PM7341 datasheet(97/413 Pages) PMC

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PRELIMINARY

INVERSE MULTIPLEXING OVER ATM

PM7341 S/UNI-IMA-84

DATASHEET

PMC-2000223

ISSUE 4

INVERSE MULTIPLEXING OVER ATM

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

which is cleared by the ICP cell processing procedure. Cells received while the

LCD latched status bit is set will be written to the DCB as filler cells, and the write

pointers will be incremented. After an LCD condition is exited, the delay

synchronization of the link must be rechecked and resynchronized. An LCD

defect will cause the IFSM state machine to go into the hunt state to ensure the

delay synchronization is rechecked. The transition of the IFSM into the hunt

state will also cause an OIF anomaly.

10.2.4.6.3

DCB Overrun Status

When cells are written into the DCB, overruns will be checked by comparing the

group read pointer against the link write pointer. If the difference between the

pointers exceeds the maximum allowed DCB depth, then an overrun has been

detected. For IMA, this will cause the overrun latched status-in-link context to be

set.

An overrun condition will not cause the IFSM to exit the sync state.

All user cells will be dropped while the overrun condition persists. The overrun

condition is reset at the reception of an ICP cell with an acceptable delay as long

as the link is clear of LIF or OIF. For TC, an interrupt to the processor will be

generated and normal operation will resume once the overrun condition has

ended.

10.2.4.6.4

DCB Underrun Status

When cells are read from the DCB, underruns will be checked by comparing the

group read pointer against the link write pointer. When an underrun is detected,

all user cells will be dropped until the underrun condition is cleared. The underrun

condition will only be cleared at the reception of an ICP cell, such that the

differential delay may be re-checked. An underrun condition will not cause the

IFSM to exit the sync state.

10.2.4.6.5

Idle Cells on IMA Links

When Idle cells are detected on an IMA link, they will be reported. Idle cells on

IMA links may be present for two reasons. They may have been inserted at the

ATM layer of the transmitter as a rudimentary method for traffic management; in

which case the IMA layer should treat them as user cells. Otherwise, they may

have been inserted at the TC layer to assist with rate matching; this is illegal for

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