ZL30226/GA ZARLINK [Zarlink Semiconductor Inc], ZL30226/GA Datasheet - Page 50

• Manufacturer Part Number: ZL30226/GA
• Description: 4/8/16 Port IMA/TC PHY Device for xDSL
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

sequence is rebuilt, as the read pointer was set using the previous worst case link. If this slower link is to be added,
then the recombiner process has to stop for the time required to receive the cells on the slower link and then the
recombiner process can resume. This causes disruption in the operation of the recombiner and will affect the Cell
Delay Variation (CDV).
To provide an optimal recombiner delay, the ZL30226/7/8 adds a guardband delay to the current worst case
recombination delay when the IMA Group is first started up. Guardband delay is programmable and minimizes the
number of disruptions that would otherwise occur in accommodating link delays exceeding the current worst case.
The guardband delay value is specified for each IMA group by writing to the RX Guardband/Delta Delay
(0x0287-0x028E) registers. It should be the smallest value possible consistent with minimizing the disruptions (the
smallest allowed value is 4). When operational, the value of the guardband delay corresponds to the delay value of
the link having the greater transport delay (the link where the data is the last to arrive to the ZL30226/7/8).
3.3.13.2
The various delays on links of the same IMA Group are measured and compared to the programmed ’maximum
allowable value’ stored in the RX Maximum Operational Delay (0x029A-0x02A1) registers for the IMA Group. This
value corresponds to the worst delay value that is expected. This value cannot be larger than the number of cells
that can be stored in the external memory. The smallest ’maximum allowable value’ is four cells. These values are
independently established for each of the four IMA Groups.
3.3.13.3
If a link to be added is slower and cannot be accommodated by the present guardband, an LODS signal is generated
and the link delay value is reported negative. The value reported is with respect to the read pointer and represents
the minimum number of cells that has to be added to the present guardband before adding the link in the IMA group.
See paragraph 3.3.13.6 Incrementing/Decrementing the Recombiner Delay for more details.
If a link to be added is faster and would cause its write pointer to be set beyond the RX Maximum Operational Delay
(0x029A-0x02A1) programmed value, then the link is reported to be faulty through an LODS condition. The
recombination process will not be affected as long as the amount of delay is not larger than the total number of cells
in the external memory.
LODS will also be reported if, during operation, the delay of a link changes to exhibit higher or lower delay resulting
in a negative delay value or a value beyond the RX Maximum Operating Delay value.
LODS events are reported by the IRQ Link Status (0x0435) register and investigated by selecting the current
maximum delay using the RX Delay Select (0x02AA), RX Delay Register (0x0285) and RX Delay Link Number
(0x0286) register. Link Out of Delay Sychronization (LODS) and end of LODS can optionally generate an interrupt
(IRQ).
3.3.13.4
If the recombiner process is enabled for a link that exhibits a negative delay value, then the recombiner process will
be suspended until the write pointers are moved in such a way that the delay is reported with a positive value of 4.
The recombiner process will then resume and no cells will be lost. The same behavior applies if the delay value of
a link which is part of the round robin process (recombiner bit ON) becomes negative: the recombiner process will
be suspended until the delay value becomes positive with a value of 4. The latter condition can happen under severe
error conditions if the recombiner process of the faulty link is not disabled.
RX Maximum Operational Delay Value
Link Out of Delay Synchronization (LODS)
Negative Delay Values
Zarlink Semiconductor Inc.
ZL30226/7/8
50
Data Sheet