VSC7440 datasheet(314/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

297

Figure 96 •

PFC Generation Per Port

3.33.1.3 Statistics

The number of transmitted pause frames is counted in the TX_PAUSE_CNT counter and shared with the

counter for transmitted link-layer flow control pause frames. Statistics are handled locally in the DEV10G

port modules. For other port module types, the assembler handles the statistics.

3.33.2

PFC Frame Reception

Received PFC frames are detected by the assembler. The status is forwarded to the queue system,

which will pause the egress traffic according to the timer value specified in the pause frames.

3.33.2.1 Assembler

The assembler identifies PFC PDUs and stores the received pause time values in a set of counters. The

counters are decremented according to the link speed of the port. The assembler signals a stop

indication to the queue system for all (port, priority) with pause times different from 0.

For information about the PFC configuration of the assembler, see Setting Up PFC, page 53.

3.33.2.2 Queue System

The queue system stores the PFC stop indications received from the assembler per (port, priority). It

pauses the transmission for all egress queues with an active PFC stop indication. The queue system

does not require any PFC configuration.

3.33.2.3 Statistics

PFC pause frames are recognized as control frames and counted in the RX_UNSUP_OPCODE_CNT

counter. Statistics are handled locally in the DEV10G port modules. For other port module types, the

assembler handles the statistics.

3.34

Protection Switching

The following types of hardware-assisted protection switching are supported:

FC Inactive

Transmit PFC PDU

fc_txed = fc_qs

timer = TX_PAUSE_VAL

PFC Sent

fc_qs unchanged

PFC Sent

fc_qs changed

Transmit PFC PDU

(xoff)

timer =

PFC_MIN_UPDATE_TIME

fc_qs == 0x00

timer < (TX_PAUSE_VAL –

PFC_MIN_UPDATE_TIME)

fc_qs != 0x00

(timer == 0 || !PFC_XOFF_MIN_UPDATE_ENA)

fc_qs != fc_txed

fc_qs == fc_txed

timer < TX_PAUSE_VAL/2

fc_qs != 0x00

timer < (TX_PAUSE_VAL –

PFC_MIN_UPDATE_TIME)

fc_qs: Congestion state per priority from QS

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