mt90503 Zarlink Semiconductor, mt90503 Datasheet - Page 82

• Manufacturer Part Number: mt90503
• Description: 2048vc Aal1 Sar
• Manufacturer: Zarlink Semiconductor

4.5.5
Cells are read on a round-robin basis from the four input FIFOs. Cells from the TX_SAR that contain a ’0’ in the
MSB of the TXD field (see Figure 36 on page 82) are written into the output FIFOs designated by the three LSBs of
the TXD field. Cells from the TX_SAR that contain a ’1’ in the MSB of the TXD field and cells from the RXA, RXB,
and RXC ports are handled based on the VPI/VCI of the cell. The TXD field for a cell is the same as the TXD field in
the TX_SAR control structure that created the cell (see Figure 29 on page 65).
Cells written into the RX_SAR output 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 in cells
written into the RX_SAR output FIFO.
+3Ch
+3Eh
+3Ah
+30h
+32h
+34h
+36h
+38h
+0h
+2h
+4h
+6h
Cell Router
GFC: Generic Flow Control
VPI: Virtual Path Identifier
VCI: Virtual Circuit Identifier
OAM: Management Cell. When this bit is set, the cell does
not contain TDM bytes and is handled as an OAM cell.
PTI: Payload Type Indicator.
CLP: Cell Loss Priority (this bit is not examined by the
MT90503).
Payload Byte X: Payload byte in ATM cell (48 bytes total,
numbered 0 to 47).
TXD: TX_SAR Destination Field.
b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5
Figure 36 - Cell Format for cells in internal UTOPIA input and output cell FIFOs
GFC
GFC
TXD
Payload Byte 46
Payload Byte 44
"0000" = discard cell
"0xx1" = Send to TXA port
"0x1x" = Send to TXB port
"01xx" = Send to TXC port
"1001" = Treat as cell from RXA port
"1010" = Treat as cell from RXB port
"1100" = Treat as cell from RXC port
others = reserved
Payload Byte 0
Payload Byte 2
VCI[11:0]
RX Structure Pointer
VPI
Payload Byte 3
Payload Byte 1
Payload Byte 47
Zarlink Semiconductor Inc.
Payload Byte 45
MT90503
b4 b3
VCI[15:12]
82
b2 b1
PTI
RXD
RXD: RX_SAR destination field.
RX Structure Pointer: Pointer to the RX_SAR Structure
that will be used to process the current cell.
Concatenated with "00000" to form a wp-bit address.
(see RX_SAR structure).
Note that RXA, RXB, and RXC input FIFOs do not
contain any field beyond Payload Byte 47. Also note that
the TX_SAR input FIFO does not contain any field
beyond TXD. The TXD field is not written in any of the
output FIFOs
Note: The HEC field of the ATM cell is calculated and
added for outgoing cells after the cell leaves the FIFO.
b0
"00" = reserved
"x1" = Data Cell (write in RX Data Cell FIFO in
external control memory)
"1x" = RX_SAR CBR Cell (disassemble this
cell with structure pointed to by RX Structure
Pointer (Normal) field)
OAM
CLP
Reserved
Data Sheet