KSZ8863RLL-EVAL Micrel Inc, KSZ8863RLL-EVAL Datasheet - Page 26

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KSZ8863RLL-EVAL

Manufacturer Part Number
KSZ8863RLL-EVAL
Description
BOARD EVALUATION FOR KSZ8863RLL
Manufacturer
Micrel Inc
Datasheet

Specifications of KSZ8863RLL-EVAL

Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Other names
576-3868
Micrel, Inc.
KSZ8863MLL/FLL/RLL
Switching Engine
The KSZ8863MLL/FLL/RLL features a high-performance switching engine to move data to and from the MACs’ packet
buffers. It operates in store and forward mode, while the efficient switching mechanism reduces overall latency.
The switching engine has a 32kB internal frame buffer. This buffer pool is shared between all three ports. There are a total
of 256 buffers available. Each buffer is sized at 128 bytes.
MAC Operation
The KSZ8863MLL/FLL/RLL strictly abides by IEEE 802.3 standards to maximize compatibility.
Inter Packet Gap (IPG)
If a frame is successfully transmitted, the 96 bits time IPG is measured between the two consecutive MTXEN. If the
current packet is experiencing collision, the 96 bits time IPG is measured from MCRS and the next MTXEN.
Back-Off Algorithm
The KSZ8863MLL/FLL/RLL implements the IEEE 802.3 standard for the binary exponential back-off algorithm, and
optional "aggressive mode" back-off. After 16 collisions, the packet is optionally dropped depending on the switch
configuration for register 4 (0x04) bit [3].
Late Collision
If a transmit packet experiences collisions after 512 bit times of the transmission, the packet is dropped.
Illegal Frames
The KSZ8863MLL/FLL/RLL discards frames less than 64 bytes, and can be programmed to accept frames up to1518
bytes, 1536 bytes or 1916 bytes. These maximum frame size settings are programmed in register 4 (0x04). Since the
KSZ8863MLL/FLL/RLL supports VLAN tags, the maximum sizing is adjusted when these tags are present.
Full Duplex Flow Control
The KSZ8863MLL/FLL/RLL supports standard IEEE 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KSZ8863MLL/FLL/RLL receives a pause control frame, the KSZ8863MLL/FLL/RLL will not
transmit the next normal frame until the timer, specified in the pause control frame, expires. If another pause frame is
received before the current timer expires, the timer will be updated with the new value in the second pause frame. During
this period (while it is flow controlled), only flow control packets from the KSZ8863MLL/FLL/RLL are transmitted.
On the transmit side, the KSZ8863MLL/FLL/RLL has intelligent and efficient ways to determine when to invoke flow
control. The flow control is based on availability of the system resources, including available buffers, available transmit
queues and available receive queues.
The KSZ8863MLL/FLL/RLL will flow control a port that has just received a packet if the destination port resource is busy.
The KSZ8863MLL/FLL/RLL issues a flow control frame (XOFF), containing the maximum pause time defined by the IEEE
802.3x standard. Once the resource is freed up, the KSZ8863MLL/FLL/RLL sends out the other flow control frame (XON)
with zero pause time to turn off the flow control (turn on transmission to the port). A hysteresis feature is provided to
prevent the flow control mechanism from being constantly activated and deactivated.
The KSZ8863MLL/FLL/RLL flow controls all ports if the receive queue becomes full.
Half-Duplex Backpressure
A half-duplex backpressure option (not in IEEE 802.3 standards) is also provided. The activation and deactivation
conditions are the same as full duplex flow control. If backpressure is required, the KSZ8863MLL/FLL/RLL sends
preambles to defer the other stations' transmission (carrier sense deference).
To avoid jabber and excessive deference (as defined in the 802.3 standard), after a certain time, the
KSZ8863MLL/FLL/RLL discontinues the carrier sense and then raises it again quickly. This short silent time (no carrier
sense) prevents other stations from sending out packets thus keeping other stations in a carrier sense deferred state. If
the port has packets to send during a backpressure situation, the carrier sense type backpressure is interrupted and those
packets are transmitted instead. If there are no additional packets to send, carrier sense type backpressure is reactivated
again until switch resources free up. If a collision occurs, the binary exponential back-off algorithm is skipped and carrier
sense is generated immediately, thus reducing the chance of further collisions and carrier sense is maintained to prevent
packet reception.
November 2009
26
M9999-110309-1.1

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