KSZ8893FQL datasheet(39/109 Pages) MICROCHIP

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KSZ8893FQL

DS00003038A-page 38

 2019 Microchip Technology Inc.

Tag Insertion is enabled by bit [2] of the port registers control 0 and the register 194 to select which source port (ingress

port) PVID can be inserted on the egress port for ports 1, 2, and 3, respectively. At the egress port, untagged packets

are tagged with the ingress port’s default tag. The default tags are programmed in register sets {19,20}, {35,36}, and

{51,52} for ports 1, 2, and 3, respectively, and the source port VID has to be inserted at selected egress ports by bit[5:0]

of register 194. The KSZ8893FQL will not add tags to already tagged packets.

Tag Removal is enabled by bit [1] of registers 16, 32, and 48 for ports 1, 2, and 3, respectively. At the egress port, tagged

packets will have their 802.1Q VLAN Tags removed. The KSZ8893FQL will not modify untagged packets.

The CRC is recalculated for both tag insertion and tag removal.

802.1p Priority Field Re-mapping is a QoS feature that allows the KSZ8893FQL to set the “User Priority Ceiling” at any

ingress port. If the ingress packet’s priority field has a higher priority value than the default tag’s priority field of the

ingress port, the packet’s priority field is replaced with the default tag’s priority field. The “User Priority Ceiling” is enabled

by bit [3] of registers 17, 33, and 49 for ports 1, 2, and 3, respectively.

3.4.10

DIFFSERV-BASED PRIORITY

DiffServ-based priority uses the ToS registers (registers 96 to 111) in the Advanced Control Registers section. The ToS

priority control registers implement a fully decoded, 64-bit Differentiated Services Code Point (DSCP) register to deter-

mine packet priority from the 6-bit ToS field in the IP header. When the most significant 6 bits of the ToS field are fully

decoded, the resultant of the 64 possibilities is compared with the corresponding bits in the DSCP register to determine

priority.

3.4.11

RATE LIMITING SUPPORT

The KSZ8893FQL supports hardware rate limiting from 64 kbps to 88 Mbps, independently on the “receive side” and on

the “transmit side” on a per port basis. For 10BASE-T, a rate setting above 10 Mbps means the rate is not limited. On

the receive side, the data receive rate for each priority at each port can be limited by setting up Ingress Rate Control

Registers. On the transmit side, the data transmit rate for each priority queue at each port can be limited by setting up

Egress Rate Control Registers. The size of each frame has options to include minimum IFG (Inter Frame Gap) or Pre-

amble byte, in addition to the data field (from packet DA to FCS).

For ingress rate limiting, KSZ8893FQL provides options to selectively choose frames from all types, multicast, broad-

cast, and flooded unicast frames. The KSZ8893FQL counts the data rate from those selected type of frames. Packets

are dropped at the ingress port when the data rate exceeds the specified rate limit.

For egress rate limiting, the Leaky Bucket algorithm is applied to each output priority queue for shaping output traffic.

Inter frame gap is stretched on a per frame base to generate smooth, non-burst egress traffic. The throughput of each

output priority queue is limited by the egress rate specified.

If any egress queue receives more traffic than the specified egress rate throughput, packets may be accumulated in the

output queue and packet memory. After the memory of the queue or the port is used up, packet dropping or flow control

will be triggered. As a result of congestion, the actual egress rate may be dominated by flow control/dropping at the

ingress end, and may be therefore, slightly less than the specified egress rate.

To reduce congestion, it is a good practice to make sure the egress bandwidth exceeds the ingress bandwidth.

3.5

Unicast MAC Address Filtering

The unicast MAC address filtering function works in conjunction with the static MAC address table. First, the static MAC

address table is used to assign a dedicated MAC address to a specific port. If a unicast MAC address is not recorded

in the static table, it is also not learned in the dynamic MAC table. The KSZ8893FQL is then configured with the option

to either filter or forward unicast packets for an unknown MAC address. This option is enabled and configured in register

14.

This function is useful in preventing the broadcast of unicast packets that could degrade the quality of the port in appli-

cations such as voice over Internet Protocol (VoIP).

3.6

Configuration Interface

The KSZ8893FQL can operate as both a managed switch and an unmanaged switch.

In unmanaged mode, the KSZ8893FQL is typically programmed using an EEPROM. If no EEPROM is present, the

KSZ8893FQL is configured using its default register settings. Some default settings are configured via strap-in pin

options. The strap-in pins are indicated in Table 2-1.

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