MT90502 Datasheet, PDF (64/191 Pages) Zarlink Semiconductor Inc – Multi-Channel AAL2 SAR

MT90502
Preliminary Datasheet
If the SOC is not set after the 53rd byte of a received cell, subsequent bytes are ignored until a new SOC is
received.
Data received on all three ports is examined for parity errors and an interrupt is raised if an error is found. Cells
are not discarded if a parity error is detected. Register 60Ah indicates on which port the parity error is detected.
The ATM HEC is not examined on received cells.
2.6.5 Cell Routing
Cells are read in a cyclic manner from the 4-cell input FIFOs. Cells from the TX_SAR that contain a '0' in the
MSB of the TXD field (see Figure 21, “TX Cell Format,” on page 43) are written into the output FIFOs
designated by the three LSBs of the TXD field. The TXD field may also indicate that the cell is routed through
one of the 3 look-up tables. Therefore, the cell follows the same path as if it came from one of the 3 UTOPIA
input ports. Cells written into the RX_SAR FIFO can be directed to the SAR portion (cells to be formatted into
TDM streams), to the data cell portion (to be examined by the CPU), or to both. This is indicated by the RXD
field (see Figure 35, “RX Cell Format,” on page 64) in cells written into the RX_SAR output FIFO.
RX Cell Format
(of cells written in each of the internal input cell FIFOs in the UTOPIA interface)
b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
+0
GFC/VPI
VPI
VCI [15:12]
+2
VCI [11:0]
OAM PTI CLP
+4
Payload Byte 0
Payload Byte 1
+6
Payload Byte 2
Payload Byte 3
+30
+32
+34 Port #
+36
+38
+3A
+3C
+3E
Payload Byte 44
Payload Byte 46
Payload Byte 45
Payload Byte 47
VC Number
RXD
Reserved
RX SAR Output FIFO structure is 64-bytes in size, located in internal memory at addresses 3000h to 3FFEh.
Port #:
VC Number:
RXD:
“00” = comes from LUT A, “01” = comes from LUT B, “10” = comes from LUT C; others = reserved
indicates the VC to which this cell is destined, if it is destined to the RX SAR.
RX Destination. “1x” = Destined to RX SAR, “x1” = destined to AAL0 FIFO.
2.6.5.1 Mask & Match Process
Figure 35 - RX Cell Format
Cells received on the UTOPIA port are designated as “known” or “unknown” based on the result of a mask &
match process (configured for each port). For a cell to be considered “known”, all VPI/VCI bits whose
corresponding mask bit is '1' must have the value contained in the corresponding bit of the match register. In
addition, the MT90502 can be configured to eliminate null cells (those with VPI = 0 and VCI = 0). For the
purpose of null cell elimination, the NNI/UNI can be included on a per-port basis (Register 60Eh).
Unknown cells can be discarded or directed to one or more output FIFOs. All unknown non-OAM cells from a
port are discarded or directed to the same location(s) and all unknown OAM cells from a port are discarded or
directed to the same location(s). Unknown cells can be directed differently for each port on which they were
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