mt90224 Zarlink Semiconductor, mt90224 Datasheet - Page 36

• Manufacturer Part Number: mt90224
• Description: 8-port Ima/tc Phy Device
• Manufacturer: Zarlink Semiconductor

2.4
The MT90222/3/4 supports up to eight independent IMA Groups. Each of the available serial links can be assigned
to any one of these IMA Groups. A serial link cannot be assigned to more than one IMA Group. Refer to Figure 5 for
a functional block diagram of the transmitter.
The IMA transmitter splits the incoming stream into N sub-streams, where 1 ≤ N ≤ (maximum available serial links).
Each sub-stream is passed to a separate line interface device that transmits the cells on a physical link.
The physical line rate is 1.544 Mbps (T1), 2.048 Mbps (E1) or any serial rate up to 2.5 Mb/s (Serial Mode). The
transmitter inserts ICP cells in the various outgoing streams according to the IMA specification. The ICP cells are
inserted every M ATM cells on each link and is the task of the scheduler.
2.4.1
The IMA frame length (value of M) can be 256, 128, 64, or 32. The value of M for each IMA Group is set by the TX
IMA Group FIFO Length Definition (0x0093-0x0096) registers. M is fixed once an IMA Group is setup and should
remain unchanged as long as that group is operational.
2.4.2
The TX ICP Cell Offset (0x0310-0x0317) registers control the position of the ICP cell in the IMA frame for each
link. This parameter should remain unchanged as long as that group is operational.
2.4.3
The MT90222/3/4 supports both the Common Transmit Clock (CTC) and Independent Transmit Clock (ITC) modes
of operation. The desired mode is specified by writing to the TX Group Control Mode (0x0300-0x0307) register. A
reference link must be specified in the TX Group Control Mode (0x0300-0x0307) register. The MT90222/3/4
introduces a Stuff cell on the reference link every 2048 cells and determines the appropriate time to insert a Stuff
cell on the remaining group links. See paragraph 2.4.4, Stuff Cell Rate, for more details.
The clocking mode and reference link are fixed once an IMA Group is set up and should remain unchanged as long
as that group is operational. The reference link should not change unless problems are reported with the link.
2.4.4
The Stuff event algorithm differs between CTC and ITC modes. In CTC mode, the Stuff event is typically fixed and
appears in the same IMA frame on all IMA Group links. In ITC mode, the Stuff event is determined using an
adaptive algorithm that relates the level of the internal TX Link FIFO to that of the TX link FIFO of the Reference
link.
The MT90222/3/4 implements 2 different stuffing algorithms: a fixed stuffing rate and an adaptive stuffing rate. The
Stuffing events do not happen more frequently than once every five IMA frames.
TX Group Control Mode (0x0300-0x0307) register bit 4 selects either the adaptive or fixed algorithm. Bit 5
determines the timing mode declared in the ICP cell.
There are three possible combinations:
•
•
•
CTC Mode with internal Fixed algorithm
CTC Mode with internal Adaptive algorithm
ITC Mode with internal Adaptive algorithm
ATM Transmit Path in IMA Mode
IMA Frame Length (M)
Position of the ICP Cell in the IMA Frame
Transmit Clock Operation
Stuff Cell Rate
Zarlink Semiconductor Inc.
MT90222/3/4
36
Data Sheet