PM9313 datasheet(65/343 Pages) PMC

65 / 343 page

PM9311/2/3/5 ETT1™ CHIP SET

PMC-2000164

ISSUE 3

ENHANCED TT1™ SWITCH FABRIC

Released

Data Sheet

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

PMC-Sierra, Inc.

1.5.4.1

TDM Sync Driven by the EPP

The EPP can be programmed to send a Suggested_TDM_Sync to the Scheduler once every N+1 celltimes

by writing N to the EPP’s TDM Sync Generation Control register and writing 1 to the Enable TDM Sync

Generation register. The TDM table select is also a field of the TDM Sync Generation Control register. The

Scheduler is programmed to listen to the Suggested_TDM_Sync from a designated port.

The advantage of this method over the third method is that the only exposure to jitter (uncertainties in

delay) on the TDM_Sync is after the EPP sends the TDM Control Packet to the linecard, due to crossing

asynchronous clock domains (and subport-ordering delay in subport mode). The advantage of this method

over the second method is that when using two Schedulers for fault tolerance, the second method requires

synchronous OOB writes to program the Schedulers at exactly the same time; this method provides a

synchronous Suggested_TDM_Sync to the two Schedulers instead.

A possible disadvantage of this method is that TDM Sync is synchronous to the ETT1’s core clock, not to

the linecard’s clock or any other external synchronization signal.

1.5.4.2

TDM Sync Driven by the Scheduler

The Scheduler can be programmed to generate its own TDM_Sync signals once every N+1 celltimes using

the Scheduler’s TDM Control register. The TDM table select is also controlled via the TDM Control register.

The Scheduler ignores Suggested_TDM_Sync from all ports.

The advantages of this method are simplicity and low jitter, similar to the first method.

The disadvantage of this method is that when using two Schedulers for fault tolerance, this method

requires synchronous OOB writes to program the Schedulers at exactly the same time; if the Schedulers’

TDM Control registers are enabled to send TDM Sync at different times, then all EPPs will report

mismatching frames from the two Schedulers. Scheduler refresh will not synchronize Scheduler-generated

TDM Syncs.

1.5.4.3

TDM Sync Driven by a Designated Linecard

Any linecard can send a Suggested_TDM_Sync to its ETT1 port, using a LCS TDM Control Packet, every

TDM_Period cells. The TDM Control Packet also specifies which of the two TDM tables should be used.

When the EPP receives a TDM Control Packet it sends a Suggested_TDM_Sync signal to the Scheduler.

The Scheduler is programmed to listen to the Suggested_TDM_Sync from a designated port.

The advantage of this method is that an external synchronization source can be used.

The disadvantage of this method is that there is much more exposure to jitter in TDM_Sync. Asynchronous

clock domain crossings (and subport-ordering delays in subport mode) will cause delay variations at

multiple stages: the LCS request for the Suggested_TDM_Sync Control Packet, the LCS grant, the

delivery of the Suggested_TDM_Sync Control Packet payload, and finally the delivery of the TDM_Sync

Control Packet from the ETT1 to the linecards. Additionally, the Scheduler’s internal digital TDM_Sync PLL

PM9313 Datasheet(PDF) 65 Page - PMC-Sierra, Inc

PM9313 Datasheet(HTML) 65 Page - PMC-Sierra, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL