MT90221 Zarlink Semiconductor, MT90221 Datasheet - Page 26

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

3.3.1
In IMA mode, the transmitter inserts special ICP cells
in the various outgoing streams every M ATM cells to
comply with the IMA specification. The receive block
is using these ICP cells to synchronize with the Far
End transmit side and to reconstruct the ATM cell
original sequence.
3.3.1.1
The
Synchronization State Machines (IFSM) for each
link, as described in Section 11 of the IMA
Specification. The values of Alpha, Beta and Gamma
are programmable through the Frame Delineation
register. Their values are the same for all links.
After the link is programmed to be in IMA mode by
writing to the RX Link Control register, the IMA
Frame State Machine is enabled. At the same time,
the parameter’s value of the RX link are latched in
internal reference registers and are used to
determine if the received ICP cell meets the valid
IICP
synchronization. Refer to section 3.3.1.2 and 3.3.1.3
for the list of link’s parameters.
RXSYNC
RXSYNC
RXCK
RXCK
DSTi
DSTi
cell
ICP Cell Processor
[0]
[3]
MT90220
IMA Frame Synchronization
criteria
S/P
S/P
implements
to
determine
Delineation
Delineation
Figure 7 - The MT90221 Receiver Circuit in IMA Mode
Cell
Cell
Registers
Link Info
IMA
IMA
Processing
Processing
Micro
ICP
ICP
Frame
With Changes
frame
ICP Cell
Buffer
Machine
Machine
Frame
Frame
State
State
IMA
IMA
Incoming ICP cells are automatically detected by the
ICP Processing block. As soon as one valid ICP cell
is received, the IMA Frame State Machine moves to
the IMA PRESYNC state. When Gamma-valid ICP
cells are received, the state machine moves to the
IMA SYNC state. In the IMA PRESYNC state, one
errored or missing ICP cell causes the state machine
to return to the IMA HUNT state. In the IMA SYNC
state, the state machine is forced to the IMA HUNT
state by any of the following events:
•
•
•
Bits 3 and 2 of the RX State register report the IMA
Frame State Machine state for a selected link. When
in IMA HUNT mode, the information required to
perform the verification is extracted from the ICP
cells received.
After the received information is validated, the IMA
Group is configured by writing to the RX Reference
Link Control, the RX Link Control and RX
Recombiner registers.
one missing ICP cell
Alpha consecutive invalid ICP cells
Beta consecutive errored ICP cells
RAM Area
Controller
Recovery
RAM
Rate
Scheduler
RX
Recovered
Cell CLK
MT90221
UTOPIA
Interface
17