MT90220
RAM Area
IMA
RXCK
RXSYNC
DSTi
Cell
Delineation
ICP
Processing
Frame
S/P
UTOPIA
Interface
State
Machine
[0]
RAM
Controller
RX
Scheduler
IMA
RXCK
RXSYNC
DSTi
Recovered
Cell CLK
Cell
Delineation
ICP
Processing
Frame
S/P
State
Machine
[7]
ICP Cell
With Changes
Buffer
Link Info
Registers
Rate
Recovery
Micro
Figure 7 - The MT90220 Receiver Circuit in IMA Mode
3.3.1 ICP Cell Processor
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:
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 IMA Frame Synchronization
The
MT90220
implements
IMA
Frame
•
•
•
one missing ICP cell
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.
Alpha consecutive invalid ICP cells
Beta consecutive errored ICP cells
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 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
ICP cell criteria to determine IMA frame
synchronization. Refer to section 3.3.1.2 and 3.3.1.3
for the list of link’s parameters.
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.
17
MITEL [ MITEL NETWORKS CORPORATION ]
