KSZ9567R datasheet(28/233 Pages) MICROCHIP

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KSZ9567R

DS00002329E-page 28

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To ensure no packet loss in 10BASE-Te or 100BASE-TX half-duplex modes, the user must enable the following:

• No excessive collision drop (Switch MAC Control 1 Register)

• Back pressure (Port MAC Control 1 Register)

4.3.8

FLOW CONTROL AND BACK PRESSURE REGISTERS

Table 4-4 provides a list of flow control and back pressure related registers.

4.3.9

BROADCAST STORM PROTECTION

The device has an intelligent option to protect the switch system from receiving too many broadcast packets. As the

broadcast packets are forwarded to all ports except the source port, an excessive number of switch resources (band-

width and available space in transmit queues) may be utilized. The device has the option to include “multicast packets”

for storm control. The broadcast storm rate parameters are programmed globally, and can be enabled or disabled on a

per port basis. The rate is based on a 5ms interval for 1000BASE-T, a 50ms interval for 100BASE-TX and a 500ms

interval for 10BASE-Te. At the beginning of each interval, the counter is cleared to zero and the rate limit mechanism

starts to count the number of bytes during the interval. The rate definition is described in control registers. The default

setting equates to a rate of 1%.

4.3.10

SELF-ADDRESS FILTERING

Received packets can be filtered (dropped) if their source address matches the device's MAC address. This feature is

useful for automatically terminating packets once they have traversed a ring network and returned to their source. It can

be enabled on a per-port basis via the Switch Lookup Engine Control 1 Register and Port Control 2 Register.

4.4

Switch

4.4.1

SWITCHING ENGINE

A high-performance switching engine is used to move data to and from the MAC's packet buffers. It operates in store

and forward mode, while an efficient switching mechanism reduces overall latency. The switching engine has a

256KByte internal frame buffer that is shared between all the ports.

For the majority of switch functions, all of the data ports are treated equally. However, a few functions such as IGMP

snooping, 802.1X, forwarding invalid VLAN packets, etc., give special recognition to the host port. Any port (but most

commonly port 6 or port 7) may be assigned as the host port by enabling tail tagging mode for that port. Only one port

may be a host port.

TABLE 4-4:

FLOW CONTROL AND BACK PRESSURE REGISTERS

Registers

Description

LED Configuration Strap Register

LED configuration strap settings.

(LED1_1 enables flow control and back pressure)

Switch MAC Address 0 Register

through

Switch MAC Address 5 Register

Switch's MAC address, used as source address of PAUSE control

frames

Switch MAC Control 0 Register

“Aggressive back-off” enable

Switch MAC Control 1 Register

BP mode, “Fair mode” enable, “no excessive collision drop” enable

Switch MAC Control 4 Register

Pass PAUSE control frames

Port Status Register

Flow control enable (per port)

PHY Auto-Negotiation Advertisement Register PHY - flow control advertisement (per port)

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