM configuration and register

contents to enable the LANCAM to operate as required.

The LANCAM initialization and configuration that is

downloaded by the CPU should do the following: The

individual Page Address registers of each LANCAM in

the LANCAM chain should be set with appropriate values.

The Foreground Register set should be set to allow normal

DA and SA filtering. This involves setting the Control,

Segment Control, and Mask registers to suit. The

Background Register set should be set to allow the

background management tasks to be preformed. This

involves setting the Control, Segment Control, and Mask

registers to suit. The LANCAM should be configured to

store 48-bit MAC addresses in segments 3–1 and the

associated data in segment 0. The allocation of bits in the

16-bit associated data segment is specified in the

description of the SCDW0 Association Data register.

Permanent Station Addresses

Using the Add Entry routine, the nonvolatile station list

can be added to the LANCAM by the host processor. The

Associated Data bit 15 is set to 1, to indicate a permanent

entry. Permanent entries are removed only with the Delete

Entry routine.

Management

The Delete Entry and Read Entry routines are available for

database maintenance and housekeeping. Although

permanent addresses cannot be purged, they can be deleted

using the management Delete Entry routine.

Aging and Purging

Time stamps are added automatically to the LANCAM

entries by the MU9C8338A. Two counters are provided to

store the current and purge time stamps. The Current Time

Stamp is the 8-bit value that automatically is added or

updated when a SA processing function is completed. The

Purge Time stamp is the 8-bit value that is compared with

the 8-bit time stamps stored with the LANCAM entries

during purges. The initial value of the counters are

STPURG = 01H and STCURR = 00H. The counters may

be incremented individually through the CPU commands.

Either the CPU or the external INCR pin can increment

both counters simultaneously. Whenever STPURG is

incremented, a purge operation is initiated. The counters

roll-over so the times should be thought of as slots to be

used and reused in a round-robin fashion.

The existence of two counters (time stamps) allows the

data-aging rate to be varied according to network traffic

density. When the difference between the counters is large

(default), the address data is purged less frequently;

shrinking the counter difference causes the data to age

sooner. Incoming SAs are time stamped or updated with

the current value of STCURR. Older entries time stamped

with the same value as STPURG are purged upon the

increment of STPURG. The permanent address database

built using the Add routine is not affected by time stamps.

The data age gap is effectively the length of time an entry

will exist in the LANCAM database if it is not updated.

This gap is the difference between the STCURR and

STPURG counter. When network traffic is low, STCURR

may be increased in order to increase the length of time an

entry will exist. When network traffic is high, STPURG

may be increased in order to decrease the length of time an

entry will exist. When STPURG is incremented older

entries are also purged from the database if their time

stamp matches STPURG.

STCURR and STPURG may be incremented

simultaneously to keep the data age gap constant and to

purge the older entries from the database.

To maintain "current" time, STCURR is advanced in any

one of the three ways:

1. The CPU issues an increment STCURR command.

Only the STCURR counter is increased.

2. The CPU issues an increment STCURR and STPURG

command. Both counters are increased simultaneously.

3. The INCR pin is asserted. Both counters are increased

simultaneously.

To maintain "purge" time and to purge aged CAM entries,

STPURG is advanced in any one of the following three

ways:

10

Rev. 0a

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