MPC8280 datasheet(1211/1386 Pages) FREESCALE

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Inverse Multiplexing for ATM (IMA)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

34-65

34.5.4.9

Transmit Event Response Procedures

The following TX events may take place when operating in IMA mode. It is recommended that all events

be handled via an “exception/interrupt service routine” (ISR) as the response time inherent with interrupt

driven events should diminish the negative impact/propagation of such events:

1. TQU (Transmit Queue Underrun)—Indicates that a transmit queue was emptied. This implies that

the offending link (PHY) is requesting cells at a faster rate relative to the TRL. If the TRL is out of

spec, then you will see multiple links reporting TQUs (because all links in the group will be faster

relative to the TRL). The offending link should be removed (see Section 34.5.4.5, “Link Removal

Procedure”), check the following: PHY, TX Queue depth (start and end pointers should not be the

same), TNUMLINKS is equal (not less or greater) than the number of active links.

2. TQO (Transmit Queue Overflow)—Indicates that a transmit queue was not ready to receive a cell

(full). This implies that the offending link (PHY) is requesting cells at a slower rate relative to the

TRL. If the TRL is out of spec, then you will see multiple links reporting TQOs (because all links

in the group will be slower relative to the TRL). The offending link should be removed (see

Section 34.5.4.5, “Link Removal Procedure”), check the following: PHY, TX Queue depth (depth

should be the same as other queues), TNUMLINKS is equal (not less or greater) than the number

of active links.

34.5.4.10 Receive Event Response Procedures

The following RX events may take place when operating in IMA mode. It is recommended that all events

be handled via an “exception/interrupt service routine” (ISR) as the response time inherent with interrupt

driven events should diminish the negative impact/propagation of such events:

1. LS (Link Stalled)—The link’s DCB has emptied, either because the PHY is no longer functioning

or it is relatively slower than the other links. The offending link should be removed (see

Section 34.5.4.5, “Link Removal Procedure”). Make sure the DCB start and end pointers are not

the same. If only one link is used in a group the software must monitor the TC layer to detect that

this link has stalled. No LS event is reported in the IMA interrupt queue. To re-start an IMA group

properly after link(s) have recovered, the user must reset all the microcode-managed parameters in

the IMA receive group to zero.

2. DCBO (DCB Overflow)—Indicates that the Delay Compensation Buffer has no more space. The

source of the problem can be varied: 1) the offending PHY is sending at a faster rate (out of spec.),

2) the propagation delay of one of the other links in the group is greater than anticipated (need to

make DCB larger) or, 3) the size of the offending link was programmed incorrectly, i.e., smaller

(the size of all DCBs in the group should be the same). The offending link should be removed (see

Section 34.5.4.5, “Link Removal Procedure”). This exception corresponds to the LODS (Link Out

of Delay Synchronization Defect) and should be reported to the FE (via the ICP cell, RxDefect =

LODS) of the problem. The MPC8280 will continue to report this exception if the condition

persists (unless the event is masked).

3. LDS (Link Delay Synchronized)—Indicates that the new/added link (to an existing group) has

achieved synchronization (link delay). The link is capable of receiving data at this point, (see

Section 34.5.4.4, “Link Addition Procedure”).

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