FBFM2112F897CSLJLS View Datasheet(PDF) - Intel

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Description

Manufacturer

FBFM2112F897CSLJLS

Intel® FM2112 24-Port 10G/1G Ethernet Switch Chip

Intel 

Intel® FM2112 24-Port 10G/1G Ethernet Switch Chip Data Sheet

3.3.5

Turning the Pause feature off is accomplished by setting the

watermarks for Pause to a level which is higher than the device can

attain.

Egress Scheduling

{Described in registers Table 108 and Table 109}

Egress scheduling is the rules applied to determine which frames are to

be transmitted next on the port from the Egress Scheduling Priority

Queues (ESPQ). The priority used to determine the scheduling is the

Egress Scheduling Priority, which is defined in section 3.3.1. Egress

scheduling is an independent function on each output port. In the

Intel®Ethernet Switch Family, Egress Scheduling is based on the

number of frames transmitted, not on bytes transmitted or number of

segments transmitted.

There are two scheduling modes,

• Strict Priority - Always schedule the frame of the highest priority queue that is

ready to transmit

• “Priority Weighted Round Robin” - Service the priority queues in round-robin

fashion, scheduling a weighted number of frames per turn per queue. The order in

which frames between queues are scheduled, up to the ESPQs' weights, is

configurable

— In priority order, using credit only as the ESPQ is serviced.

— Pure round robin: schedule the number of frames equal to the weight or until

the queue is empty then proceed to the next queue.

Each priority queue can be in either scheduling mode. That is, some

queues could be strict priority while other queues are WRR. This is

implemented internally with the following constructs:

Eligibility

• An ESPQ is said to be eligible if and only if at least one frame within the queue is

ready to be transmitted.

— In store-n-forward mode this means the whole frame is in the ESPQ.

— In cut-through mode, this means the head sub-segment is in the ESPQ.

Initial Credit

• The initial credit is the weight given to the ESPQ. It is the number of frames the

queue may schedule per turn.

Credit Decrementing

• A strict priority ESPQ never loses credit

• A WRR ESPQ loses credit depending on the service algorithm

— In priority Order (PO), the ESPQ loses one credit per frame transmitted

— In Pure Round Robin (PRR), the ESPQ loses one credit per frame transmitted,

and all remaining credits once it is not eligible.

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