MT90220
different options are available and are selected by bit
1 and 0 of the UTOPIA Input Control register.
Status register. These status bits are cleared by
overwriting them with 0. Additionally, for each status
bit there is an Interrupt Enable bit in the associated
RX UTOPIA Link FIFO Overflow Enable or RX
UTOPIA IMA Group FIFO Overflow Enable
register. When enabled, the status bit is reported in
an Interrupt register. See 6.2 Interrupt Block for more
details.
•
The ’00’ option is used to always accept a cell
from the ATM layer. The HEC is verified and if
wrong, the UTOPIA Input counter associated
with the UTOPIA port for cells with bad HEC is
incremented. The MT90220 will re-generate a
valid HEC based on the content of the 4-byte
header that was received.
The size of the RX UTOPIA FIFO is fixed at two cells
for the UNI PHY Addresses and four cells for the IMA
Group PHY Addresses.
•
The ’01’ option is used to verify the HEC of an
incoming cell. If the HEC value is wrong and if it
can be corrected (1 bit error), then the cell is
corrected and accepted as a good cell. The bad
HEC counter is not incremented if the HEC is
corrected. The bad HEC counter is incremented
if the HEC value cannot be corrected. In this
mode, the cell is always accepted. The
MT90220 will re-generate a valid HEC based on
the content of the 4-byte header that was
received.
5.3 UTOPIA Operation With a Single PHY
A single ATM layer device with a UTOPIA L2 MPHY
port can be connected to the ATM input port of one
MT90220. Another ATM-Layer device using the
UTOPIA L2 MPHY input interface is used to receive
ATM cells from the MT90220.
•
•
The ’10’ option is used to verify the HEC on the
incoming cell and discard the cell if the HEC
value is wrong. The bad HEC counter is
incremented if a cell is discarded.
The address pins should be set to the value
programmed by the management interface.
In this mode, the bit 6 and 5 of the Test 1 register are
not to be set to 1 for the proper operation of the RX
Utopia port.
The ’11’ option is similar to mode ’01’ except
that if the HEC value cannot be corrected, then
the cell is discarded. If the HEC value is
corrected, the bad HEC counter is not
incremented.
5.4 UTOPIA Operation with Multiple PHY
When more than one MT90220 are connected to a
single ATM Layer device the single TxClav and
RxClav scheme is used. Direct Status Indication and
Multiplexed Status Polling schemes are not
supported. The necessary polling is performed by
the ATM-Layer device.
5.2 ATM Output Port
The MT90220 supports a 53 byte cell stream via the
ATM output port. Cells received at the ATM output
port are stored in the RX UTOPIA FIFO before being
processed by the UTOPIA Interface. The output of
the UTOPIA Interface can be stopped by the ATM
Layer device by de-asserting the RxEnb* signal.
The UTOPIA Interface transmit and receive
addresses, provided by the ATM-Layer device, are
used to de-multiplex the ATM-cell stream to as many
as eight MT90220s. The maximum available
bandwidth for eight E1 lines served by each
MT90220 device is 2 MBytes/s.
The start of a cell is marked with the SOC signal,
which is active during the transmission of the first
byte of a cell. The following 52 bytes are expected to
belong to the same cell.
The RX byte clock (RxClk) can be up to 25 MHz and
is checked against the system clock. If the incoming
byte clock frequency is lower than 1/128 of the
system clock, bit 3 of the General Status register
will be set. This bit is cleared by overwriting it with
0.The RxClk signal has to be synchronized with the
System Clock for the proper operation of the
MT90220. Typically, both frequencies are equal but
the RxClk frequency can be lower.
5.5 UTOPIA Operation in UNI Mode
In UNI Mode, each Utopia port inside an MT90220
corresponds to a physical T1 or E1 line. Up to eight
PHY ports can be supported by one MT90220. Up to
eight MT90220 can be connected to a UTOPIA bus.
The ports in the same device represent only one
electrical load on the UTOPIA bus. The UTOPIA
Interface supports up to 31 PHY addresses so a
maximum of 31 PHY addresses are supported by the
MT90220.
Overflow conditions in the RX UTOPIA FIFO
associated with any of the 12 PHY RX Addresses
cause a status bit to be set in either the IRQ UTOPIA
UNI Overflow Status or IRQ IMA Group Overflow
The MPHY address at the input port of MT90220
(TxAddr[4:0]) is used to store the cell in one specific
TX UTOPIA FIFO.
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MITEL [ MITEL NETWORKS CORPORATION ]
