Transaction Routing; Transaction Reordering; Table 3.5 Switch Routing Methods - IDT 89HPES24N3A User Manual

IDT Theory of Operation
Notes
PES24N3A User Manual

Transaction Routing

The PES24N3A supports routing of all transaction types defined in the PCIe base 1.1 specification. This
includes routing of specification-defined transactions as well as those that may be used in vendor defined
messages and in future revisions of the PCIe specification.
Note: The PES24N3A supports routing of trusted configuration transactions.
Specifically, the PES24N3A supports the following type of routing:
– Address routing with 32-bit or 64-bit format
– ID based routing using bus, device and function numbers.
– Implicit routing utilizing
• Route to root
• Broadcast from root
• Local - terminate at receiver
• Gathered and routed to root
A summary of TLP types that use the above routing methods is provided in Table 3.5.
Routing Method
Route by Address
ID Based Routing
Imlicit Routing - Route to Root
Implicit Routing - Broadcast
from Root
Implicit Routing - Local
Implicit Routing - Gathered
and Routed to Root
1.
The only Gathered and Routed to Root message supported is a PME_TO_Ack message received on a
downstream port.

Transaction Reordering

Each IFB has a 25-bit free-running timer which is clocked at the 250 MHz core clock frequency. When a
TLP is enters the IFB, a 25-bit time-stamp of when the TLP arrived is stored in a descriptor associated with
the TLP. This time-stamp is used to implement a switch time-out and to provide a relative order of TLPs in
the IFB.
The IFB contains four input queues per port. These queues are the posted transaction queue (posted
queue), the non-posted transaction queue (non-posted queue), the completion transaction queue (comple-
tion queue) and an insertion buffer to hold TLPs generated by the stack.
While there are four physical queues in the IFB, TLPs in the insertion buffer are either posted or comple-
tion TLPs. Using the time-stamp with each TLP, the IFB logically merges the head of the completion queue
with the appropriate TLP type queue. Thus, the IFB has three logical queue heads corresponding to posted,
non-posted and completion TLPs.
The IFB examines information associated with the heads of the three logical queues, and presents a
signal called "valid" to the switch core for each TLP that may be dispatched. Along with the "valid" signal,
the IFB indicates the destination port, payload size, and relative age of the TLPs. This information is used
by the switch core scheduling and port arbitration logic to select a TLP to transfer through the switch core.
TLP Type Using Routing Method
MRd, MrdLk, MWr, IORd, IOWr, Msg, MsgD
CfgRd0, CfgWr0, CfgRd1, CfgWr1, TCfgRd, TCfgWr, Cpl,
CpdD, CplLk, CplDLk, Msg, MsgD
Msg, MsgD
Msg, MsgD
Msg, MsgD
Only supported for PME_TO_Ack messages in response to a
1
root initiated PME_Turn_Off message.

Table 3.5 Switch Routing Methods

3 - 4 April 10, 2008