MT90220
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 3.3.10.6
Incrementing/Decrementing the Recombiner Delay
for more details.
The Maximum Delay over time value can be reset at
any time by writing a clear command to bit 5 in the RX
Delay Select register. The differential delays can be
easily obtained by subtracting the delay values of the
links.
3.3.10.6 Incrementing/Decrementing the
Recombiner Delay
If a link to be added is faster and would cause its
write pointer to be set beyond the RX Maximum
operational Delay 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.
If a link to be added has a delay value which falls
beyond the worst current delay value, then there are
2 options: either reject the link or re-adjust the
pointers. To readjust the pointers, the number of cells
to be added (delta) is specified and corresponds to
the amount of extra delay to be added to the current
recombination delay. The additional delay is first
programmed in the Guardband/Delta Delay register
and then a command to increase the delay is issued
(using the Increment/Decrement Delay Control
register). The MT90220 device stops the recombiner
process for the amount of time specified and then
resumes the recombiner process. No cells are lost
but there is an effect on the CDV. The increment
process is completed when the control bit in the
Increment/Decrement Delay Control register is
returned to a 0 value.
LODS will also be reported if, during operation, the
delay of a link is changing to exhibits higher or lower
delay which result in a negative delay value or
beyond the RX Maximum Operating Delay value.
LODS events are reported by the IRQ Link Status
register and the selected Current Maximum Delay
register for an IMA Group.
3.3.10.4 Negative Delay Values
If the recombiner process is enabled for a link that is
If the link exhibiting the longest transmission delay is
removed, the recombiner delay can be reduced
accordingly. When such a correction occurs, the
number of cells corresponding to the delay correction
will be lost. To reduce the impact of this correction,
its implementation can either be immediate or
delayed. The Increment/Decrement Delay Control
register is used for this purpose. The amount of
delay to be removed (i.e., number of cells) in the
recombiner process is controlled by the Guardband/
Delta Delay register. Alternatively, the links can all
be placed in blocking mode for the transition period
to avoid losing any cells.
exhibiting
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. At this time, the
recombiner process will resume. No cells are lost.
The same behavior applies if the delay value of a link
which is part of the round robin process (recombiner
bit ON) goes 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.
3.3.10.5 Measured Delay Between Links
If a decrement delay command is issued which
would result in a negative delay value on one or
more links, the following action will take place: the
read pointer is re-adjusted as required by the
decrease delay command and since the delay is
negative, the recombiner process is suspended until
the delay on all the link are at least reaching a
positive value of 4. Then, the recombiner process will
resume.
The values and delay type for a selected link(s) or
IMA Group can be read using the RX Delay Select
register.
IMA Group delay types include: the Maximum Delay
over time; the Current Maximum Delay and the
Current Minimum Delay of an IMA Group. Current
Link Delay reports the Current Delay of a link.
These values are all reported through a common RX
Delay register. The value is in number of cells. All
the delay values include the guardband delay value.
The RX Delay Link Number register is reporting the
link number associated with the delay value that is
currently in the RX Delay registers, with the
exception for the Maximum Delay over time value,
where the link number reported is not valid (reports
value of 0).
3.3.11 RX IMA Group Start-Up
A quick initialization sequence for the RX IMA Group
could be as follows (default values can be used for
some registers).
(Note: The startup procedure below is given
indicating the most important steps. A more detailed
and complete sequence can be found in the
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