RELEASED
PM73123 AAL1GATOR-8
DATASHEET
PMC-2000097
ISSUE 2
8 LINK CES/DBCES AAL1 SAR
difference in MF alignment on both sides of the ATM network. To align the MF
structure in the cell with the external MF pulse, ALIGN_MF should be set. If
MF_ALIGN_MODE is set to ALIGN_MF then RALP will not only queue up one
CDVT worth of time of data but will also delay the write pointer to the next MF
boundary. This method will insure MF alignment across the ATM network but will
add variable delay which could be between 0 and 3 ms(T1)/2 ms(E1).
If enabled, when a queue enters UNDERRUN or exits UNDERRUN an entry is
made into the RCVN_STAT_FIFO indicating the QUEUE number and setting
either the ENTER_UNDERRUN bit or the EXIT_UNDERRUN bit. These
conditions can be disabled from causing an entry in the RCVN_STAT_FIFO.
When an entry is made in the RCVN_STAT_FIFO, this event may cause the
INTB line to go low if the A1SP interrupt is enabled and the
RSTAT_FIFO_EMPB_EN is set and A1SP_INTR_EN is setB.
Refer to line items 5 and 6 in Figure 50 on page 129 that show how a start up
after an underrun occurs.
9.2.2.2.8 Pointer Processing
When an incoming cell has a cell pointer, the cell pointer is checked against the
local pointer value maintained by the RALP. A single pointer mismatch causes no
corrective actions. The pointer is ignored and the cell is used as if it contained
valid data. If two consecutive pointer mismatches occur, then the RALP forces an
underrun condition that causes the receiver to realign to the next incoming
pointer. The proper R_COND_DATA and frozen signaling are played out until the
new pointer is found and one CDVT worth of time has passed. The
PTR_MISMATCH sticky bit is set when the pointer mismatch occurs. The
FORCED_UNDERRUN sticky bit is set each time a cell is received and dropped
during the forced underrun condition. Then, the underrun and pointer search bits
are set, as described previously in section 9.2.2.2.7 “Underrun” on page 123.
Only one pointer is supposed to be received within a sequence of 8 cells (SN 0 –
SN 7). If more than one pointer is received or if no pointers are received in an
otherwise error free sequence of 8 cells, then the PTR_RULE_ERROR sticky bit
will be set. Pointers are also supposed to be less than or equal to 93 or equal to
the dummy value 127. If a pointer is received that does not fall within the legal
range and no other SN error occurred the PTR_RULE_ERROR sticky bit will be
set.
If the received cell is potentially bad as determined by SN processing, but should
contain a pointer, the pointer is not checked against the local pointer. However, in
this situation, and when cells are inserted, if the next received pointer
mismatches, then a PTR_MISMATCH error is reported and a forced underrun
PMC-SIERRA, INC. PROPRIETARY AND CONFIDENTIAL
125
PMC [ PMC-SIERRA, INC ]
