KSZ8864RMNI MICREL [Micrel Semiconductor], KSZ8864RMNI Datasheet - Page 32

• Manufacturer Part Number: KSZ8864RMNI
• Description: Integrated 4-Port 10/100 Managed Switch with Two MACs MII or RMII Interfaces
• Manufacturer: MICREL [Micrel Semiconductor]

September 2011
The KSZ8864RMN will not forward the following packets:
1. Error Packets.
2. IEEE802.3x PAUSE Frames.
3. "Local" Packets.
Half-Duplex Back Pressure
The KSZ8864RMN also provides a half-duplex back pressure option (note: this is not listed in IEEE 802.3 standards).
The activation and deactivation conditions are the same as the ones given for full-duplex mode. If back pressure is
required, the KSZ8864RMN sends preambles to defer the other station's transmission (carrier sense deference). To
avoid jabber and excessive deference as defined in IEEE 802.3 standard, after a certain period of time, the
KSZ8864RMN discontinues carrier sense but raises it quickly after it drops packets to inhibit other transmissions.
This short silent time (no carrier sense) is to prevent other stations from sending out packets and keeps other
stations in a carrier sense deferred state. If the port has packets to send during a back pressure situation, the carrier-
sense-type back pressure is interrupted and those packets are transmitted instead. If there are no more packets to
send, carrier-sense-type back pressure becomes active again until switch resources are free. If a collision occurs, the
binary exponential backoff algorithm is skipped and carrier sense is generated immediately, reducing the chance of
further colliding and maintaining carrier sense to prevent reception of packets.To ensure no packet loss in 10BASE-T
or 100BASE-TX half-duplex modes, the user must enable the following:



These bits are not set as the default because this is not the IEEE standard.
Broadcast Storm Protection
The KSZ8864RMN has an intelligent option to protect the switch system from receiving too many broadcast packets.
Broadcast packets are normally forwarded to all ports except the source port and thus use too many switch
resources (bandwidth and available space in transmit queues). The KSZ8864RMN 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 50ms interval for 100BT and a 500ms interval for
10BT. At the beginning of each interval, the counter is cleared to zeroand the rate limit mechanism starts to count the
number of bytes during the interval. The rate definition is described in Registers 6 and 7. The default setting for
Registers 6 and 7 is 0 x 4 A (74 decimal). This is equal to a rate of 1%, calculated as follows: 148,800 frames/sec ¥
50ms/interval ¥ 1% = 74 frames/interval (approx.) = 0x4A.
MII Interface Operation
The media independent interface (MII) is specified by the IEEE 802.3 committee and provides a common interface
between physical layer and MAC layer devices. The KSZ8864RMN provides two MAC layer interfaces for MAC 3
and MAC 4. Each of these MII/RMII interfaces contains two distinct groups of signals, one for transmission and the
other for receiving.
These include framing errors, Frame Check Sequence (FCS) errors, alignment errors, and illegal size packet
errors.
KSZ8864RMN intercepts these packets and performs full duplex flow control accordingly.
Based on destination address (DA) lookup, if the destination port from the lookup table matches the port from
which the packet originated, the packet is defined as "local."
Aggressive backoff (Register 3, bit 0)
No excessive collision drop (Register 4, bit 3)
Back pressure (Register 4, bit 5)
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M9999-092011-1.4