VT6508 datasheet(21/48 Pages) ETC1

21 / 48 page

VIA Technologies, Inc.

Preliminary VT6508 Datasheet

-21-

*if chip_internal_reg for link status is “down”=> generate link_change

interrupt and disable io_port

Step8. Read PHY ANAR(Reg4) and ANLPAR(Reg5)

- if speed_arbit_bit =”0”(speed from PHY proprietary reg), then go to step9

- if speed_arbit_bit =”1”(speed from ANLPAR), then go to step10

* generate link_change interrupt and enable io_port

Step9. Read PHY proprietary Reg for RMII speed, then go to step10

* generate link_change interrupt and enable io_port

Step10. Done

- if auto-polling_command = “off”, then go to step1, and stay idle

- else go to step2, for next port.

Duplex mode decision rule:

RMII_DUPLEX_MODE = ~( ( ANAR.8 = 1 and ANLPAR.8 =1:100BASE-TX Full )

or ( ( ANAR.7 =0 or ANLPAR.7 =0) and ANAR.6 =1 and ANLPAR.6=1))

Note that value 1 denotes half duplex, 0 denotes full duplex.

Speed decision rule:

According to ANLPAR,

- if ~((ANLPAR.9=1 or ANLPAR.8=1 or ANLPAR.7=1)

then speed = 10MHz

2.4 FLOW CONTROL

In VT6508, there are three policies of resource management for different objectives:

(1) flow control for full-duplex ports

Objective: slow down the input traffic without incurring any drops.

(2) backpressure for half-duplex ports

Objective: slow down the input traffic with intended collision and the Ethernet backoff

mechanism.

(3) drop control for private buffer reservation

Objective: shape the input traffic to be compliant to the buffer reservation discipline.

In the following, we call “congestion control” as aggregation of the above three policies.

The application conditions of resource management policies are as follows:

(1) flow control for full-duplex ports

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