RELEASED
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
5.2 PORT STATE
The Scheduler controls all cell flow within the fabric for both normal, best-effort cells and TDM cells. The
Scheduler can enable and disable cell flow on a port-by-port and class-of-service basis. When a new port
is added to the system, it can be tested offline without affecting existing traffic flows.
Each Scheduler port has a very simple state machine, as shown in Figure 66. The port’s current state
determines the type of cells it can, and cannot, forward through the fabric.
Figure 66. Port State Machine
reset or link is not Ready
Disabled
SNBPRT[port] = 1
AND link is Ready
SNBPRT[port] = 0
OR link is not Ready
Enabled
Refresh cell
Refreshing
Ordinary cell
Refresh cell
Refresh_done cell
Refresh_done cell
Refreshed
After reset, the port is in the disabled state. No cells will flow to or from this port when it is disabled.
Once the enable non-TDM traffic register for this port is set to 1, then the port is enabled. While the port is
enabled, it receives requests from the EPP and issues requests to the arbiter. It receives grants from the
arbiter and passes those grants to the EPP.
It also receives routing tags that it passes on to the EPP. At any time if errors are received on the
appropriate serial link then the port will be returned to the disabled state and must be reset before it can be
enabled.
The CPU initiates a Scheduler refresh by issuing a “Go Refresh” command to the EPP. The EPP then
sends 384 Refresh cells to the Scheduler. The Scheduler port transitions to the refreshing state as soon as
it receives the first of these Refresh cells. Once the EPP has sent all of the Refresh cells it then sends
Refresh_Done cells, causing the Scheduler port to transition to the refreshed state. The CPU then
terminates the refresh operation by issuing a “Go Scheduler” command to the EPP. This causes the EPP
to send ordinary cells. As soon as the Scheduler port receives an ordinary cell it will transition back to the
enabled state.
256
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
PMC [ PMC-SIERRA, INC ]
