PI7C9X20508GPBNDE Pericom Semiconductor, PI7C9X20508GPBNDE Datasheet - Page 23

• Manufacturer Part Number: PI7C9X20508GPBNDE
• Description: IC PCIE PACKET SWITCH 256BGA
• Manufacturer: Pericom Semiconductor
• Series: GreenPacket™r

Specifications of PI7C9X20508GPBNDE

• Applications: Data Transport
• Interface: Advanced Configuration Power Interface (ACPI)
• Package / Case: 256-PBGA
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -

PI7C9X20508GP
5Port-8Lane PCI Express Switch
TM
GreenPacket
Family
Datasheet
5.8 PORT ARBITRATION
Among multiple ingress ports, the port arbitration built in the egress port determines which incoming packets to be
forwarded to the output port. The arbitration algorithm contains hardware fixed Round Robin, 128-phase Weighted
Round-Robin and programmable 128-phase time-based WRR. The port arbitration is held within the same VC
channel. It means that each port has two port arbitration circuitries for VC0 and VC1 respectively. At the upstream
ports, in addition to the inter-port packets, the intra-port packet such as configurations completion would also join
the arbitration loop to get the service from Virtual Channel 0.
5.9 VC ARBITRATION
After port arbitration, VC arbitration is executed among different VC channels within the same source. Three
arbitration algorithms are provided to choose the appropriate VC: Strict Priority, Round Robin or Weighted Round
Robin.
5.10 FLOW CONTROL
PCI Express employs Credit-Based Flow Control mechanism to make buffer utilization more efficient. The
transaction layer transmitter ensures that it does not transmit a TLP to an opposite receiver unless the receiver has
enough buffer space to accept the TLP. The transaction layer receiver has the responsibility to advertise the free
buffer space to an opposite transmitter to avoid packet stale. In this Switch, each port has its own separate queues
for different traffic types and the credits are sent to data link layer on the fly. The data link layer compares the
current available credits with the monitored ones and reports the updated credit to the counterpart. If no new credit
is acquired, the credit reported is scheduled for every 30 us to prevent the link from entering retrain. On the other
hand, the receiver at each egress port gets the usable credits from the opposite end in a link. The output port
broadcasts them to all the other ingress ports to get packet transmission.
5.11 TRANSATION LAYER TRANSMIT BLOCK (TLP ENCAPSULATION)
The transmit portion of transaction layer performs the following functions. They construct the all types of forwarded
TLP generated from VC arbiter, respond with the completion packets when the local resource (i.e. configuration
register) is accessed, and regenerate the message that terminates at receiver to RC if acting as an upstream port.
Page 23 of 81
June 2009 – Revision 1.5
Pericom Semiconductor