IDT Theory of Operation
PES24N3A User Manual
3 - 8
April 10, 2008
Notes
pler queue transfer is initiated). However, since the upstream input frame buffer has a queue per transac-
tion type, it is possible for multiple upstream to downstream transactions to simultaneously request service.
In such a situation, the oldest transaction (i.e., the one with the oldest time-stamp) is selected.
Peer-to-Peer Transactions
The broadest definition of a peer-to-peer transaction is a transaction that originates at one endpoint and
targets another endpoint (i.e., the endpoints are peers). In the context of the PES24N3A, transactions
between downstream ports are referred to as peer-to-peer transactions. However, depending on system
topology and configuration, transactions between the upstream port and a downstream port may also be
peer-to-peer (i.e., between endpoints). While it is understood that such transactions may be peer-to-peer, in
the context of the PES24N3A these are not considered peer-to-peer transactions.
Thus, a peer-to-peer transaction in this specification refers to a transaction which originates at a
PES24N3A downstream port and targets another PES24N3A downstream port. While the architecture of
the PES24N3A supports peer-to-peer transactions, the performance of these transactions has not been
optimized since in fan-out applications peer-to-peer transactions are rare.
Some systems view peer-to-peer transactions as a potential security vulnerability since this capability
allows one endpoint to modify the state of another without protection checks. When the Disable Peer-to-
Peer (DP2P) bit is set in the Switch Control (SWCTL) register, all PES24N3A peer-to-peer transactions are
disabled. In this mode, any transaction received at a PES24N3A downstream port that targets another
downstream port is treated as an unsupported request (UR). Enabling this mode may cause TLPs with legal
PCI system architecture routing to be terminated with an error. Thus, it is the responsibility of the system
designer and system software to ensure proper system operation in this mode.
The PES24N3A also supports selective disabling of peer-to-peer transactions in a matrix fashion. Asso-
ciated with each port is TLP Routing Control (Px_TROUTECTL) register. Each bit in the Port Routing
Disable (PRDIS) field in this register corresponds to a PES24N3A port (e.g., bit one corresponds to port
one). When a bit in this field is set, forwarding of TLPs is disabled to the corresponding port from port in
which the TROUTECTL register is located. TLPs with a disabled route are treated as an unsupported
request (UR).
–
Route-to-self can never be disabled.
–
Routing to the upstream port from a downstream port cannot be disabled.
–
-Routing to a downstream port from the upstream port cannot be disabled.
Bus Locking
The PES24N3A supports locked transactions, allowing legacy software to run without modification on
PCIe. Only one locked transaction sequence may be in progress at a time.
–
A locked transaction sequence is requested by the root by issuing a Memory Read Request -
Locked (MRdLk) transaction. A lock is established when a lock request is successfully completed
with a Completion with Data - Locked (CplDLk). A lock is released with an Unlock message (Msg).
When the PES24N3A receives a MRdLk transaction on its upstream port destined for a downstream
port, it forwards the MRdLK transaction to the downstream port and locks the downstream port so that all
subsequent TLPs destined to that downstream port from ports other than the root are blocked until the lock
is released.
–
The MRdLK transaction obeys PCI ordering rules, meaning that all queued posted requests for
the downstream port are completed prior to the MRdLK being transmitted. The MRdLK is allowed
by bypass queued non-posted requests and completions.
–
When only the downstream port is locked, no transactions destined to any other port are blocked
(e.g., transactions from the other downstream ports to the upstream port and peer-to-peer trans-
actions are not blocked)
When a CplDLk is returned by the locked downstream port, the upstream port becomes locked causing
all transactions destined to the upstream port from sources other than the locked downstream port (i.e.,
other downstream ports) to be blocked. If the lock is unsuccessful, then a CPlLk is returned by the down-
Summary of Contents for 89HPES24N3A
Page 10: ...IDT Table of Contents PES24N3A User Manual iv April 10 2008 Notes...
Page 12: ...IDT List of Tables PES24N3A User Manual vi April 10 2008 Notes...
Page 14: ...IDT List of Figures PES24N3A User Manual viii April 10 2008 Notes...
Page 18: ...IDT Register List PES24N3A User Manual xii April 10 2008 Notes...
Page 64: ...IDT Link Operation PES24N3A User Manual 4 8 April 10 2008 Notes...
Page 88: ...IDT Power Management PES24N3A User Manual 7 4 April 10 2008 Notes...
Page 160: ...IDT Configuration Registers PES24N3A User Manual 9 66 April 10 2008 Notes...
