MU9C8338A データシートの表示（PDF） - MUSIC Semiconductors

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MU9C8338A

10/100Mb Ethernet Filter Interface

MUSIC Semiconductors 

Functional Description

MU9C8338A 10/100Mb Ethernet Filter Interface

1. The CPU issues an increment STPURG command.

Only the STPURG 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.

If the STPURG value was incremented, the MU9C8338A

initiates a purge operation using the new STPURG value.

STPURG should never be incremented to equal STCURR.

The time stamping of LANCAM entries and the procedure

required to initiate a purge is explained as follows:

1. Incoming SAs to be learned are associated with the

most recent STCURR value. The time stamps of each

SA already in the CAM database is updated to

STCURR, each time a packet with that SA is processed.

2. STPURG and STCURR are advanced as described

earlier to purge entries that have the same time stamp

value as STCURR.

Following is an example, beginning with the defaults,

initially, STCURR = 00H and STPURG = 01H. As

packets arrive, learned or refreshed, SAs are labeled with

STCURR = 00H. (At that moment STPURG = 01H).

Increment, either hardware or software initiated, results in

STCURR = 01H and STPURG=02H.

A purge operation is initiated that will eliminate all CAM

entries with time stamp = 02H. The oldest entries (SAs)

that have not been updated in 255 increment times are

purged automatically without further involvement.

If the CAM Full flag is asserted, an interrupt (if

configured) to the CPU is generated. Assume that

STCURR = F0H, and STPURG = F1H. The CPU may

initiate an increment STPURG operation so that older

entries may be purged. This increases the value of

STPURG to F2H. A purge operation is initiated that will

eliminate all CAM entries with time stamp = F2H.

The CPU should monitor the System Status register, and if

the CAM is still full, the operation can be repeated until

entries are purged and the CAM Full flag is de-asserted.

Assume that STPURG was incremented 128 times. This

would purge the oldest half of the time stamp values and

thus, reduce the maximum age to half the previous 255.

This can be accomplished without disturbing ongoing

normal increment time stamp update operations.

CRC and Other Data Integrity Checks

For 10Base-X packets, a 32-bit cyclic redundancy check is

calculated from the data frame (exclusive of the preamble

and start frame delimiter) and compared to the frame

check sequence (FCS). This check is only performed if the

PCFG register is set accordingly to enable the facility.

Also, according to the MII interface specifications, the

RX_ER, CRS, and COL signals are monitored and error

conditions are recognized. If any error is identified, the

source address is not processed. This is intended to

maintain the integrity of the LANCAM database.

Rev. 0a

11

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