Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
(described below) adds jitter. See the “TDM Service in the ETT1 and TTX Switch Cores” App Note
for a more thorough discussion of TDM_Sync jitter and its consequences.
On receiving a Suggested_TDM_Sync signal, the Scheduler computes the period at which the
Suggested_TDM_Sync signals are arriving. The Scheduler then uses this period to determine the next
period at which it sends a TDM_Sync to all ETT1 ports. The period of the TDM_Sync signals will track the
period of the incoming Suggested_TDM_Sync signals. However the phase of the TDM_Sync signals may
be shifted relative to the Suggested_TDM_Sync signals. Internally the Scheduler has a digital PLL which
will gradually cause the transmitted TDM_Sync signal to have a fixed phase offset relative to the incoming
Suggested_TDM_Sync signal. Figure 31 shows the passage of signals.
Figure 31. Signal Flow
ETT1 core
Linecard
ETT1 Port
TDM_Sync
TDM Control Packet
Suggested_TDM_Sync
ETT1 Scheduler
TDM Control Packet
TDM Control Packet
Designated
Linecard
ETT1 Port
TDM_Sync
TDM_Sync
Linecard
ETT1 Port
TDM Control Packet
After a count of TDM_Period cell times, the designated line card will send another Suggested_TDM_Sync,
the line card TDM period counter will re-initialize and the process will repeat. If the Scheduler sees three
TDM periods go by without receiving another Suggested TDM sync, it will trigger an interrupt and continue
to send TDM_Syncs to the ports at the current period.
1.5.5 Configuring the TDM Service
Before TDM cells can flow the system must be configured. This involves the following:
1. Configure the TDM tables in all ports that will send or receive TDM cells.
2. Configure the Scheduler in the appropriate mode for TDM synchronization.
3. Enable TDM cells.
62
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
