MT90221 Zarlink Semiconductor, MT90221 Datasheet - Page 31

• Manufacturer Part Number: MT90221
• Description: Quad Inverse Multiplexing For Atm (IMA) Device With Flexible Ima And Uni Mode
• Manufacturer: Zarlink Semiconductor

MT90221
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
MT90220/221 Programmer’s Manual and example
code).
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3.3.12 Link Addition
The MT90221 supports software controlled link
addition to the existing RX link group. Such an
addition
bandwidth. The added link receives Filler cells until
the Far End (FE) TX side is active. During this time,
the new link’s delay is measured and compared with
the current operating limits. The link is either rejected
or accepted. The operational delay can be corrected
if required as described in 3.3.10.6 Incrementing/
Decrementing
synchronization is achieved, the added link can be
included in the recombiner algorithm using bit 2 of
the RX Recombiner register. The link will be
effectively included in the IMA Group when the
corresponding bit in the Enable Recombination
Status register is set.
A link may also be added to an IMA Group when the
first User cell is received. This is done by writing to
the RX Recombiner Delay Control register.
3.3.13 Link Deletion
There are two reasons to deactivate a link:
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Configure the SRAM parameters using the
SRAM Control, RX External SRAM Control
and Test Mode Enable registers
Configure the Cell delineation and IMA Frame
State Machines parameters by writing to the
Cell Delineation, Loss Cell Delineation and
IMA Frame Delineation registers
Write to the RX Link Control register to select
the RX options
Configure the RX PCM port(s) by writing to the
RX PCM Link Control register
Configure the RX UTOPIA port by writing to the
UTOPIA Output Group PHY Enable and
UTOPIA OutputGroup Address registers
Validate the IMA parameter values received
over the PCM links and configure the link in IMA
mode using the RX Recombiner and the RX
Link Control register
When ready, start the recombiner process by
writing to the RX Recombiner register
the bandwidth required decreases or
can
be
the
used
Recombiner
to
increase
Delay.
available
After
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Both link deactivation procedures specified in the
IMA specification are supported under the control of
software.
The command to disable the recombination process
for a link is issued by writing to bit 2 of the RX
Recombiner register.
If the delay of the link to be removed is not the worst
delay, then no pointer correction is required and the
recombiner bit (i.e., bit 2 of RX Recombiner register)
for the removed link should be set to 0.
If it is the worst case delay, then the pointer values
should be corrected to reduce the amount of
additional delay introduced by the recombiner. The
pointers need to be changed (advanced). This
results in reducing the number of cells (the amount
of time) required for the recombiner process.
To reduce the impact of this correction, its
implementation can either be immediate or delayed.
A command in the Increment/Decrement Delay
Control register is used for this purpose (refer to
3.3.10.6
Recombiner Delay, for more details).
3.3.14 Disabling an IMA Group
Before an IMA Group can be disabled, the software
should ensure that no User cells are left in memory.
As part of the higher level handshaking, the TX FE
should have sent Filler cells for a while for the RX
side to process all the User cells that could be in the
external memory.
The procedure to follow is to stop the recombination
process and then, wait for the enable process to be
reported inactive (in the Enable Recombination
Status register) before re-assigning the link to
another IMA group or to UNI Mode.
3.4
Up to four incoming T1/E1 lines can be connected to
the MT90221 receiver and forwarded to the UTOPIA
L2 interface served by an external ATM-Layer device
in UNI Mode. Figure 8 illustrates four of the eight
possible UTOPIA ports that can be addressed
through the UTOPIA Interface.
The size of the RX UTOPIA FIFO is fixed. The Idle
cells are automatically removed at the RX PCM block
and all other valid received cells are transferred to
the RX UTOPIA FIFO.
an existing link becomes faulty.
The ATM Receive Path in UNI
Incrementing/Decrementing
the