Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Configuring the tables is straightforward, as described in Section 1.5.2 “TDM Reservation Tables”. The
rules for the tables are:
(a) No port can source more than one TDM cell at any cell time.
(b) No port can receive more than one cell at any cell time.
(c) The linecard must send the cells to the EPP:
- in order, and
- before the current TDM slot reaches the slot reserved for that cell.
(d) Subport mode: The TDM Reservation Table can specify the same ingress subport only once every four
time slots.
(e) Subport mode: The TDM Reservation Table can not specify the same egress subport more than 48
time slots within a moving window of 192 time slots. This constraint is caused by the TDM output
queue.
Item (c) above is important to understand: the EPP will buffer all ingress TDM cells before they are sent
through the ETT1 fabric. The EPP can only buffer 96 TDM cells at the ingress. The linecard must be able
to send TDM cells to meet the average and the burst rate that are implied by the TDM table configuration.
So, if the linecard is operating at 20M cells/sec, for example, while the ETT1 fabric operates at 25M
cells/sec then the linecard must not reserve a contiguous burst of 128 TDM slots because it would be
unable to supply the last few cells in time for their reservations.
The next step is to configure the Scheduler. The Scheduler TDM service is controlled via its TDM Control
register. The first aspect to configure is the source of the Suggested_TDM_sync signal. If a linecard or
EPP will supply the Suggested_TDM_sync signal then configure the TDM Control register with the
selected port and set the Current Port valid bit. If a linecard or EPP does not supply the Suggested_TDM_
sync signal then the Scheduler must be configured with the desired TDM_Period: write the desired period
into the Initial Period field and toggle (0 to 1 to 0) the Load Initial Period control bit. In all cases the Enable
bit (bit 31) of the Scheduler’s TDM Control register should be set to 1.
The final stage of configuring the Scheduler is to write the desired value to the Enable TDM traffic register.
Each of the 32 bits should be set to 1 for those ports that will send or receive TDM traffic.
1.5.6 Changing the Source of the Suggested Sync
If the Scheduler is configured to use an external (port or linecard) source for the Suggested_TDM_sync,
then you can change the source port by writing a new value into the port field of the TDM Control register.
Once the new port starts to supply the Suggested_TDM_sync signal then the Scheduler will adjust the
frequency and phase of the transmitted TDM_Sync signal to match that of the new incoming signal. The
Scheduler will change the frequency of the outgoing sync signal once it has seen three Suggested_TDM_
sync signals, but it will only gradually adjust the phase. The phase of the outgoing TDM_Sync will be
adjusted by one cell time in every TDM_period.
NOTE: The phase reference for the Scheduler is the received Suggested_TDM_sync signal,
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
63
PMC [ PMC-SIERRA, INC ]
