RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
significant bits of the VCI or shifted up 4 bits to occupy bits 12 down to 4 of the
VCI field.
There are two methods of detecting a cell to be redirected to the OAM queue.
The first method uses a data indicator bit in the header. The second method
uses the customary PTI field. If the data indicator is not set (VCI(8) = 0 when
SHIFT_VCI=0) or Payload Type Indicator (PTI) = 4 to 7, the cells are sent to the
OAM queue and are stored using the pointers located in the OAM receive queue
table. The head pointer is the address to the first cell received for each queue,
and is usually maintained by the microprocessor. The tail pointer is the address
of the last cell of the queue, and is maintained by the RALP. The RALP updates
the tail pointer upon each OAM cell arrival.
If the cell is a data cell ( cells received with VCI(8) = 1 when SHIFT_VCI=0 and
PTI = 0 to 3), the cell is sent to the queue with VCI(7:0). Bits 7:5 determine the
line, and bits 4:0 determine the queue. The A1SP block ignores VCI(15:9) and
VPI(11:0). If SHIFT_VCI = 1, the interpretation of the VCI bits is shifted by four
bits.
There is also a special mode when VP_MODE_EN is set in the UI_COMN_CFG
register. When set the VPI field is used to select the Line number. Queue 0 is
always assumed. So this mode is only available if all lines are configured with
one queue. Normally this mode can only be used if all lines are configured in
UDF-ML mode. In this mode the VCI field is used to detect an OAM cell. If the
VCI is less than or equal to 31 then the cell will go to the OAM cell buffer.
Figure 33 shows the interpretation of the incoming cell header once the cell
arrives at the A1SP.
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
103
PMC [ PMC-SIERRA, INC ]
